Triangle Seminars
July 2021
Thu
29 Jul 2021
Integrability and chaos in SYM theories from anomalous-dimension spectra
Anne Spiering
(Trinity College Dublin)
Abstract:
The discovery of integrability in planar N=4 SYM theory led to considerable advances in the computation of its planar anomalous
dimension spectrum. Less is known at the non-planar level where the theory is assumed to be non-integrable. I will show how statistical properties of numerical anomalous dimension spectra can give insight into the symmetries of the underlying model and that the N=4 SYM non-planar spectrum and its beta-deformed version are well described by random matrix theory, indicating their quantum-chaotic nature. Doing so I will also discuss on-going work on using on-shell methods to obtain the dilatation operator for deformed versions of N=4 SYM theory. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
The discovery of integrability in planar N=4 SYM theory led to considerable advances in the computation of its planar anomalous
dimension spectrum. Less is known at the non-planar level where the theory is assumed to be non-integrable. I will show how statistical properties of numerical anomalous dimension spectra can give insight into the symmetries of the underlying model and that the N=4 SYM non-planar spectrum and its beta-deformed version are well described by random matrix theory, indicating their quantum-chaotic nature. Doing so I will also discuss on-going work on using on-shell methods to obtain the dilatation operator for deformed versions of N=4 SYM theory. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
22 Jul 2021
Tidal effects from quantum field theory
Kays Haddad
(Niels Bohr Institute)
Abstract:
Recently there has been great success in describing the inspiral phase of compact binary coalescence in General Relativity (GR) using scattering amplitudes. These efforts aim to improve the precision of gravitational wave (GW) templates used by detectors to identify GW events and test GR. The majority of this work has focused on describing a pair of objects that do not tidally deform. However real objects do tidally deform, and future GW detectors will be increasingly sensitive to such deformations. It has been shown that scattering amplitudes are applicable to the description of tidal effects as well. In this talk we discuss the application of the Hilbert series to the characterization of an entire class of tidal effects: those involving two powers of the Weyl tensor and objects with spin 0 and 1/2. The Hilbert series guides us in the construction of actions describing these effects, which we then use to calculate the leading-PM tidal scattering amplitude. With the amplitude in hand, we compute several classical quantities and compare to the literature where possible. [for zooom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Recently there has been great success in describing the inspiral phase of compact binary coalescence in General Relativity (GR) using scattering amplitudes. These efforts aim to improve the precision of gravitational wave (GW) templates used by detectors to identify GW events and test GR. The majority of this work has focused on describing a pair of objects that do not tidally deform. However real objects do tidally deform, and future GW detectors will be increasingly sensitive to such deformations. It has been shown that scattering amplitudes are applicable to the description of tidal effects as well. In this talk we discuss the application of the Hilbert series to the characterization of an entire class of tidal effects: those involving two powers of the Weyl tensor and objects with spin 0 and 1/2. The Hilbert series guides us in the construction of actions describing these effects, which we then use to calculate the leading-PM tidal scattering amplitude. With the amplitude in hand, we compute several classical quantities and compare to the literature where possible. [for zooom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
June 2021
Tue
29 Jun 2021
The classical interior of black holes in holography
Sean Hartnoll
(ITP Stanford University)
Abstract:
The exterior dynamics of black holes has played a major role in holographic duality, describing the approach to thermal equilibrium of strongly coupled media. The interior dynamics of black holes in a holographic setting has, in contrast, been largely unexplored. I will describe recent work investigating the classical interior dynamics of various holographic black holes. I will discuss the nature of the singularity, the absence of Cauchy horizons and a new kind of chaotic behavior that emerges in the presence of charged scalar fields.
[please email a.held@imperial.ac.uk for zoom link or password]
The exterior dynamics of black holes has played a major role in holographic duality, describing the approach to thermal equilibrium of strongly coupled media. The interior dynamics of black holes in a holographic setting has, in contrast, been largely unexplored. I will describe recent work investigating the classical interior dynamics of various holographic black holes. I will discuss the nature of the singularity, the absence of Cauchy horizons and a new kind of chaotic behavior that emerges in the presence of charged scalar fields.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Tue
22 Jun 2021
On Vacuum Transitions and the String Lanscape
Senarath de Alwis
(University of Colorado)
Abstract:
I discuss from a Hamiltonian (Lorentzian) perspective the calculations of vacuum transitions in flat space field theory and in gravitational backgrounds without the use of problematic Euclidean arguments. Some implications for the string theory landscape are highlighted.
[please note the unusual time]
[please email a.held@imperial.ac.uk for zoom link or password]
I discuss from a Hamiltonian (Lorentzian) perspective the calculations of vacuum transitions in flat space field theory and in gravitational backgrounds without the use of problematic Euclidean arguments. Some implications for the string theory landscape are highlighted.
[please note the unusual time]
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
17 Jun 2021
Integrability Gong Show
various speakers
Abstract:
This is the last appointment before September for the London Integrability Journal Club. We will have four 10+5 mins talks by:
- Ilija Buric (DESY), "Defect conformal blocks from the Iwasawa decomposition"
- Luigi Guerrini (U. of Parma), "A duality for the latitude Wilson loop in ABJM",
-Daniele Gregori (U. of Bologna), "Integrability and cycles of deformed N=2 gauge theory"
- Enrico Olivucci (Perimeter), "Hexagons in Fishnet theories: direct derivation".
Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
This is the last appointment before September for the London Integrability Journal Club. We will have four 10+5 mins talks by:
- Ilija Buric (DESY), "Defect conformal blocks from the Iwasawa decomposition"
- Luigi Guerrini (U. of Parma), "A duality for the latitude Wilson loop in ABJM",
-Daniele Gregori (U. of Bologna), "Integrability and cycles of deformed N=2 gauge theory"
- Enrico Olivucci (Perimeter), "Hexagons in Fishnet theories: direct derivation".
Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Tue
15 Jun 2021
Discovering Lepton Flavour Universality Violating New Physics
Andreas Crivellin
(CERN, Zurich University, PSI Villigen)
Abstract:
While the LHC has not discovered any new particles directly yet, hints for the violation of lepton flavour universality (satisfied within the SM) accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models.
[please email a.held@imperial.ac.uk for zoom link or password]
While the LHC has not discovered any new particles directly yet, hints for the violation of lepton flavour universality (satisfied within the SM) accumulated in recent years. In particular, deviations from the SM predictions were observed in semi-leptonic B decays (b->sll and b->ctau), in the anomalous magnetic moment of the muon (g-2), in leptonic tau decays and di-electron searches. Furthermore, also the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly, can be interpreted as a sign of lepton flavour universality violation. In this talk I review the status of these anomalies and give an overview of the possible interpretations in terms of new physics models.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
10 Jun 2021
Dually weighted graphs and 2d quantum gravity
Vladimir Kazakov
(ENS Paris)
Abstract:
Dually weighted graphs (DWG) are planar Feynman graphs bearing two sets of couplings: one set of usual couplings \(t_n\) attached to the vertices of valence \(n\), and another set of dual couplings \(t_n^*\) attached to the faces (dual vertices) of valence \(n\). Such couplings allow a deep control on possible shapes of planar graphs. For example, if one turns on only the couplings \(t_4\) and \(t_4^*\) the graph takes a ''fishnet form'' of a regular square lattice. The problem of counting of such graphs can be formulated as a modified hermitian one matrix model with an extra constant matrix. The partition function can be then represented in terms of the ''character expansion'' over Young tableaux, solvable by the saddle point approximation. I will review old results on DWG from my papers with M.Staudacher and Th.Wynter, including the techniques of computing Schur characters of a large Young tableau and deriving the elliptic algebraic curve for counting of planar quadrangulations. Then I will present new results from our ongoing work with F.Levkovich-Maslyuk where we count the disc quadrangulations with large, macroscopic area and boundary. This allows to extract interesting continuous limit of fluctuating 2d geometry, interpolating between the ''almost'' flat disc with a few dynamical conical defects and the disc partition function for pure 2d quantum gravity, generalizing old results for the spherical topology. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Dually weighted graphs (DWG) are planar Feynman graphs bearing two sets of couplings: one set of usual couplings \(t_n\) attached to the vertices of valence \(n\), and another set of dual couplings \(t_n^*\) attached to the faces (dual vertices) of valence \(n\). Such couplings allow a deep control on possible shapes of planar graphs. For example, if one turns on only the couplings \(t_4\) and \(t_4^*\) the graph takes a ''fishnet form'' of a regular square lattice. The problem of counting of such graphs can be formulated as a modified hermitian one matrix model with an extra constant matrix. The partition function can be then represented in terms of the ''character expansion'' over Young tableaux, solvable by the saddle point approximation. I will review old results on DWG from my papers with M.Staudacher and Th.Wynter, including the techniques of computing Schur characters of a large Young tableau and deriving the elliptic algebraic curve for counting of planar quadrangulations. Then I will present new results from our ongoing work with F.Levkovich-Maslyuk where we count the disc quadrangulations with large, macroscopic area and boundary. This allows to extract interesting continuous limit of fluctuating 2d geometry, interpolating between the ''almost'' flat disc with a few dynamical conical defects and the disc partition function for pure 2d quantum gravity, generalizing old results for the spherical topology. –– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Tue
8 Jun 2021
Towards the path integral for gravity
Neil Turok
(Perimeter Institute and University of Edinburgh)
Abstract:
We show how Feynman's path integral for quantum mechanics may be defined without a Wick rotation to imaginary time.
Instead, we employ analytic continuation (and Cauchy's theorem) in the complexified space of paths being integrated over. We outline an existence proof and describe applications to both nonrelativistic quantum mechanics and to interference patterns due to gravitational microlensing in radio astronomy.
[please email a.held@imperial.ac.uk for zoom link or password]
We show how Feynman's path integral for quantum mechanics may be defined without a Wick rotation to imaginary time.
Instead, we employ analytic continuation (and Cauchy's theorem) in the complexified space of paths being integrated over. We outline an existence proof and describe applications to both nonrelativistic quantum mechanics and to interference patterns due to gravitational microlensing in radio astronomy.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
3 Jun 2021
A gravity interpretation for the Bethe ansatz expansion of the N=4 SYM superconformal index
Ofer Aharony
(Weizmann Institute)
Abstract:
This (blackboard) talk is based on 2104.13932 and on work in progress with Francesco Benini, Ohad Mamroud and Paolo Milan. I will begin by briefly reviewing the superconformal index of the d=4 N=4 SU(N) supersymmetric Yang-Mills theory, how it is related (in the large N limit) to counting black hole microstates, and how it can be computed. I will then review a specific way to compute the index called the Bethe ansatz expansion, and describe the known solutions to the Bethe ansatz equations, and what they contribute to the index in the large N limit, including both perturbative and non-perturbative terms in 1/N. The index is related to the partition function of N=4 SYM on S^3xS^1, and in the large N limit this should be related by the AdS/CFT correspondence to a sum over Euclidean gravity solutions with appropriate asymptotic behavior. I will show that each known Bethe ansatz contribution arises from a specific supersymmetric (complex) black hole solution, which reproduces both its perturbative and its non-perturbative behavior (the latter comes from wrapped Euclidean D3-branes). A priori there are many more gravitational solutions than Bethe ansatz contributions, but we show that by considering the non-perturbative effects, the extra solutions are ruled out, leading to a precise match between the solutions on both sides.–– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
This (blackboard) talk is based on 2104.13932 and on work in progress with Francesco Benini, Ohad Mamroud and Paolo Milan. I will begin by briefly reviewing the superconformal index of the d=4 N=4 SU(N) supersymmetric Yang-Mills theory, how it is related (in the large N limit) to counting black hole microstates, and how it can be computed. I will then review a specific way to compute the index called the Bethe ansatz expansion, and describe the known solutions to the Bethe ansatz equations, and what they contribute to the index in the large N limit, including both perturbative and non-perturbative terms in 1/N. The index is related to the partition function of N=4 SYM on S^3xS^1, and in the large N limit this should be related by the AdS/CFT correspondence to a sum over Euclidean gravity solutions with appropriate asymptotic behavior. I will show that each known Bethe ansatz contribution arises from a specific supersymmetric (complex) black hole solution, which reproduces both its perturbative and its non-perturbative behavior (the latter comes from wrapped Euclidean D3-branes). A priori there are many more gravitational solutions than Bethe ansatz contributions, but we show that by considering the non-perturbative effects, the extra solutions are ruled out, leading to a precise match between the solutions on both sides.–– Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Tue
1 Jun 2021
QFT for Gravity at All Scales
Michele Levi
(NBI Copenhagen)
Abstract:
We will present the state of the art in PN gravity, and its significant advancement via the
EFT of spinning gravitating objects. First, we will introduce the concept of a tower of EFTs
for the binary inspiral problem. We will then go over the intricate formulation of the EFT
of spinning objects. Finally, we will present some advanced recent results accomplished
within this framework.
[please email a.held@imperial.ac.uk for zoom link or password]
We will present the state of the art in PN gravity, and its significant advancement via the
EFT of spinning gravitating objects. First, we will introduce the concept of a tower of EFTs
for the binary inspiral problem. We will then go over the intricate formulation of the EFT
of spinning objects. Finally, we will present some advanced recent results accomplished
within this framework.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
May 2021
Wed
26 May 2021
Muon g-2: experiment, standard model and lattice QCD
Laurent Lellouch
(CNRS and Aix-Marseille U.)
Abstract:
Twenty years ago in an experiment at Brookhaven National Laboratory, physicists measured the muon's anomalous magnetic moment, \(a_\mu=(g_\mu-2)/2\), with a remarkable precision of 0.54 parts per million. Since then, the standard model prediction for \(a_\mu\) has exhibited a discrepancy with experiment of over 3 standard deviations, raising the tantalizing possibility of physical particles or forces as yet undiscovered. On April 7 a new experiment at Fermilab presented its first results, brilliantly confirming Brookhaven's measurement and bringing the discrepancy with the standard model to a near discovery level of 4.2 sigma. To fully leverage this and future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the standard model prediction with independent methods, and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of \(a_\mu\), I will present a precise lattice QCD calculation, by the BMW collaboration, of the contribution to this quantity that most limits the precision of the standard model prediction. The result of this calculation significantly reduces the gap between the standard model and experiment, and suggests that new physics may not be needed to explain the current, experimental, world-average value of \(a_\mu\).
[please email a.held@imperial.ac.uk for zoom link or password]
Twenty years ago in an experiment at Brookhaven National Laboratory, physicists measured the muon's anomalous magnetic moment, \(a_\mu=(g_\mu-2)/2\), with a remarkable precision of 0.54 parts per million. Since then, the standard model prediction for \(a_\mu\) has exhibited a discrepancy with experiment of over 3 standard deviations, raising the tantalizing possibility of physical particles or forces as yet undiscovered. On April 7 a new experiment at Fermilab presented its first results, brilliantly confirming Brookhaven's measurement and bringing the discrepancy with the standard model to a near discovery level of 4.2 sigma. To fully leverage this and future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the standard model prediction with independent methods, and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of \(a_\mu\), I will present a precise lattice QCD calculation, by the BMW collaboration, of the contribution to this quantity that most limits the precision of the standard model prediction. The result of this calculation significantly reduces the gap between the standard model and experiment, and suggests that new physics may not be needed to explain the current, experimental, world-average value of \(a_\mu\).
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
20 May 2021
Integrated four-point correlators in N=4 super Yang-Mills.
Congkao Wen
(QMUL)
Abstract:
We will study the correlation function of four superconformal primaries in N=4 super Yang-Mills (SYM) with SU(N) gauge group. Recently, very powerful methods have been developed to compute this correlator at finite coupling based on a new concept of integrated correlators, which are defined by integrating the correlator over spacetime coordinates with suitable integration measures. The integrated correlators can be computed using supersymmetric localisation. We will mostly focus on one of the integrated correlators. An exact expression was found for this integrated correlator for arbitrary values of coupling and N. The integrated correlator can be expressed as a two-dimensional lattice sum, which manifests the SL(2, Z) modular invariance of N=4 SYM. Furthermore, the result obeys an elegant Laplace-difference equation that relates the correlator of SU(N) theory with those of SU(N-1) and SU(N+1) theories. In perturbation, the formula is checked to be consistent with known results from more standard methods. Finally, one can reconstruct the unintegrated correlator with finite coupling for first few orders in large-N expansion, the results are shown to agree with known type IIB superstring amplitudes due to AdS/CFT duality. This talk will be mainly based on arxiv.org/abs/2102.09537 (a short version can be found at arxiv.org/abs/2102.08305). –- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
We will study the correlation function of four superconformal primaries in N=4 super Yang-Mills (SYM) with SU(N) gauge group. Recently, very powerful methods have been developed to compute this correlator at finite coupling based on a new concept of integrated correlators, which are defined by integrating the correlator over spacetime coordinates with suitable integration measures. The integrated correlators can be computed using supersymmetric localisation. We will mostly focus on one of the integrated correlators. An exact expression was found for this integrated correlator for arbitrary values of coupling and N. The integrated correlator can be expressed as a two-dimensional lattice sum, which manifests the SL(2, Z) modular invariance of N=4 SYM. Furthermore, the result obeys an elegant Laplace-difference equation that relates the correlator of SU(N) theory with those of SU(N-1) and SU(N+1) theories. In perturbation, the formula is checked to be consistent with known results from more standard methods. Finally, one can reconstruct the unintegrated correlator with finite coupling for first few orders in large-N expansion, the results are shown to agree with known type IIB superstring amplitudes due to AdS/CFT duality. This talk will be mainly based on arxiv.org/abs/2102.09537 (a short version can be found at arxiv.org/abs/2102.08305). –- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Tue
18 May 2021
The hazardous landscape of Affinesia
Jose Beltran Jimenez
(Salamanca University)
Abstract:
The standard formulation of General Relativity is based on a geometrical framework where the spacetime manifold is endowed with a Lorentzian metric and its associated Levi-Civita connection. Since the affine structure is independent of the metric, it is possible to extend this geometrical set-up to allow for more general connections, thus giving rise to the metric-affine framework where the new actors are the torsion and the non-metricity. After discussing how these two objects can provide equivalent descriptions of GR, I will discuss how pathologies arise in modified theories of gravity along different directions in the metric-affine landscape.
[please email a.held@imperial.ac.uk for zoom link or password]
The standard formulation of General Relativity is based on a geometrical framework where the spacetime manifold is endowed with a Lorentzian metric and its associated Levi-Civita connection. Since the affine structure is independent of the metric, it is possible to extend this geometrical set-up to allow for more general connections, thus giving rise to the metric-affine framework where the new actors are the torsion and the non-metricity. After discussing how these two objects can provide equivalent descriptions of GR, I will discuss how pathologies arise in modified theories of gravity along different directions in the metric-affine landscape.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
13 May 2021
BPS states and RG flows
Michele Del Zotto
(Uppsala U.)
Abstract:
The study of possible constraints on RG flows is an important question in our understanding of quantum field theory. In this talk I will discuss a constraint which arises by considering the spectrum of BPS excitations (an H-theorem). Examples are found in the context of four-dimensional supersymmetric quantum field theories with enough supersymmetry that the BPS spectrum is explicitly computable. Among others, we will discuss applications in the context of Maruyoshi-Song flows. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
The study of possible constraints on RG flows is an important question in our understanding of quantum field theory. In this talk I will discuss a constraint which arises by considering the spectrum of BPS excitations (an H-theorem). Examples are found in the context of four-dimensional supersymmetric quantum field theories with enough supersymmetry that the BPS spectrum is explicitly computable. Among others, we will discuss applications in the context of Maruyoshi-Song flows. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
13 May 2021
OPE coefficients in ABJM theory with giants
Yunfeng Jiang
(CERN)
Abstract:
In this talk, I will discuss a family of three-point functions in ABJM theory, both at weak and strong coupling. This family of three-point functions involve two BPS sub-determinant operators called giant gravitons and one single trace operator, which can be BPS or non-BPS. In the first part of the talk, I will explain how to compute this type of three-point function at weak coupling using a large N effective field theory. The structure constant is given by the overlap of an integrable matrix product state and a Bethe state. In the second part, I will first clarify the prescription of computation at strong coupling. I will show that it is important to perform an average over the moduli space and also take into account the contributions from wave functions. The prescription is tested in N=4 SYM theory and then applied to ABJM theory.––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
In this talk, I will discuss a family of three-point functions in ABJM theory, both at weak and strong coupling. This family of three-point functions involve two BPS sub-determinant operators called giant gravitons and one single trace operator, which can be BPS or non-BPS. In the first part of the talk, I will explain how to compute this type of three-point function at weak coupling using a large N effective field theory. The structure constant is given by the overlap of an integrable matrix product state and a Bethe state. In the second part, I will first clarify the prescription of computation at strong coupling. I will show that it is important to perform an average over the moduli space and also take into account the contributions from wave functions. The prescription is tested in N=4 SYM theory and then applied to ABJM theory.––––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed on Tuesday.
Posted by: andrea
Wed
12 May 2021
Gluon Scattering in AdS from CFT
๐ London
Xinan Zhou
(Princeton U., CTP)
Abstract:
In this talk, I will discuss AdS super gluon scattering amplitudes in various spacetime dimensions. These amplitudes are dual to correlation functions in a variety of non-maximally supersymmetric CFTs, such as the 6d E-string theory, 5d Seiberg exceptional theories, etc. I will introduce a powerful method based on symmetries and consistency conditions, and show that it fixes all the infinitely many four-point amplitudes at tree level. I will also point out many interesting properties and structures of these amplitudes, which include the flat space limit, Parisi-Sourlas-like dimensional reduction, hidden conformal symmetry, and a color-kinematic duality in AdS. Along the way, I will also review some earlier progress and the relation with this work. I will conclude with a brief discussion of various open problems. [please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
In this talk, I will discuss AdS super gluon scattering amplitudes in various spacetime dimensions. These amplitudes are dual to correlation functions in a variety of non-maximally supersymmetric CFTs, such as the 6d E-string theory, 5d Seiberg exceptional theories, etc. I will introduce a powerful method based on symmetries and consistency conditions, and show that it fixes all the infinitely many four-point amplitudes at tree level. I will also point out many interesting properties and structures of these amplitudes, which include the flat space limit, Parisi-Sourlas-like dimensional reduction, hidden conformal symmetry, and a color-kinematic duality in AdS. Along the way, I will also review some earlier progress and the relation with this work. I will conclude with a brief discussion of various open problems. [please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Tue
11 May 2021
Gravity: The force from the UV
Simon Caron-Huot
(McGill University)
Abstract:
Does our world respect causality at all energy scales? We explore constraints on low-energy dynamics which step from this assumption. Obstructions to a causal UV completion can be diagnosed using dispersive sum rules, which connect the infrared and ultraviolet. While dispersion relations originate in optics and quantum field theory, I will argue that their true purpose is gravity, where they become particularly powerful due to the maximal growth rate of this force with energy. This leads to the so-called graviton pole in sum rules. I will briefly review how, for non-gravitational low-energy effective theories, causality turns dimensional analysis estimates into sharp numerical bounds, and I will present initial results on gravitational effective theories.
[please email a.held@imperial.ac.uk for zoom link or password]
Does our world respect causality at all energy scales? We explore constraints on low-energy dynamics which step from this assumption. Obstructions to a causal UV completion can be diagnosed using dispersive sum rules, which connect the infrared and ultraviolet. While dispersion relations originate in optics and quantum field theory, I will argue that their true purpose is gravity, where they become particularly powerful due to the maximal growth rate of this force with energy. This leads to the so-called graviton pole in sum rules. I will briefly review how, for non-gravitational low-energy effective theories, causality turns dimensional analysis estimates into sharp numerical bounds, and I will present initial results on gravitational effective theories.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
6 May 2021
Towards a general map from Navier-Stokes to Maxwell via Einstein
Cynthia Keeler
(ASU)
Abstract:
[for zoom link please email s.nagyATqmul.ac.uk]
After a brief review of the cutoff-surface formulation of fluid-gravity duality, we explore the ``square root'' of the fluid-dual metrics via the classical-double copy, highlighting the constant vorticity flows and potential flows which have algebraically special Weyl double copy fields. We then present progress towards building the same map, from fluid solutions to gravitational solutions to Maxwell solutions, for generic fluids in 2+1 dimensions. This talk is based on JHEP 08 (2020) 147 published with ASU students Nikhil Monga and Tucker Manton, and forthcoming work.
[for zoom link please email s.nagyATqmul.ac.uk]
After a brief review of the cutoff-surface formulation of fluid-gravity duality, we explore the ``square root'' of the fluid-dual metrics via the classical-double copy, highlighting the constant vorticity flows and potential flows which have algebraically special Weyl double copy fields. We then present progress towards building the same map, from fluid solutions to gravitational solutions to Maxwell solutions, for generic fluids in 2+1 dimensions. This talk is based on JHEP 08 (2020) 147 published with ASU students Nikhil Monga and Tucker Manton, and forthcoming work.
Posted by: QMW
Thu
6 May 2021
Current operators in integrable models (a review)
Balazs Pozsgay
(Eotvos University Budapest)
Abstract:
Current operators describe the flow of the conserved charges in integrable models. Whereas lots of information was known about the charges, surprisingly the current operators remained unexplored for a very long time. I review recent results in this topic, which include an exact finite volume formula for the mean values of the current operators, their embedding into the Quantum Inverse Scattering Approach (Algebraic Bethe Ansatz), and connections with long range deformations and TTbar deformations. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed on Tuesday.
Current operators describe the flow of the conserved charges in integrable models. Whereas lots of information was known about the charges, surprisingly the current operators remained unexplored for a very long time. I review recent results in this topic, which include an exact finite volume formula for the mean values of the current operators, their embedding into the Quantum Inverse Scattering Approach (Algebraic Bethe Ansatz), and connections with long range deformations and TTbar deformations. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed on Tuesday.
Posted by: andrea
Wed
5 May 2021
Conformal Bootstrap and Critical Phenomena
๐ London
Andreas Stergiou
(Los Alamos)
Abstract:
Renormalization group methods have been used for almost 50 years to obtain results for critical exponents of conformal field theories (CFTs), while relying on assumptions and approximations that are not rigorously justified. The agreement with experiments is good in many cases, e.g. the 3D Ising model, but disagreements between theory and experiment that have remained unresolved for decades also exist. This indicates that our understanding of critical phenomena may be incomplete. More recently, the numerical conformal bootstrap, a fully nonperturbative method, has proven to be very powerful in calculating critical exponents and other physical observables of CFTs. In this talk we will review the numerical conformal bootstrap method and discuss potential resolutions it has suggested for unsettled questions pertaining to critical phenomena in frustrated magnets and structural phase transitions.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Renormalization group methods have been used for almost 50 years to obtain results for critical exponents of conformal field theories (CFTs), while relying on assumptions and approximations that are not rigorously justified. The agreement with experiments is good in many cases, e.g. the 3D Ising model, but disagreements between theory and experiment that have remained unresolved for decades also exist. This indicates that our understanding of critical phenomena may be incomplete. More recently, the numerical conformal bootstrap, a fully nonperturbative method, has proven to be very powerful in calculating critical exponents and other physical observables of CFTs. In this talk we will review the numerical conformal bootstrap method and discuss potential resolutions it has suggested for unsettled questions pertaining to critical phenomena in frustrated magnets and structural phase transitions.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Tue
4 May 2021
Cosmology as a tool to test fundamental physics
Lavinia Heisenberg
(ETH Zurich)
Abstract:
I will start by introducing the two fundamental pillars of Cosmology: General Relativity and the Cosmological Principle. General Relativity will be constructed both in the geometrical as well as in the particle physics perspective. After introducing some of the prominent effective field theories of gravity I will show how the Cosmological Principle can be realized in the different theories. I will then discuss how different theoretical consistency checks can be applied on them for their scrutiny, like conditions coming from a UV completion and quantum corrections. I will argue that we will need to combine this theoretical scrutiny program with different cosmological observations in order to disentangle between different dark energy models and test fundamental properties of gravity.
[please email a.held@imperial.ac.uk for zoom link or password]
I will start by introducing the two fundamental pillars of Cosmology: General Relativity and the Cosmological Principle. General Relativity will be constructed both in the geometrical as well as in the particle physics perspective. After introducing some of the prominent effective field theories of gravity I will show how the Cosmological Principle can be realized in the different theories. I will then discuss how different theoretical consistency checks can be applied on them for their scrutiny, like conditions coming from a UV completion and quantum corrections. I will argue that we will need to combine this theoretical scrutiny program with different cosmological observations in order to disentangle between different dark energy models and test fundamental properties of gravity.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
April 2021
Thu
29 Apr 2021
The Topology of Data: from String Theory to Cosmology to Phases of Matter
Gary Shiu
(Wisconsin U., Madison)
Abstract:
Abstract: We are faced with an explosion of data in many areas of physics, but very so often, it is not the size but the complexity of the data that makes extracting physics from big datasets challenging. As I will discuss in this talk, data has shape and the shape of data encodes the underlying physics. Persistent homology is a tool in computational topology developed for quantifying the shape of data. I will discuss three applications of topological data analysis: 1) identifying structure of the string landscape, 2) constraining cosmological parameters from CMB measurements and large scale structures data, and 3) detecting and classifying phases of matter. Persistent homology condenses these datasets into their most relevant (and interpretable) features, so that simple statistical pipelines are sufficient in these contexts. This suggests that TDA can be used in conjunction with machine learning algorithms and improves their architecture. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Abstract: We are faced with an explosion of data in many areas of physics, but very so often, it is not the size but the complexity of the data that makes extracting physics from big datasets challenging. As I will discuss in this talk, data has shape and the shape of data encodes the underlying physics. Persistent homology is a tool in computational topology developed for quantifying the shape of data. I will discuss three applications of topological data analysis: 1) identifying structure of the string landscape, 2) constraining cosmological parameters from CMB measurements and large scale structures data, and 3) detecting and classifying phases of matter. Persistent homology condenses these datasets into their most relevant (and interpretable) features, so that simple statistical pipelines are sufficient in these contexts. This suggests that TDA can be used in conjunction with machine learning algorithms and improves their architecture. [for zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
29 Apr 2021
Scattering Amplitudes Near the Origins: Localization and Globalization
Benjamin Basso
(ENS Paris)
Abstract:
I will talk about the behaviour of gluon scattering amplitudes in planar N=4 SYM near kinematical corners coined Origins where maximally-helicity-violating amplitudes are expected to be exactly Gaussian in the logs of the cross ratios and exactly predictable. In part 1, I will recall how much is known about this behaviour for the 6-gluon amplitude and interpret the result as a sort of quantum area convoluting the minimal surface TBA data with an effective coupling constant, known as the tilted cusp anomalous dimension. In part 2, I will present a generalization to any number of gluons and explore (some bit of) the emerging parterre of Origins. If time permits, I will discuss applications to scattering amplitudes in the null limit where all two-particle Mandelstam vanish simultaneously. The talk is based on a work in progress with Lance Dixon, Yu-Ting Liu and Georgios Papathanasiou. –– Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.
I will talk about the behaviour of gluon scattering amplitudes in planar N=4 SYM near kinematical corners coined Origins where maximally-helicity-violating amplitudes are expected to be exactly Gaussian in the logs of the cross ratios and exactly predictable. In part 1, I will recall how much is known about this behaviour for the 6-gluon amplitude and interpret the result as a sort of quantum area convoluting the minimal surface TBA data with an effective coupling constant, known as the tilted cusp anomalous dimension. In part 2, I will present a generalization to any number of gluons and explore (some bit of) the emerging parterre of Origins. If time permits, I will discuss applications to scattering amplitudes in the null limit where all two-particle Mandelstam vanish simultaneously. The talk is based on a work in progress with Lance Dixon, Yu-Ting Liu and Georgios Papathanasiou. –– Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
28 Apr 2021
Higher-derivative Supergravity and AdS4 Holography
๐ London
Valentin Reys
(Leuven U.)
Abstract:
This talk will discuss higher-derivative corrections to four-dimensional gauged supergravity and their holographic implications. After briefly reviewing the construction of N=2 supersymmetric higher-derivative invariants, I will introduce a four-derivative action parameterized by two real constants. In this theory, one can show that the two-derivative solutions are not modified by the higher-derivative corrections. This fact has important consequences for the regularized on-shell action, as well as for the thermodynamics of black hole solutions. Moreover, in the context of AdS4/CFT3 holography, I will explain how our results lead to an explicit expression for subleading corrections in the large-N expansion of supersymmetric partition functions of a large class of dual field theories arising from M2 and M5 branes.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
This talk will discuss higher-derivative corrections to four-dimensional gauged supergravity and their holographic implications. After briefly reviewing the construction of N=2 supersymmetric higher-derivative invariants, I will introduce a four-derivative action parameterized by two real constants. In this theory, one can show that the two-derivative solutions are not modified by the higher-derivative corrections. This fact has important consequences for the regularized on-shell action, as well as for the thermodynamics of black hole solutions. Moreover, in the context of AdS4/CFT3 holography, I will explain how our results lead to an explicit expression for subleading corrections in the large-N expansion of supersymmetric partition functions of a large class of dual field theories arising from M2 and M5 branes.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Wed
28 Apr 2021
Kaluza-Klein spectrometer from exceptional field theory
Henning Samtleben
(ENS Lyon)
Abstract:
I review new tools for the computation of Kaluza-Klein mass spectra associated with compactifications around various background geometries relevant for string theory. This includes geometries with little to no remaining symmetries, hardly accessible to standard methods. The new tools build on exceptional field theory, the duality covariant formulation of supergravity. Among the applications I discuss the stability of several non-supersymmetric AdS4 and AdS3 vacua, as well as Kaluza-Klein spectra around type IIB S-fold backgrounds.
Zoom:
https://zoom.us/j/98264204601?pwd=Z0xYdG1vVlEwU1M1bDhVcXQvWURPQT09
Meeting ID: 982 6420 4601
Passcode: 196883
I review new tools for the computation of Kaluza-Klein mass spectra associated with compactifications around various background geometries relevant for string theory. This includes geometries with little to no remaining symmetries, hardly accessible to standard methods. The new tools build on exceptional field theory, the duality covariant formulation of supergravity. Among the applications I discuss the stability of several non-supersymmetric AdS4 and AdS3 vacua, as well as Kaluza-Klein spectra around type IIB S-fold backgrounds.
Zoom:
https://zoom.us/j/98264204601?pwd=Z0xYdG1vVlEwU1M1bDhVcXQvWURPQT09
Meeting ID: 982 6420 4601
Passcode: 196883
Posted by: IC
Tue
27 Apr 2021
Topics in inflationary cosmology: reheating, gauge fields and gravitational waves
Kaloian Lozanov
(University of Illinois)
Abstract:
We will review our current understanding of reheating after inflation, including various aspects of the linear and nonlinear dynamics of the inflaton field, such as parametric resonance, the generation of metric perturbations and the effects of the nonlinear evolution on the post-inflationary expansion history. We will also review the recent progress in the understanding of the non-perturbative dynamics of dark vector fields during reheating and whether they can play the role of dark matter in the late universe. Finally, we will discuss phenomenologically interesting models of gauge fields during inflation which can give rise to detectable gravitational wave signatures.
[please email a.held@imperial.ac.uk for zoom link or password]
We will review our current understanding of reheating after inflation, including various aspects of the linear and nonlinear dynamics of the inflaton field, such as parametric resonance, the generation of metric perturbations and the effects of the nonlinear evolution on the post-inflationary expansion history. We will also review the recent progress in the understanding of the non-perturbative dynamics of dark vector fields during reheating and whether they can play the role of dark matter in the late universe. Finally, we will discuss phenomenologically interesting models of gauge fields during inflation which can give rise to detectable gravitational wave signatures.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
22 Apr 2021
Boundary-bulk relations in conformal/topological field theories
Liang Kong
(Shenzhen Institute of Quantum Science and Engineering, SUSTech)
Abstract:
[There will be a pre-seminar for students starting at 13:30. For zoom link please email s.nagyATqmul.ac.uk]
The relation between the physics of the bulk and that of a boundary plays an important role in quantum field theories, quantum gravity and condensed matter physics. In this talk, I will review a manifestation of this relation that can be summarized as a short statement: "the bulk is the center of a boundary". I will explain the meaning of "center" and provide a formal proof of this statement (arXiv:1702.00673). By including higher codimensional domain walls between boundaries, the boundary-bulk relation can be formulated mathematically as a higher functor. In lower dimensional cases, it becomes precise mathematical theorems. In the end, I will discuss the significances of this relation in the study of topological orders and topological phase transitions.
[There will be a pre-seminar for students starting at 13:30. For zoom link please email s.nagyATqmul.ac.uk]
The relation between the physics of the bulk and that of a boundary plays an important role in quantum field theories, quantum gravity and condensed matter physics. In this talk, I will review a manifestation of this relation that can be summarized as a short statement: "the bulk is the center of a boundary". I will explain the meaning of "center" and provide a formal proof of this statement (arXiv:1702.00673). By including higher codimensional domain walls between boundaries, the boundary-bulk relation can be formulated mathematically as a higher functor. In lower dimensional cases, it becomes precise mathematical theorems. In the end, I will discuss the significances of this relation in the study of topological orders and topological phase transitions.
Posted by: QMW
Thu
22 Apr 2021
Lattice nonlinear Schroedinger equation: history and open problems.
Vladimir Korepin
(YITP Stony Brook)
Abstract:
The model has many names:
Lieb-Liniger, Bose gas with delta interaction and nonlinear Schroedinger. A limiting case is called Tonks-Girardeau. It is solvable by algebraic Bethe ansatz.
We shall use notations of quantum inverse scattering method.
Applications will be mentioned. ––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed.
The model has many names:
Lieb-Liniger, Bose gas with delta interaction and nonlinear Schroedinger. A limiting case is called Tonks-Girardeau. It is solvable by algebraic Bethe ansatz.
We shall use notations of quantum inverse scattering method.
Applications will be mentioned. ––- Part of the London Integrability Journal Club. Please register at integrability-london.weebly.com if you are a new participant. The link will be emailed.
Posted by: andrea
Wed
21 Apr 2021
Current operators in integrable models: Review of recent results
๐ London
Balazs Pozsgay
(Eotvos Lorand U., Budapest, Inst. Theor. Phys.)
Abstract:
We review the recent progress regarding current operators in integrable models, focusing especially on integrable spin chains. These operators describe the flow of the conserved charges, and they are important for the construction of Generalized Hydrodynamics. They are also connected to long range deformations and TTbar-like deformations of the spin chains, and also to the theory of factorized correlation functions. We argue that these operators are very special, because their mean values can be computed relatively easily even in nested spin chains. This is rather unique because mean values in nested models are rather difficult to compute for generic operators. We review these various connections and also show how to construct current operators using the Quantum Inverse Scattering Approach, the canonical framework developed by the Leningrad school.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
We review the recent progress regarding current operators in integrable models, focusing especially on integrable spin chains. These operators describe the flow of the conserved charges, and they are important for the construction of Generalized Hydrodynamics. They are also connected to long range deformations and TTbar-like deformations of the spin chains, and also to the theory of factorized correlation functions. We argue that these operators are very special, because their mean values can be computed relatively easily even in nested spin chains. This is rather unique because mean values in nested models are rather difficult to compute for generic operators. We review these various connections and also show how to construct current operators using the Quantum Inverse Scattering Approach, the canonical framework developed by the Leningrad school.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Tue
20 Apr 2021
(please note that the time of this semiar has been moved to 15:30)
Cliff Burgess
(McMaster University and Perimeter Institute for Theoretical Physics)
Abstract:
(please note that the time of this semiar has been moved to 15:30)
(please note that the time of this semiar has been moved to 15:30)
Posted by: IC
Tue
20 Apr 2021
EFTs, Gravity and Clues from the UV
Clifford Burgess
(Perimeter Institute for Theoretical Physics and McMaster University)
Abstract:
Everyone seems to have strong opinions these days about what UV completions to gravity can tell us about lower-energy physics. Perceived difficulties finding inflationary solutions to string theory in particular have prompted re-examination of the utility of EFT methods, such as through the swampland trans-Planckian conjectures. This talk provides a curmudgeonly assessment of some of these proposals together with my own opinion about the likely low-energy take-aways of attempts to embed cosmology into string theory. If there is time I will describe some aspects of gravitation EFTs that really do seem to deviate from the standard Wilsonian picture.
[please note the unusual time]
[please email a.held@imperial.ac.uk for zoom link or password]
Everyone seems to have strong opinions these days about what UV completions to gravity can tell us about lower-energy physics. Perceived difficulties finding inflationary solutions to string theory in particular have prompted re-examination of the utility of EFT methods, such as through the swampland trans-Planckian conjectures. This talk provides a curmudgeonly assessment of some of these proposals together with my own opinion about the likely low-energy take-aways of attempts to embed cosmology into string theory. If there is time I will describe some aspects of gravitation EFTs that really do seem to deviate from the standard Wilsonian picture.
[please note the unusual time]
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
15 Apr 2021
A CFT Distance Conjecture
Eric Perlmutter
(IPhT)
Abstract:
[for zoom link, please email s.nagyATqmul.ac.uk]
We formulate conjectures relating the geometry of conformal manifolds to the spectrum of local operators in conformal field theories in d>2 spacetime dimensions. We focus on conformal manifolds with limiting points at infinite distance with respect to the Zamolodchikov metric. Our central conjecture is that all theories at infinite distance possess an emergent higher-spin symmetry, generated by an infinite tower of currents whose anomalous dimensions vanish exponentially in the distance. Our conjectures are related to the Distance Conjecture in the swampland program. We discuss the supporting evidence, their holographic interpretation, and implications for superconformal field theories.
[for zoom link, please email s.nagyATqmul.ac.uk]
We formulate conjectures relating the geometry of conformal manifolds to the spectrum of local operators in conformal field theories in d>2 spacetime dimensions. We focus on conformal manifolds with limiting points at infinite distance with respect to the Zamolodchikov metric. Our central conjecture is that all theories at infinite distance possess an emergent higher-spin symmetry, generated by an infinite tower of currents whose anomalous dimensions vanish exponentially in the distance. Our conjectures are related to the Distance Conjecture in the swampland program. We discuss the supporting evidence, their holographic interpretation, and implications for superconformal field theories.
Posted by: QMW
Wed
14 Apr 2021
Holographic Approaches to AdS Black Hole Entropy
Marina David
( University of Michigan)
Abstract:
Significant progress has been made regarding the microstate counting of extremal AdS black holes in the context of AdS/CFT, where the Cardy-like limit on the field side theory has often been used. I will discuss the implications of this limit on the gravity side and how it translates to a parameter space limit on the black hole solution. This limit, referred to as the gravitational Cardy limit, is applied to the Bardeen Horowitz near-horizon geometry to reproduce the Bekenstein-Hawking entropy via the Kerr/CFT correspondence, yielding a third approach to the computation of the entropy. Relaxing the gravitational Cardy limit, the computation can be further extended to near-extremality, where the heat capacity is found. For each case, extremal and near-extremal, the entropy from these different approaches match, providing a unique and universal expression for the entropy.
https://zoom.us/j/98264204601?pwd=Z0xYdG1vVlEwU1M1bDhVcXQvWURPQT09
Significant progress has been made regarding the microstate counting of extremal AdS black holes in the context of AdS/CFT, where the Cardy-like limit on the field side theory has often been used. I will discuss the implications of this limit on the gravity side and how it translates to a parameter space limit on the black hole solution. This limit, referred to as the gravitational Cardy limit, is applied to the Bardeen Horowitz near-horizon geometry to reproduce the Bekenstein-Hawking entropy via the Kerr/CFT correspondence, yielding a third approach to the computation of the entropy. Relaxing the gravitational Cardy limit, the computation can be further extended to near-extremality, where the heat capacity is found. For each case, extremal and near-extremal, the entropy from these different approaches match, providing a unique and universal expression for the entropy.
https://zoom.us/j/98264204601?pwd=Z0xYdG1vVlEwU1M1bDhVcXQvWURPQT09
Posted by: IC
Tue
13 Apr 2021
Bootstrapping surface defects in four-dimensional superconformal theories
Madalena Lemos
(Durham University)
Abstract:
We will motivate and introduce the study of conformal defects in superconformal field theories (SCFTs). We will show how symmetries constrain the anomaly coefficients of BPS defects. In the case of N=(2,2) surface defects in four-dimensional N=2 SCFTs these anomaly coefficients can be computed by studying a protected sub-sector captured by a two-dimensional chiral algebra.
[please email a.held@imperial.ac.uk for zoom link or password]
We will motivate and introduce the study of conformal defects in superconformal field theories (SCFTs). We will show how symmetries constrain the anomaly coefficients of BPS defects. In the case of N=(2,2) surface defects in four-dimensional N=2 SCFTs these anomaly coefficients can be computed by studying a protected sub-sector captured by a two-dimensional chiral algebra.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
8 Apr 2021
Moduli space of vortices and 3d supersymmetric gauge theories
Heeyeon Kim
(Rutgers)
Abstract:
[For zoom link please email s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13:30]
I will discuss the geometric interpretation of the twisted index of 3d supersymmetric gauge theories on a closed Riemann surface. I will show that the twisted index reproduces the virtual Euler characteristic of the moduli space of solutions to vortex equations on the Riemann surface. I will also discuss 3d N = 4 mirror symmetry in this context, which implies non-trivial relations between enumerative invariants associated to the moduli space of vortices. Finally, I will comment on level structures and a wall-crossing formula of the twisted indices derived from the gauge theory point of view.
[For zoom link please email s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13:30]
I will discuss the geometric interpretation of the twisted index of 3d supersymmetric gauge theories on a closed Riemann surface. I will show that the twisted index reproduces the virtual Euler characteristic of the moduli space of solutions to vortex equations on the Riemann surface. I will also discuss 3d N = 4 mirror symmetry in this context, which implies non-trivial relations between enumerative invariants associated to the moduli space of vortices. Finally, I will comment on level structures and a wall-crossing formula of the twisted indices derived from the gauge theory point of view.
Posted by: QMW
Thu
1 Apr 2021
Scrambling in Yang-Mills
Robert de Mello Koch
(Witwatersrand U.)
Abstract:
We study operators with a bare dimension that grows as N^2 in the large N limit. These operators are labeled by a Young diagram with p long rows, as well as a graph, with p nodes. The dilatation operator describing the mixing of these operators defines a Hamiltonian for excitations hopping on this graph. The scrambling and equilibration of the resulting dynamics is studied. [For zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
We study operators with a bare dimension that grows as N^2 in the large N limit. These operators are labeled by a Young diagram with p long rows, as well as a graph, with p nodes. The dilatation operator describing the mixing of these operators defines a Hamiltonian for excitations hopping on this graph. The scrambling and equilibration of the resulting dynamics is studied. [For zoom link please contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
1 Apr 2021
Affine Gaudin models and integrable sigma-models
Sylvain Lacroix
(University of Hamburg)
Abstract:
In this talk, I will discuss how the formalism of affine Gaudin models can be used to construct new integrable sigma-models. I will start by reviewing the construction of affine Gaudin models and their interpretation as integrable two-dimensional field theories. I will then explain how well-chosen realisations of these models give integrable coupled sigma model on an arbitrary number of copies of a Lie group G^N as well as integrable coset models on the quotient of G^N by a diagonal subgroup. In particular, I will discuss application of the latter construction to T^11 manifolds. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
In this talk, I will discuss how the formalism of affine Gaudin models can be used to construct new integrable sigma-models. I will start by reviewing the construction of affine Gaudin models and their interpretation as integrable two-dimensional field theories. I will then explain how well-chosen realisations of these models give integrable coupled sigma model on an arbitrary number of copies of a Lie group G^N as well as integrable coset models on the quotient of G^N by a diagonal subgroup. In particular, I will discuss application of the latter construction to T^11 manifolds. –- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
March 2021
Wed
31 Mar 2021
Supergravity excitations of stringy geometries
Oleg Lunin
(SUNY-Albany)
Abstract:
Motivated by the desire to understand the dynamics of light modes on
various gravitational backgrounds,
this talk summarizes recent results concerning properties of scalar,
vector, and tensor excitations of black holes and integrable stringy
geometries.
For rotating black holes and for certain Wess-Zumino-Witten models,
full separability of all dynamical equations is demonstrated, and
symmetries underlying this property are uncovered. For other classes
of integrable backgrounds, the energy spectra of various fields are
evaluated, and the algebraic constructions of the corresponding
eigenfunctions are presented.
Join Zoom Meeting
https://zoom.us/j/94137164225?pwd=ZTV3Z2c3aStOdk5sSFRRbkhQRUh5dz09
Meeting ID: 941 3716 4225
Passcode: 500873
Motivated by the desire to understand the dynamics of light modes on
various gravitational backgrounds,
this talk summarizes recent results concerning properties of scalar,
vector, and tensor excitations of black holes and integrable stringy
geometries.
For rotating black holes and for certain Wess-Zumino-Witten models,
full separability of all dynamical equations is demonstrated, and
symmetries underlying this property are uncovered. For other classes
of integrable backgrounds, the energy spectra of various fields are
evaluated, and the algebraic constructions of the corresponding
eigenfunctions are presented.
Join Zoom Meeting
https://zoom.us/j/94137164225?pwd=ZTV3Z2c3aStOdk5sSFRRbkhQRUh5dz09
Meeting ID: 941 3716 4225
Passcode: 500873
Posted by: IC
Wed
31 Mar 2021
On QFT in de Sitter
๐ London
Victor Gorbenko
(Stanford University)
Abstract:
I will discuss the tools we are developing to calculate correlation functions of primordial inflationary perturbations. In this talk, we will focus on the limit where gravitational excitations are neglected and the cosmological spacetime is assumed to be exactly de Sitter. Even in this simplifying limit, which corresponds to a Quantum Field Theory on a de Sitter background, very few examples of explicit analytic calculations exist and little is known about basic properties of the correlators. I will show that for any dS QFT there exists a theory formulated in a Euclidean Anti-de SItter space and which reproduces all the correlation functions. This leads to major technical simplifications and allows to demonstrate various analytic properties of the cosmological observables. Understanding of these properties has both phenomenological applications in inflation, as well as provides some hints about more fundamental description for cosmological spacetimes.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
I will discuss the tools we are developing to calculate correlation functions of primordial inflationary perturbations. In this talk, we will focus on the limit where gravitational excitations are neglected and the cosmological spacetime is assumed to be exactly de Sitter. Even in this simplifying limit, which corresponds to a Quantum Field Theory on a de Sitter background, very few examples of explicit analytic calculations exist and little is known about basic properties of the correlators. I will show that for any dS QFT there exists a theory formulated in a Euclidean Anti-de SItter space and which reproduces all the correlation functions. This leads to major technical simplifications and allows to demonstrate various analytic properties of the cosmological observables. Understanding of these properties has both phenomenological applications in inflation, as well as provides some hints about more fundamental description for cosmological spacetimes.
[please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Tue
30 Mar 2021
Cosmic String Interpretation of NANOGrav Pulsar Timing Data and its impact on Cosmic Archaeology with Gravitational Waves
Marek Lewicki
(University of Warsaw)
Abstract:
The NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gรยผรขหห(4รโ10^{รขหโ11},10^{รขหโ10}) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers. The SGWB produced by cosmic strings with such values of Gรยผ would be beyond the reach of LIGO, but could be measured by other planned and proposed detectors such as SKA, LISA, TianQin, AION-1km, AEDGE, Einstein Telescope and Cosmic Explorer. If this interpretation is confirmed future GW measurements would also allow us to probe the expansion history of the Universe to times much before what we can infer from the currently known data.
[please email a.held@imperial.ac.uk for zoom link or password]
The NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gรยผรขหห(4รโ10^{รขหโ11},10^{รขหโ10}) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers. The SGWB produced by cosmic strings with such values of Gรยผ would be beyond the reach of LIGO, but could be measured by other planned and proposed detectors such as SKA, LISA, TianQin, AION-1km, AEDGE, Einstein Telescope and Cosmic Explorer. If this interpretation is confirmed future GW measurements would also allow us to probe the expansion history of the Universe to times much before what we can infer from the currently known data.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
29 Mar 2021
Lonti: A crash course on the superconformal index
Costis Papageorgakis
(QMUL)
Abstract:
This is the live session included as part of the LonTI lecture on the Superconformal Index. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.
This is the live session included as part of the LonTI lecture on the Superconformal Index. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.
The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.
Posted by: pethybridge
Thu
25 Mar 2021
Another dimension of Kerr
Donal O'Connell
(Edinburgh U.)
Abstract:
[there will be a 30min pre-seminar for students. For zoom link, please contact s.nagyATqmul.ac.uk]
Abstract: Recent work has broadened the scope of scattering amplitudes to include large, classical objects such as the Kerr black hole. This new perspective illuminates surprising aspects of classical gravity, such as the Newman-Janis shift relating Kerr to Schwarzschild. I will describe the connection between amplitudes and classical physics, focussing on the case of Kerr.
[there will be a 30min pre-seminar for students. For zoom link, please contact s.nagyATqmul.ac.uk]
Abstract: Recent work has broadened the scope of scattering amplitudes to include large, classical objects such as the Kerr black hole. This new perspective illuminates surprising aspects of classical gravity, such as the Newman-Janis shift relating Kerr to Schwarzschild. I will describe the connection between amplitudes and classical physics, focussing on the case of Kerr.
Posted by: QMW
Thu
25 Mar 2021
Confining or Not?
Igor Klebanov
(Princeton University)
Abstract:
The problem of Color Confinement in Yang-Mills theory is one of the deepest problems in theoretical physics. There is convincing numerical evidence from Lattice Gauge Theory, yet the proof of Confinement in Asymptotically Free theories has not been found. I will briefly introduce the Confinement problem and review some results on large N theories using the gauge/gravity duality. I will then discuss two-dimensional SU(N) theory coupled to an adjoint Majorana fermion. I will show that, when the adjoint mass is sent to zero, the spectrum retains a mass gap but the confinement disappears. Using the Discretized Light-Cone Quantization, I will discuss the spectrum of color singlet states and exhibit certain threshold states. Similar threshold states are also present in a model with a massless adjoint and a massive fundamental fermion. They provide new evidence for the lack of confinement. When the adjoint mass is turned on, the theory becomes confining, and the spectrum of bound states becomes discrete. –– Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com/registration.html. The link will be emailed.
The problem of Color Confinement in Yang-Mills theory is one of the deepest problems in theoretical physics. There is convincing numerical evidence from Lattice Gauge Theory, yet the proof of Confinement in Asymptotically Free theories has not been found. I will briefly introduce the Confinement problem and review some results on large N theories using the gauge/gravity duality. I will then discuss two-dimensional SU(N) theory coupled to an adjoint Majorana fermion. I will show that, when the adjoint mass is sent to zero, the spectrum retains a mass gap but the confinement disappears. Using the Discretized Light-Cone Quantization, I will discuss the spectrum of color singlet states and exhibit certain threshold states. Similar threshold states are also present in a model with a massless adjoint and a massive fundamental fermion. They provide new evidence for the lack of confinement. When the adjoint mass is turned on, the theory becomes confining, and the spectrum of bound states becomes discrete. –– Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com/registration.html. The link will be emailed.
Posted by: andrea
Wed
24 Mar 2021
3d Large N vector models at the boundary.
๐ London
Lorenzo di Pietro
(University of Trieste)
Abstract:
In this talk I will discuss boundary RG flows for a 4d free scalar field coupled to large N vector models on a 3d boundary. These RG flows connect decoupled fixed points with the free and the critical vector model on the boundary, and they enjoy strong-weak dualities. I will also consider adding gauge fields to the setup.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
In this talk I will discuss boundary RG flows for a 4d free scalar field coupled to large N vector models on a 3d boundary. These RG flows connect decoupled fixed points with the free and the critical vector model on the boundary, and they enjoy strong-weak dualities. I will also consider adding gauge fields to the setup.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Wed
24 Mar 2021
Protected operator algebras and holography
Connor Behan
(Oxford)
Abstract:
Bootstrap methods have greatly expanded our ability to compute correlation functions in the supergravity approximation. As a result, we now know Mellin space expressions for general half-BPS four-point functions at tree-level in the main holographic CFTs with maximal supersymmetry. These are the \(\mathcal{N} = (2,0)\) theory in six dimensions, \(\mathcal{N} = 4\) Super Yang Mills in four dimensions and \(\mathcal{N} = 8\) ABJM theory in three dimensions. In all three cases, a rich subsector of operators that generate an infinite dimensional symmetry may be constructed by passing to the cohomology of a certain nilpotent supercharge. I will explain the main features of this construction and how they may be accessed holographically. When the protected operators generate a W-algebra, we will see that their four-point functions agree precisely with those predicted by AdS / CFT thus giving a complete check. The other possibility leads us to consider topological quantum mechanics where the calculations are more difficult. Nevertheless, I will show that an infinite family of special OPE coefficients obeys non-perturbative relations that follow from the one-dimensional theory.
https://zoom.us/j/96173937792?pwd=dHNkVVp0T0RtSitFZ2xaUkhqS1VjQT09
Bootstrap methods have greatly expanded our ability to compute correlation functions in the supergravity approximation. As a result, we now know Mellin space expressions for general half-BPS four-point functions at tree-level in the main holographic CFTs with maximal supersymmetry. These are the \(\mathcal{N} = (2,0)\) theory in six dimensions, \(\mathcal{N} = 4\) Super Yang Mills in four dimensions and \(\mathcal{N} = 8\) ABJM theory in three dimensions. In all three cases, a rich subsector of operators that generate an infinite dimensional symmetry may be constructed by passing to the cohomology of a certain nilpotent supercharge. I will explain the main features of this construction and how they may be accessed holographically. When the protected operators generate a W-algebra, we will see that their four-point functions agree precisely with those predicted by AdS / CFT thus giving a complete check. The other possibility leads us to consider topological quantum mechanics where the calculations are more difficult. Nevertheless, I will show that an infinite family of special OPE coefficients obeys non-perturbative relations that follow from the one-dimensional theory.
https://zoom.us/j/96173937792?pwd=dHNkVVp0T0RtSitFZ2xaUkhqS1VjQT09
Posted by: IC
Tue
23 Mar 2021
The Heavy Dark Matter Frontier
Filippo Sala
(LPTHE Paris)
Abstract:
I will motivate the possibility that particle Dark Matter (DM) is heavier than the so-called `unitarity limit', of about 100 TeV, and review the proposals to evade it. Among these proposals, I will focus on recent results on supercooled confining phase transitions in the early universe, whose implications are relevant beyond the DM problem. I will finally discuss how these scenarios will be probed at telescopes, underground labs, colliders and gravitational waves detectors.
[please email a.held@imperial.ac.uk for zoom link or password]
I will motivate the possibility that particle Dark Matter (DM) is heavier than the so-called `unitarity limit', of about 100 TeV, and review the proposals to evade it. Among these proposals, I will focus on recent results on supercooled confining phase transitions in the early universe, whose implications are relevant beyond the DM problem. I will finally discuss how these scenarios will be probed at telescopes, underground labs, colliders and gravitational waves detectors.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
22 Mar 2021
Lonti: A crash course on the superconformal index
Costis Papageorgakis
(QMUL)
Abstract:
This recorded tutorial is available via youtube at https://youtu.be/L-C6Xx0uI3c. The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.
This recorded tutorial is available via youtube at https://youtu.be/L-C6Xx0uI3c. The superconformal index is a very useful tool that allows us to probe the protected spectrum of a superconformal field theory (SCFT). After a brief review of the construction of unitary irreducible representations of the superconformal algebra, I will then motivate and give its definition for generic SCFTs before specialising to 4D N=2. Special limits of the index with additional supersymmetry, as well as applications will also be discussed. No prior knowledge of the topic is required.
Posted by: pethybridge
Mon
22 Mar 2021
Lonti: Entanglement in 1+1D Quantum Field Theory
Olalla Castro Alvaredo
(City)
Abstract:
This is the live session included as part of the LonTI lecture on Entanglement in 1+1D Quantum Field Theory. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
This is the live session included as part of the LonTI lecture on Entanglement in 1+1D Quantum Field Theory. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
Posted by: pethybridge
Thu
18 Mar 2021
TTbar-deformed conformal field theories out of equilibrium
Takato Yoshimura
(Tokyo Institute of Technology)
Abstract:
In this talk I will discuss the universal properties of transport phenomena in TTbar-deformed conformal field theories. TTbar-deformed CFTs are exactly solvable and admit a number of approaches, each of which is seemingly unrelated. Amongst them, for our purpose, which is to study transport phenomena in TTbar-deformed CFTs, we make use of the following: integrability and holography. I will apply these two approaches to study non-equilibrium steady states and Drude weights, finding perfect agreement. I will also discuss a curious connection between TTbar-deformed CFTs and an integrable cellular automaton model called the Rule 54 chain. –––- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
In this talk I will discuss the universal properties of transport phenomena in TTbar-deformed conformal field theories. TTbar-deformed CFTs are exactly solvable and admit a number of approaches, each of which is seemingly unrelated. Amongst them, for our purpose, which is to study transport phenomena in TTbar-deformed CFTs, we make use of the following: integrability and holography. I will apply these two approaches to study non-equilibrium steady states and Drude weights, finding perfect agreement. I will also discuss a curious connection between TTbar-deformed CFTs and an integrable cellular automaton model called the Rule 54 chain. –––- Part of the London Integrability Journal Club. If you are a new participant, please register at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
17 Mar 2021
D-instanton amplitude in string theory
Ashoke Sen
(HCRI)
Abstract:
D-instantons give non-perturbative contribution to string theory amplitudes which can be computed using world-sheet techniques. However the integrals that appear in this computation often have divergences from corners of the moduli spaces which cannot be tamed by the usual procedure of analytic continuation. We show how using insights from string field theory we can extract finite unambiguous results from these apparently divergent integrals.
The Zoom link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk
D-instantons give non-perturbative contribution to string theory amplitudes which can be computed using world-sheet techniques. However the integrals that appear in this computation often have divergences from corners of the moduli spaces which cannot be tamed by the usual procedure of analytic continuation. We show how using insights from string field theory we can extract finite unambiguous results from these apparently divergent integrals.
The Zoom link will be sent by your local Triangle seminar organiser or you can contact bogdan.stefanski.1@city.ac.uk
Posted by: CityU2
Tue
16 Mar 2021
Encoding the hologram into matrices
Masanori Hanada
( University of Surrey)
Abstract:
In holography, the geometry of gravitational theory should be encoded in its non-gravitational dual. In particular, in gauge/gravity duality, the geometry should be encoded into the color degrees of freedom (matrices) in U(N) supersymmetric Yang-Mills theory.
When the Yang-Mills theory is regarded as the low-energy effective theory of a system of N D-branes and open strings between them. Transverse spatial directions emerge from scalar fields, which are N*N matrices with color indices; roughly speaking, the eigenvalues are the locations of D-branes. In the past, it was argued that this simple 'emergent space' picture cannot be used in the context of gauge/gravity duality, because the ground-state wave function delocalizes at large N, leading to a conflict with the locality in the bulk geometry.
We show that this conventional wisdom is not correct: the ground-state wave function does not delocalize, and there is no conflict with the locality of the bulk geometry. This conclusion is obtained by clarifying the meaning of the 'diagonalization of a matrix' in Yang-Mills theory, which is not as obvious as one might think. This observation opens up the prospect of characterizing the bulk geometry via the color degrees of freedom in Yang-Mills theory, all the way down to the center of the bulk.
[please email a.held@imperial.ac.uk for zoom link or password]
In holography, the geometry of gravitational theory should be encoded in its non-gravitational dual. In particular, in gauge/gravity duality, the geometry should be encoded into the color degrees of freedom (matrices) in U(N) supersymmetric Yang-Mills theory.
When the Yang-Mills theory is regarded as the low-energy effective theory of a system of N D-branes and open strings between them. Transverse spatial directions emerge from scalar fields, which are N*N matrices with color indices; roughly speaking, the eigenvalues are the locations of D-branes. In the past, it was argued that this simple 'emergent space' picture cannot be used in the context of gauge/gravity duality, because the ground-state wave function delocalizes at large N, leading to a conflict with the locality in the bulk geometry.
We show that this conventional wisdom is not correct: the ground-state wave function does not delocalize, and there is no conflict with the locality of the bulk geometry. This conclusion is obtained by clarifying the meaning of the 'diagonalization of a matrix' in Yang-Mills theory, which is not as obvious as one might think. This observation opens up the prospect of characterizing the bulk geometry via the color degrees of freedom in Yang-Mills theory, all the way down to the center of the bulk.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
15 Mar 2021
Lonti: Entanglement in 1+1D Quantum Field Theory
Olalla Castro Alvaredo
(City)
Abstract:
This tutorial is available via youtube at https://youtu.be/zU-BRF6xLik. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
This tutorial is available via youtube at https://youtu.be/zU-BRF6xLik. In this short course I will introduce branch point twist fields and explain how they emerge in the context of computing entanglement measures in 1+1D.
I will focus on massive 1+1D integrable quantum field theory (IQFT) and also comment on some well-known results in conformal field theory (CFT).
The talk will be structured into three main parts:
First, I will introduce entanglement measures, focussing on the entanglement entropy, explain how these measures relate to partition functions in multi-sheeted Riemann surfaces and how these, in turn, may be expressed as correlators of branch point twist fields.
Second, I will show how several well-known results in CFT and IQFT are very easily derived in this branch point twist field picture and how they can also be recovered numerically in a quantum spin chain.
Finally, I will explain how more involved computations with branch point twist fields may be performed by exploiting form factor technology and will end the talk by showing an example of one such calculation.
Posted by: pethybridge
Mon
15 Mar 2021
Lonti: Gravity and black holes in AdS
Toby Wiseman
(IC)
Abstract:
This is the live session included as part of the LonTI lecture on Gravity and black holes in AdS. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
This is the live session included as part of the LonTI lecture on Gravity and black holes in AdS. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
Posted by: pethybridge
Thu
11 Mar 2021
QCD instantons and Hadron Colliders
Valentin Khoze
(Durham U.)
Abstract:
QCD instantons are arguably the best motivated yet unobserved nonperturbative effects predicted by the Standard Model. A discovery and detailed study of instanton-generated processes at colliders would provide a new window into the phenomenological exploration of QCD and a vastly improved fundamental understanding of its non-perturbative dynamics. We present for the first time a full calculation of QCD instanton-induced processes in proton-proton collisions accounting for quantum corrections due to both initial and final state gluon interactions. Although QCD instanton processes are predicted to be produced with a large scattering cross-section at small centre-of-mass partonic energies, discovering them at hadron colliders is a challenging task that requires dedicated search strategies.
[Based on https://arxiv.org/abs/2010.02287 and https://arxiv.org/abs/1911.09726.] [for zoom link contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
QCD instantons are arguably the best motivated yet unobserved nonperturbative effects predicted by the Standard Model. A discovery and detailed study of instanton-generated processes at colliders would provide a new window into the phenomenological exploration of QCD and a vastly improved fundamental understanding of its non-perturbative dynamics. We present for the first time a full calculation of QCD instanton-induced processes in proton-proton collisions accounting for quantum corrections due to both initial and final state gluon interactions. Although QCD instanton processes are predicted to be produced with a large scattering cross-section at small centre-of-mass partonic energies, discovering them at hadron colliders is a challenging task that requires dedicated search strategies.
[Based on https://arxiv.org/abs/2010.02287 and https://arxiv.org/abs/1911.09726.] [for zoom link contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Thu
11 Mar 2021
Lefschetz thimbles in sigma models
Nikita Nekrasov
(Stony Brook U., SCGP)
Abstract:
Two dimensional sigma models describe (harmonic) maps of Riemann surfaces to Riemannian manifolds. I will present the
motivations to study the complexification of this problem. I will present the novel approach, developed in my work with Igor Krichever, allowing to construct essentially all twisted complexified harmonic maps of two-torus to spheres and projective spaces. – Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.
Two dimensional sigma models describe (harmonic) maps of Riemann surfaces to Riemannian manifolds. I will present the
motivations to study the complexification of this problem. I will present the novel approach, developed in my work with Igor Krichever, allowing to construct essentially all twisted complexified harmonic maps of two-torus to spheres and projective spaces. – Part of the London Integrability Journal Club. If you are a new participant please register at integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
10 Mar 2021
The statistical mechanics of near-extremal and near-BPS black holes
๐ London
Luca Iliesiu
(Stanford University)
Abstract:
An important open question in black hole thermodynamics is about the existence of a "mass gap" between an extremal black hole and the lightest near-extremal state within a sector of fixed charge. In this talk, I will discuss how to reliably compute the partition function of 4d Reissner-Nordstrom near-extremal black holes at temperature scales comparable to the conjectured gap. I will show that the density of states at fixed charge does not exhibit a gap in the simplest gravitational non-supersymmetric theories; rather, at the expected gap energy scale, we see a continuum of states whose meaning we will extensively discuss. Finally, I will present a similar computation for nearly-BPS black holes in 4d N=2 supergravity. As opposed to their non-supersymmetric counterparts, such black holes do in fact exhibit a gap consistent with various string theory predictions. [please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
An important open question in black hole thermodynamics is about the existence of a "mass gap" between an extremal black hole and the lightest near-extremal state within a sector of fixed charge. In this talk, I will discuss how to reliably compute the partition function of 4d Reissner-Nordstrom near-extremal black holes at temperature scales comparable to the conjectured gap. I will show that the density of states at fixed charge does not exhibit a gap in the simplest gravitational non-supersymmetric theories; rather, at the expected gap energy scale, we see a continuum of states whose meaning we will extensively discuss. Finally, I will present a similar computation for nearly-BPS black holes in 4d N=2 supergravity. As opposed to their non-supersymmetric counterparts, such black holes do in fact exhibit a gap consistent with various string theory predictions. [please email alejandro.cabo_bizet@kcl.ac.uk for the zoom link]
Posted by: andrea
Wed
10 Mar 2021
Attractor indices, brane tilings and crystals
Boris Pioline
(LPTHE Jussieu)
Abstract:
In type II strings compactified on a Calabi-Yau threefold \(X\), the Donaldson-Thomas (DT) invariants \(\Omega(\gamma,z)\) counting
BPS black holes have an intricate dependence on the moduli \(z\), due to wall-crossing phenomena. When \(X\) is a toric threefold,
these indices are related to the DT invariants of a quiver with potential with superpotential, encoded by a brane tiling.
I will present a conjecture for the DT invariants for all dimension vectors \(d\) in a certain chamber \(z_*(d)\) known
as the attractor (or self-stability) chamber. In short, "DT invariants all vanish, except when they are known not to."
In combination with the attractor flow tree formulae, this conjecture provides an algorithmic way of computing the DT invariants \(\Omega(\gamma,z)\) for any \(\gamma,z\). The conjecture is supported by a large number of checks, including a successful comparison with the Vafa-Witten invariants of a Fano surface \(S\) when \(X\) is the total space of the canonical bundle \(K_S\), and with the counting of molten crystals for framed DT invariants in the non-commutative chamber. Based on works with G. Beaujard, J. Manschot and S. Mozgovoy, arXiv:2004.14466 and 2012.14358
Join Zoom Meeting
https://zoom.us/j/94029175955?pwd=b1hvVnVxbFZjTmM5bkxaWi93VkpzUT09
Meeting ID: 940 2917 5955
Passcode: 086150
In type II strings compactified on a Calabi-Yau threefold \(X\), the Donaldson-Thomas (DT) invariants \(\Omega(\gamma,z)\) counting
BPS black holes have an intricate dependence on the moduli \(z\), due to wall-crossing phenomena. When \(X\) is a toric threefold,
these indices are related to the DT invariants of a quiver with potential with superpotential, encoded by a brane tiling.
I will present a conjecture for the DT invariants for all dimension vectors \(d\) in a certain chamber \(z_*(d)\) known
as the attractor (or self-stability) chamber. In short, "DT invariants all vanish, except when they are known not to."
In combination with the attractor flow tree formulae, this conjecture provides an algorithmic way of computing the DT invariants \(\Omega(\gamma,z)\) for any \(\gamma,z\). The conjecture is supported by a large number of checks, including a successful comparison with the Vafa-Witten invariants of a Fano surface \(S\) when \(X\) is the total space of the canonical bundle \(K_S\), and with the counting of molten crystals for framed DT invariants in the non-commutative chamber. Based on works with G. Beaujard, J. Manschot and S. Mozgovoy, arXiv:2004.14466 and 2012.14358
Join Zoom Meeting
https://zoom.us/j/94029175955?pwd=b1hvVnVxbFZjTmM5bkxaWi93VkpzUT09
Meeting ID: 940 2917 5955
Passcode: 086150
Posted by: IC
Tue
9 Mar 2021
From density peaks to Dark Matter halos
Marcello Musso
(ICTP-EAIFR and MPIA Munich)
Abstract:
Analytical models of structure formation are an important tool, complementary to N-body simulations, to investigate the formation of cosmic structures and the dependence of their statistics on cosmological parameters. They rely on some non-linear map, typically spherical collapse, to relate topological features of the initial density field (number of maxima, minima, saddles, critical points...) to different types of structures and events (halos, voids, filaments, mergers...) in the cosmic web.
I will give a broad introduction to the topic and discuss some recent developments.
[please email a.held@imperial.ac.uk for zoom link or password]
Analytical models of structure formation are an important tool, complementary to N-body simulations, to investigate the formation of cosmic structures and the dependence of their statistics on cosmological parameters. They rely on some non-linear map, typically spherical collapse, to relate topological features of the initial density field (number of maxima, minima, saddles, critical points...) to different types of structures and events (halos, voids, filaments, mergers...) in the cosmic web.
I will give a broad introduction to the topic and discuss some recent developments.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
8 Mar 2021
Lonti: Gravity and black holes in AdS
Toby Wiseman
(IC)
Abstract:
The release of the youtube video for the London Theory institute seminar series available at https://youtu.be/jtfmWDrC370. Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
The release of the youtube video for the London Theory institute seminar series available at https://youtu.be/jtfmWDrC370. Gravity in asymptotic AdS spacetimes behaves in many ways quite differently to the usual asymptotically flat situation we are usually introduced to. It is very important in understanding the AdS-CFT correspondence, and many of these differences to the flat setting have important implications. In this lecture and the problem sheet I will introduce AdS spacetime, asymptotic AdS spacetimes and then focus on the physics of black holes in AdS. For the simplest static black holes we will explore their behaviour, the implications for AdS-CFT and introduce some basic calculational tools to study them.
Posted by: pethybridge
Mon
8 Mar 2021
Lonti: From spin chain to AdS/CFT with Mathematica
Nikolay Gromov
(KCL)
Abstract:
This is the live session included as part of the LonTI lecture on "From spin chain to AdS/CFT with Mathematica". Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. รขโฌโนIn this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system. Some examples are given with simple Mathematica code. We also discuss applications to AdS/CFT correspondence.
This is the live session included as part of the LonTI lecture on "From spin chain to AdS/CFT with Mathematica". Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom. รขโฌโนIn this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system. Some examples are given with simple Mathematica code. We also discuss applications to AdS/CFT correspondence.
Posted by: pethybridge
Thu
4 Mar 2021
Ten dimensional hidden symmetry of N=4 SYM
Frank Coronado
(McGill University)
Abstract:
I will present a generating function for the loop-integrands of all four-point functions of protected single-trace operators in \(\mathcal{N}=4\) SYM. This function enjoys a ten-dimensional symmetry that combines spacetime and the internal R-charge symmetries. By considering a 10D light-like limit I will establish a relationship between the simplest four-point correlators (octagons) and four-particle amplitudes. –- Part of the London Integrability Journal Club. If you are a new participant, please register using the form at
integrability-london.weebly.com. The link will be emailed.
I will present a generating function for the loop-integrands of all four-point functions of protected single-trace operators in \(\mathcal{N}=4\) SYM. This function enjoys a ten-dimensional symmetry that combines spacetime and the internal R-charge symmetries. By considering a 10D light-like limit I will establish a relationship between the simplest four-point correlators (octagons) and four-particle amplitudes. –- Part of the London Integrability Journal Club. If you are a new participant, please register using the form at
integrability-london.weebly.com. The link will be emailed.
Posted by: andrea
Wed
3 Mar 2021
Where is String Theory?
๐ London
Pedro Vieira
(Perimeter Institute)
Abstract:
The S-matrix bootstrap can be used to carve out the space of physical theories. What can we say about the space of theories of quantum gravity based on this approach? Based on work with Andrea Guerrieri and Joao Penedones. Zoom link: https://zoom.us/j/94504664165?pwd=c3VmMDNsbkRwWWdoUUxIRDhUcjB4dz09 (for password email dionysios.anninos@kcl.ac.uk)
The S-matrix bootstrap can be used to carve out the space of physical theories. What can we say about the space of theories of quantum gravity based on this approach? Based on work with Andrea Guerrieri and Joao Penedones. Zoom link: https://zoom.us/j/94504664165?pwd=c3VmMDNsbkRwWWdoUUxIRDhUcjB4dz09 (for password email dionysios.anninos@kcl.ac.uk)
Posted by: oxford
Wed
3 Mar 2021
Hyperbolic compactification of M-theory and de Sitter quantum gravity
๐ London
Gonzalo Torroba
(Centro Atomico Bariloche )
Abstract:
In this talk we will present a mechanism for accelerated expansion of the universe in the generic case of negative-curvature compactifications of M-theory, with minimal ingredients. M-theory on a hyperbolic manifold with small closed geodesics supporting Casimir energy, along with a single classical source (7-form flux), contains a 3-term structure for volume stabilization at positive potential energy. We find that a combination of warping and hyperbolic rigidity effects can stabilize the metric and form field. A simple generalization incorporating 4-form flux produces axion monodromy inflation, along with other forms of accelerated expansion. Our approach provides a simple uplift of the large-N M2-brane theory to de Sitter, and introduces new connections between mathematics and the physics of string/M theory compactifications. Zoom link: https://zoom.us/j/94504664165?pwd=c3VmMDNsbkRwWWdoUUxIRDhUcjB4dz09 (for password email dionysios.anninos@kcl.ac.uk)
In this talk we will present a mechanism for accelerated expansion of the universe in the generic case of negative-curvature compactifications of M-theory, with minimal ingredients. M-theory on a hyperbolic manifold with small closed geodesics supporting Casimir energy, along with a single classical source (7-form flux), contains a 3-term structure for volume stabilization at positive potential energy. We find that a combination of warping and hyperbolic rigidity effects can stabilize the metric and form field. A simple generalization incorporating 4-form flux produces axion monodromy inflation, along with other forms of accelerated expansion. Our approach provides a simple uplift of the large-N M2-brane theory to de Sitter, and introduces new connections between mathematics and the physics of string/M theory compactifications. Zoom link: https://zoom.us/j/94504664165?pwd=c3VmMDNsbkRwWWdoUUxIRDhUcjB4dz09 (for password email dionysios.anninos@kcl.ac.uk)
Posted by: oxford
Tue
2 Mar 2021
PBHs and Gravitational Waves
Antonio Riotto
(Geneva University)
Abstract:
We will discuss the relation between primordial black holes and gravitational waves in the view of the recent Ligo/Virgo and NanoGrav data.
[please email a.held@imperial.ac.uk for zoom link or password]
We will discuss the relation between primordial black holes and gravitational waves in the view of the recent Ligo/Virgo and NanoGrav data.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Mon
1 Mar 2021
Lonti: From spin chain to AdS/CFT with Mathematica
Nikolay Gromov
(KCL)
Abstract:
The release of the youtube video for the London Theory institute seminar series https://youtu.be/jTRQTwBX9ek. In this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system.
Some examples are given with simple Mathematica code.
We also discuss applications to AdS/CFT correspondence.
Some derivations are formulated in the form of step-by-step exercises.
They can be solved either with Mathematica or by hand.
A quick introduction to Mathematica is provided in a separate video.
The release of the youtube video for the London Theory institute seminar series https://youtu.be/jTRQTwBX9ek. In this introductory lecture we describe the XXX Heisenberg spin chain, study its spectrum, wavefunctions and discuss integrability of the system.
Some examples are given with simple Mathematica code.
We also discuss applications to AdS/CFT correspondence.
Some derivations are formulated in the form of step-by-step exercises.
They can be solved either with Mathematica or by hand.
A quick introduction to Mathematica is provided in a separate video.
Posted by: pethybridge
February 2021
Thu
25 Feb 2021
Energy correlations at conformal collider
Gregory Korchemsky
(IPhT Saclay)
Abstract:
[For zoom link please contact s.nagyATqmul.ac.uk. There will be a pre-seminar for students at 13:30]
The energy-energy correlation (EEC) measures the angular distribution of the energy that flows through two calorimeters separated by some relative angle in the final state created by a source. We present a new approach to computing this observable that exploits the relation between the energy correlations and four-point correlation functions of conserved currents. In the limit of small and large angles, when
EEC describes the correlation between particles belonging, respectively, to the same jet and to
two almost back-to-back jets, we obtain a concise representation
of the EEC in terms of the conformal data of twist-two operators and verify it by comparing with
the results of explicit calculation at next-to-next-to-leading order in maximally supersymmetric
Yang-Mills theory. As a byproduct of our analysis, we predict the maximal weight part of the
analogous QCD expression.
[For zoom link please contact s.nagyATqmul.ac.uk. There will be a pre-seminar for students at 13:30]
The energy-energy correlation (EEC) measures the angular distribution of the energy that flows through two calorimeters separated by some relative angle in the final state created by a source. We present a new approach to computing this observable that exploits the relation between the energy correlations and four-point correlation functions of conserved currents. In the limit of small and large angles, when
EEC describes the correlation between particles belonging, respectively, to the same jet and to
two almost back-to-back jets, we obtain a concise representation
of the EEC in terms of the conformal data of twist-two operators and verify it by comparing with
the results of explicit calculation at next-to-next-to-leading order in maximally supersymmetric
Yang-Mills theory. As a byproduct of our analysis, we predict the maximal weight part of the
analogous QCD expression.
Posted by: QMW
Thu
25 Feb 2021
Integrable E-models, 4d Chern-Simons theory and affine Gaudin models
Benoit Vicedo
(University of York)
Abstract:
Two-dimensional integrable field theories are characterised by the existence of infinitely many integrals of motion. Recently, two unifying frameworks for describing such theories have emerged, based on four-dimensional Chern-Simons theory in the presence of surface defects and on Gaudin models associated with affine Kac-Moody algebras. I will explain how these formalisms can be used to construct infinite families of two-dimensional integrable field theories. The latter can all naturally be formulated as so-called E-models, a framework for describing Poisson-Lie T-duality in sigma-models. The talk will be based on the joint work [arXiv:2008.01829] with M. Benini and A. Schenkel and [2011.13809] with S. Lacroix. –– Please register using the form at integrability-london.weebly.com if you are a new participant. The link will be emailed.
Two-dimensional integrable field theories are characterised by the existence of infinitely many integrals of motion. Recently, two unifying frameworks for describing such theories have emerged, based on four-dimensional Chern-Simons theory in the presence of surface defects and on Gaudin models associated with affine Kac-Moody algebras. I will explain how these formalisms can be used to construct infinite families of two-dimensional integrable field theories. The latter can all naturally be formulated as so-called E-models, a framework for describing Poisson-Lie T-duality in sigma-models. The talk will be based on the joint work [arXiv:2008.01829] with M. Benini and A. Schenkel and [2011.13809] with S. Lacroix. –– Please register using the form at integrability-london.weebly.com if you are a new participant. The link will be emailed.
Posted by: andrea
Wed
24 Feb 2021
Causal symmetry breaking: from quantum chaos to wormholes
๐ London
Julian Sonner
(University of Geneva)
Abstract:
Quantum chaotic systems are often defined via the assertion that their spectral statistics coincides with, or is well approximated by, random matrix theory. In this talk I will explain how the universal content of random matrix theory emerges as the consequence of a simple symmetry-breaking principle and its associated Goldstone modes. This approach gives a natural way to identify wormhole-like correlations, even for individual theories, in particular in theories with gravity duals.
I will also discuss how to extend the Goldstone effective-field-theory approach to study operator correlation functions, and explain the relation of the EFT of quantum chaos to the bulk physics of wormhole-like geometries.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Quantum chaotic systems are often defined via the assertion that their spectral statistics coincides with, or is well approximated by, random matrix theory. In this talk I will explain how the universal content of random matrix theory emerges as the consequence of a simple symmetry-breaking principle and its associated Goldstone modes. This approach gives a natural way to identify wormhole-like correlations, even for individual theories, in particular in theories with gravity duals.
I will also discuss how to extend the Goldstone effective-field-theory approach to study operator correlation functions, and explain the relation of the EFT of quantum chaos to the bulk physics of wormhole-like geometries.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Posted by: andrea
Wed
24 Feb 2021
Quantum Field Theory and Beyond
Nathan Seiberg
(IAS)
Abstract:
The first talk will be general, i.e., at a colloquium level. The second talk will be more technical, i.e., at a seminar level. Yet, each of the two talks will be self-contained. For this reason, there will be some overlap between them.
Talk 1: Quantum Field Theory and Beyond
We will review the status of Quantum Field Theory (QFT) and will present it as รขโฌลthe language of physics.รขโฌย Using examples from string theory and condensed matter physics, we will motivate the fact that the standard framework of QFT should be extended. As specific examples, we will review the phenomena of fractons, which do not seem to fit the standard framework of continuum QFT. We will then present recent attempts to incorporate fractons in a slightly generalized version of quantum field theory.
Talk 2: Fractons: going beyond standard QFT
Starting with a lattice system at short distances, its long-distance behavior is captured by a continuum Quantum Field Theory (QFT). This description is universal, i.e., it is independent of most of the details of the microscopic system. Surprisingly, certain recently discovered lattice systems, and in particular models of fractons, seem to violate this general dogma. Motivated by this apparent contradiction, we will present exotic continuum QFTs that describe these systems.
The first talk will be general, i.e., at a colloquium level. The second talk will be more technical, i.e., at a seminar level. Yet, each of the two talks will be self-contained. For this reason, there will be some overlap between them.
Talk 1: Quantum Field Theory and Beyond
We will review the status of Quantum Field Theory (QFT) and will present it as รขโฌลthe language of physics.รขโฌย Using examples from string theory and condensed matter physics, we will motivate the fact that the standard framework of QFT should be extended. As specific examples, we will review the phenomena of fractons, which do not seem to fit the standard framework of continuum QFT. We will then present recent attempts to incorporate fractons in a slightly generalized version of quantum field theory.
Talk 2: Fractons: going beyond standard QFT
Starting with a lattice system at short distances, its long-distance behavior is captured by a continuum Quantum Field Theory (QFT). This description is universal, i.e., it is independent of most of the details of the microscopic system. Surprisingly, certain recently discovered lattice systems, and in particular models of fractons, seem to violate this general dogma. Motivated by this apparent contradiction, we will present exotic continuum QFTs that describe these systems.
Posted by: IC
Tue
23 Feb 2021
Gravitational waves from first order phase transitions in the early universe
Mark Hindmarsh
(University of Sussex)
Abstract:
Gravitational waves are expected to be an important probe of physics beyond the Standard Model, through their production at first order phase transitions. I will report on recent work on characterising the gravitational wave power spectrum, and outline some BSM physics which might be probed at the future space-based gravitational wave detector LISA.
[please email a.held@imperial.ac.uk for zoom link or password]
Gravitational waves are expected to be an important probe of physics beyond the Standard Model, through their production at first order phase transitions. I will report on recent work on characterising the gravitational wave power spectrum, and outline some BSM physics which might be probed at the future space-based gravitational wave detector LISA.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
18 Feb 2021
Conformal Fourier Analysis and Gaudin Integrability
Volker Schomerus
(Desy)
Abstract:
Conformal partial wave expansion provide Fourier-like decompositions of correlation functions in Conformal Field Theory. Despite their fundamental importance, conformal
partial waves remain poorly understood, at least beyond the case of four local fields.
In the last few years, a deep relation with integrable quantum mechanical models has emerged. It offers a wealth of powerful new algebraic methods to study and construct conformal partial waves e.g. for general supermultiplets, non-local (line-, surface-) operators and multi-point correlation functions. In my talk I will use ideas from harmonic analysis of the conformal group to embed conformal partial waves into the
framework of Gaudin integrable models and then discuss several concrete ramifications as trigonometric and elliptic Calogero-Sutherland models. The latter are relevant for multi-point blocks of scalar fields. ––- Part of London Integrability Journal Club. Please register at integrability-london.weebly.com/registration.html if you are a new participant.
Conformal partial wave expansion provide Fourier-like decompositions of correlation functions in Conformal Field Theory. Despite their fundamental importance, conformal
partial waves remain poorly understood, at least beyond the case of four local fields.
In the last few years, a deep relation with integrable quantum mechanical models has emerged. It offers a wealth of powerful new algebraic methods to study and construct conformal partial waves e.g. for general supermultiplets, non-local (line-, surface-) operators and multi-point correlation functions. In my talk I will use ideas from harmonic analysis of the conformal group to embed conformal partial waves into the
framework of Gaudin integrable models and then discuss several concrete ramifications as trigonometric and elliptic Calogero-Sutherland models. The latter are relevant for multi-point blocks of scalar fields. ––- Part of London Integrability Journal Club. Please register at integrability-london.weebly.com/registration.html if you are a new participant.
Posted by: andrea
Thu
18 Feb 2021
OPE for form factors
Amit Sever
(Tel Aviv U.)
Abstract:
We propose an operator product expansion for planar form factors of local operators in N = 4 SYM theory. This expansion is based on the dual conformal symmetry of these objects or, equivalently, the conformal symmetry of their dual description in terms of periodic Wilson loops. A form factor is decomposed into a sequence of known pentagon transitions and a new universal object that we call the รขโฌลform factor transitionรขโฌย. This transition is subject to a set of non-trivial bootstrap constraints, which allows us to bootstrap it at any value of the coupling. We evaluate the form factor transition for MHV form factors of the chiral half of the stress tensor supermultiplet at leading order in perturbation theory and use it to produce OPE predictions at any loop order. We match the one-loop and two-loop predictions with data available in the literature. [for zoom link contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
We propose an operator product expansion for planar form factors of local operators in N = 4 SYM theory. This expansion is based on the dual conformal symmetry of these objects or, equivalently, the conformal symmetry of their dual description in terms of periodic Wilson loops. A form factor is decomposed into a sequence of known pentagon transitions and a new universal object that we call the รขโฌลform factor transitionรขโฌย. This transition is subject to a set of non-trivial bootstrap constraints, which allows us to bootstrap it at any value of the coupling. We evaluate the form factor transition for MHV form factors of the chiral half of the stress tensor supermultiplet at leading order in perturbation theory and use it to produce OPE predictions at any loop order. We match the one-loop and two-loop predictions with data available in the literature. [for zoom link contact jung-wook(dot)kim(at)qmul(dot)ac(dot)uk]
Posted by: QMW
Wed
17 Feb 2021
Bootstrapping BPS algebras from colored crystals
๐ London
Wei Li
(Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing.)
Abstract:
I will explain a method of constructing BPS algebras for string theory on generic toric Calabi-Yau threefolds. The approach is a ``bootstrapรขโฌย method based on the 3D colored crystals that describe BPS states of the system. The resulting algebras are quiver Yangians Y(Q,W) that are associated with the quiver and the superpotential of the theory. [Please email alejandro.cabo_bizet@kcl.ac.uk for zoom link]
I will explain a method of constructing BPS algebras for string theory on generic toric Calabi-Yau threefolds. The approach is a ``bootstrapรขโฌย method based on the 3D colored crystals that describe BPS states of the system. The resulting algebras are quiver Yangians Y(Q,W) that are associated with the quiver and the superpotential of the theory. [Please email alejandro.cabo_bizet@kcl.ac.uk for zoom link]
Posted by: andrea
Tue
16 Feb 2021
Emergent gravity from hidden sectors and TT deformations
Elias Kiritsis
(APC, Paris)
Abstract:
We investigate emergent gravity extending the paradigm of the AdS/CFT correspondence. The emergent graviton is associated to the (dynamical) expectation value of the energy-momentum tensor. We derive the general effective description of such dynamics, and apply it to the case where a hidden theory generates gravity that is coupled to the Standard Model. In the linearized description, generically, such gravity is massive with the presence of an extra scalar degree of freedom. The propagators of both the spin-two and spin-zero modes are positive and well defined. The associated emergent gravitational theory is a bi-gravity theory, as is (secretly) the case in holography. The background metric on which the QFTs are defined, plays the role of dark energy and the emergent theory has always as a solution the original background metric. In the case where the hidden theory is holographic, the overall description yields a higher-dimensional bulk theory coupled to a brane. The effective graviton on the brane has four-dimensional characteristics both in the UV and IR and is always massive.
[please email a.held@imperial.ac.uk for zoom link or password]
We investigate emergent gravity extending the paradigm of the AdS/CFT correspondence. The emergent graviton is associated to the (dynamical) expectation value of the energy-momentum tensor. We derive the general effective description of such dynamics, and apply it to the case where a hidden theory generates gravity that is coupled to the Standard Model. In the linearized description, generically, such gravity is massive with the presence of an extra scalar degree of freedom. The propagators of both the spin-two and spin-zero modes are positive and well defined. The associated emergent gravitational theory is a bi-gravity theory, as is (secretly) the case in holography. The background metric on which the QFTs are defined, plays the role of dark energy and the emergent theory has always as a solution the original background metric. In the case where the hidden theory is holographic, the overall description yields a higher-dimensional bulk theory coupled to a brane. The effective graviton on the brane has four-dimensional characteristics both in the UV and IR and is always massive.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
11 Feb 2021
Knot Theory and Machine Learning
Fabian Ruhle
(CERN)
Abstract:
[For zoom details please email s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13:30]
Knot theory plays an important role in physics, mathematics and biology. Characterizing knots is, however, a difficult task. There are different ways to represent a knot (e.g. via braids, Gauss codes, Dowker-Thistlethwaite notation), and many knot invariants exist (e.g. the Alexander polynomial, Jones polynomial, determinant, slice genus). However, it is not known whether these can be used to identify a trivial knot, the so-called unknot.
We use different machine learning techniques to tackle this question. First, we use a very recent neural network architecture developed for natural language processing, called the reformer, to decide whether a given knot is the unknot. We also apply Reinforcement Learning to solve the harder problem of finding a set of Reidemeister/Markov moves that explicitly simplify a given knot as much as possible. If the algorithm finds a sequence of moves that removes all crossings of a knot in a given representation, then this knot is provably the unknot.
[For zoom details please email s.nagyATqmul.ac.uk There will be a pre-seminar for students at 13:30]
Knot theory plays an important role in physics, mathematics and biology. Characterizing knots is, however, a difficult task. There are different ways to represent a knot (e.g. via braids, Gauss codes, Dowker-Thistlethwaite notation), and many knot invariants exist (e.g. the Alexander polynomial, Jones polynomial, determinant, slice genus). However, it is not known whether these can be used to identify a trivial knot, the so-called unknot.
We use different machine learning techniques to tackle this question. First, we use a very recent neural network architecture developed for natural language processing, called the reformer, to decide whether a given knot is the unknot. We also apply Reinforcement Learning to solve the harder problem of finding a set of Reidemeister/Markov moves that explicitly simplify a given knot as much as possible. If the algorithm finds a sequence of moves that removes all crossings of a knot in a given representation, then this knot is provably the unknot.
Posted by: QMW
Thu
11 Feb 2021
Modeling finite-entropy states with free fermions
Oleksandr Gamayun
(University of Amsterdam)
Abstract:
The behavior of dynamical correlation functions in one-dimensional quantum systems at zero temperature is now very well understood in terms of linear and non-linear Luttinger models. The "microscopic" justification of these models consists in exactly accounting for the soft-mode excitations around the vacuum state and at most a few high-energy excitations. At finite temperature, or more generically for finite entropy states, this direct approach is not strictly applicable due to the different structure of soft excitations. To address these issues we study the asymptotic behavior of correlation functions in one-dimensional free fermion models. On the one hand, we obtain exact answers in terms of Fredholm determinants. On the other hand, based on "microscopic" numerical resummations, we develop a phenomenological approach that provides results depending only on the state-dependent dressing of the scattering phase. Our main example will be the sine-kernel and correlation functions in XY model.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
The behavior of dynamical correlation functions in one-dimensional quantum systems at zero temperature is now very well understood in terms of linear and non-linear Luttinger models. The "microscopic" justification of these models consists in exactly accounting for the soft-mode excitations around the vacuum state and at most a few high-energy excitations. At finite temperature, or more generically for finite entropy states, this direct approach is not strictly applicable due to the different structure of soft excitations. To address these issues we study the asymptotic behavior of correlation functions in one-dimensional free fermion models. On the one hand, we obtain exact answers in terms of Fredholm determinants. On the other hand, based on "microscopic" numerical resummations, we develop a phenomenological approach that provides results depending only on the state-dependent dressing of the scattering phase. Our main example will be the sine-kernel and correlation functions in XY model.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: andrea
Wed
10 Feb 2021
Adventures in Machine Learning and Theoretical Physics
๐ London
Thomas Fischbacher
(Google Research)
Abstract:
Machine Learning has opened many new doors in science across multiple
disciplines. Starting from recent work by the speaker and collaborators
on in-depth explorations into the vacuum structure of gauged maximal
supergravities using Machine Learning Technology, notably Google's
TensorFlow library, we subsequently take a broader perspective
on what happens when Machine Learning meets Physics. [Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Machine Learning has opened many new doors in science across multiple
disciplines. Starting from recent work by the speaker and collaborators
on in-depth explorations into the vacuum structure of gauged maximal
supergravities using Machine Learning Technology, notably Google's
TensorFlow library, we subsequently take a broader perspective
on what happens when Machine Learning meets Physics. [Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Posted by: andrea
Wed
10 Feb 2021
AdS/CFT at Finite String Coupling and Modular Invariance
Shai Chester
(Weizmann Inst.)
Abstract:
We study the N = 4 SU(N) super-Yang-Mills stress tensor multiplet four-point function at large N and finite complexified Yang-Mills coupling tau, which is dual to the Type IIB graviton correlator on AdS_5 รโ S^5 at large string length and finite string coupling. The specific four-point functions we consider are integrated correlators obtained by taking various combinations of four derivatives of m, b, and tau of the sphere free energy deformed by mass m and squashing parameter b, which can be computed using supersymmetric localization. We show that at each order in 1/N, these quantities can be written in terms of modular invariants, such as the well studied non-Holomorphic Eisenstein series as well as some new generalizations thereof. These results reproduce known features of the low-energy expansion of the four-graviton amplitude in type IIB superstring theory in ten-dimensional flat space, which is the first check of AdS/CFT at finite string coupling, and have interesting implications for the structure of the analogous expansion in AdS_5 รโ S^5.
Zoom
Join Zoom Meeting
https://zoom.us/j/93725965823?pwd=Q2lmeEhjQnJmZUsxMkp2THdVZ1cxUT09
Meeting ID: 937 2596 5823
Passcode: 640955
We study the N = 4 SU(N) super-Yang-Mills stress tensor multiplet four-point function at large N and finite complexified Yang-Mills coupling tau, which is dual to the Type IIB graviton correlator on AdS_5 รโ S^5 at large string length and finite string coupling. The specific four-point functions we consider are integrated correlators obtained by taking various combinations of four derivatives of m, b, and tau of the sphere free energy deformed by mass m and squashing parameter b, which can be computed using supersymmetric localization. We show that at each order in 1/N, these quantities can be written in terms of modular invariants, such as the well studied non-Holomorphic Eisenstein series as well as some new generalizations thereof. These results reproduce known features of the low-energy expansion of the four-graviton amplitude in type IIB superstring theory in ten-dimensional flat space, which is the first check of AdS/CFT at finite string coupling, and have interesting implications for the structure of the analogous expansion in AdS_5 รโ S^5.
Zoom
Join Zoom Meeting
https://zoom.us/j/93725965823?pwd=Q2lmeEhjQnJmZUsxMkp2THdVZ1cxUT09
Meeting ID: 937 2596 5823
Passcode: 640955
Posted by: IC
Tue
9 Feb 2021
Superconformal index and gravitational path-integral
Francesco Benini
(SISSA, Trieste)
Abstract:
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS spacetimes. Black holes correspond to
ensembles of states in the boundary field theory. In the presence of
supersymmetry, we rephrase the problem of counting those states in
terms of a supersymmetric partition function: the superconformal
index. By performing a careful analysis of the index of 4d N=4 SU(N)
Super-Yang-Mills theory, with the help of a Bethe Ansatz approach, we
are able to exactly reproduce the Bekenstein-Hawking entropy of BPS
black holes in AdS5 x S5. The large N limit exhibits many competing
contributions, that we are able to identify with complex saddles of
the (putative) gravitational path-integral. Along the way we propose a
necessary condition for complex saddles to contribute, based on the
size of their non-perturbative corrections.
AdS/CFT provides a consistent non-perturbative definition of quantum
gravity in asymptotically AdS spacetimes. Black holes correspond to
ensembles of states in the boundary field theory. In the presence of
supersymmetry, we rephrase the problem of counting those states in
terms of a supersymmetric partition function: the superconformal
index. By performing a careful analysis of the index of 4d N=4 SU(N)
Super-Yang-Mills theory, with the help of a Bethe Ansatz approach, we
are able to exactly reproduce the Bekenstein-Hawking entropy of BPS
black holes in AdS5 x S5. The large N limit exhibits many competing
contributions, that we are able to identify with complex saddles of
the (putative) gravitational path-integral. Along the way we propose a
necessary condition for complex saddles to contribute, based on the
size of their non-perturbative corrections.
Posted by: IC
Thu
4 Feb 2021
Wilson-'t Hooft lines as transfer matrices
Junya Yagi
(Tsinghua)
Abstract:
Supersymmetric gauge theories in four dimensions have various interrelated connections to quantum integrable systems. I will present a new correspondence which identifies Wilson-'t Hooft lines in N=2 circular quiver theories with transfer matrices of trigonometric systems. I will explain how this correspondence is related to Costello's 4d Chern-Simons theory and other similar correspondences. This is based on my joint work with Kazunobu Maruyoshi and Toshihiro Ota.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Supersymmetric gauge theories in four dimensions have various interrelated connections to quantum integrable systems. I will present a new correspondence which identifies Wilson-'t Hooft lines in N=2 circular quiver theories with transfer matrices of trigonometric systems. I will explain how this correspondence is related to Costello's 4d Chern-Simons theory and other similar correspondences. This is based on my joint work with Kazunobu Maruyoshi and Toshihiro Ota.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: CityU2
Wed
3 Feb 2021
Quantum Information Theory of the Gravitational Anomaly
Simeon Hellerman
(Tokyo U., IPMU)
Abstract:
I will explain that the notion of quantum entanglement is not defined for gravitationally anomalous two-dimensional theories, because they do not admit a local tensor factorization of the Hilbert space into local Hilbert spaces. Qualitatively, the modular flow cannot act consistently and unitarily in a finite region, if there are different numbers of states with a given energy traveling in the two opposite directions. I will make this precise by decomposing it into two observations: First, a two-dimensional conformal field theory admits a consistent quantization on a space with boundary only if it is not anomalous. Second, a local tensor factorization always leads to a definition of consistent, unitary, energy-preserving boundary condition. As a corollary I will establish a generalization of the Nielsen-Ninomiya theorem to all two-dimensional unitary local quantum field theories: No continuum quantum field theory in two dimensions can admit a lattice regulator unless its gravitational anomaly vanishes. I will advocate that these points be used to reinterpret the gravitational anomaly quantum-information-theoretically, as a fundamental obstruction to the localization of quantum information.
[Zoom link: please ask your local triangle organizer]
I will explain that the notion of quantum entanglement is not defined for gravitationally anomalous two-dimensional theories, because they do not admit a local tensor factorization of the Hilbert space into local Hilbert spaces. Qualitatively, the modular flow cannot act consistently and unitarily in a finite region, if there are different numbers of states with a given energy traveling in the two opposite directions. I will make this precise by decomposing it into two observations: First, a two-dimensional conformal field theory admits a consistent quantization on a space with boundary only if it is not anomalous. Second, a local tensor factorization always leads to a definition of consistent, unitary, energy-preserving boundary condition. As a corollary I will establish a generalization of the Nielsen-Ninomiya theorem to all two-dimensional unitary local quantum field theories: No continuum quantum field theory in two dimensions can admit a lattice regulator unless its gravitational anomaly vanishes. I will advocate that these points be used to reinterpret the gravitational anomaly quantum-information-theoretically, as a fundamental obstruction to the localization of quantum information.
[Zoom link: please ask your local triangle organizer]
Posted by: QMW
Wed
3 Feb 2021
Islands in black holes and cosmology
Tom Hartman
(Cornell)
Abstract:
I will summarize recent developments on the information paradox involving "islands" and replica wormholes, and discuss the extent to which these ideas can be applied to cosmology.
[Zoom link: please ask your local triangle organizer]
I will summarize recent developments on the information paradox involving "islands" and replica wormholes, and discuss the extent to which these ideas can be applied to cosmology.
[Zoom link: please ask your local triangle organizer]
Posted by: QMW
Tue
2 Feb 2021
The Topology of Data: from String Theory to Cosmology to Phases of Matter
Gary Shiu
(University of Wisconsin)
Abstract:
We are faced with an explosion of data in many areas of physics, but very so often, it is not the size but the complexity of the data that makes extracting physics from big datasets challenging. As I will discuss in this talk, data has shape and the shape of data encodes the underlying physics. Persistent homology is a tool in computational topology developed for quantifying the shape of data. I will discuss three applications of topological data analysis: 1) identifying structure of the string landscape, 2) constraining primordial non-Gaussianity from CMB measurements and large scale structures data, and 3) detecting and classifying phases of matter. Persistent homology condenses these datasets into their most relevant (and interpretable) features, so that simple statistical pipelines are sufficient in these contexts. This suggests that TDA can be used in conjunction with machine learning algorithms and improves their architecture.
Based on https://arxiv.org/abs/2009.14231, https://arxiv.org/abs/2009.04819, https://arxiv.org/abs/1907.10072, https://arxiv.org/abs/1812.06960, https://arxiv.org/abs/1712.08159.
[please email a.held@imperial.ac.uk for zoom link or password]
We are faced with an explosion of data in many areas of physics, but very so often, it is not the size but the complexity of the data that makes extracting physics from big datasets challenging. As I will discuss in this talk, data has shape and the shape of data encodes the underlying physics. Persistent homology is a tool in computational topology developed for quantifying the shape of data. I will discuss three applications of topological data analysis: 1) identifying structure of the string landscape, 2) constraining primordial non-Gaussianity from CMB measurements and large scale structures data, and 3) detecting and classifying phases of matter. Persistent homology condenses these datasets into their most relevant (and interpretable) features, so that simple statistical pipelines are sufficient in these contexts. This suggests that TDA can be used in conjunction with machine learning algorithms and improves their architecture.
Based on https://arxiv.org/abs/2009.14231, https://arxiv.org/abs/2009.04819, https://arxiv.org/abs/1907.10072, https://arxiv.org/abs/1812.06960, https://arxiv.org/abs/1712.08159.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
January 2021
Thu
28 Jan 2021
Quantum Natural Language Processing on NISQ hardware
Konstantinos Meichanetzidis
(Oxford)
Abstract:
[Please inqure jung-wook(dot)kim(at)qmul(dot)ac(dot)uk for the zoom link]
Taking advantage of mathematical similarities between grammar models and quantum theory, we present a canonical way of instantiating grammatical sentences as quantum circuits. In the context of quantum machine learning, we define toy natural language processing tasks and implement them on readily accessible quantum processors, such as those provided by IBMQ.
[Please inqure jung-wook(dot)kim(at)qmul(dot)ac(dot)uk for the zoom link]
Taking advantage of mathematical similarities between grammar models and quantum theory, we present a canonical way of instantiating grammatical sentences as quantum circuits. In the context of quantum machine learning, we define toy natural language processing tasks and implement them on readily accessible quantum processors, such as those provided by IBMQ.
Posted by: QMW
Thu
28 Jan 2021
2D dilaton-gravity, matrix models, and the minimal string
Gustavo Turiaci
(UC Santa Barbara)
Abstract:
In the first part of this talk I will review the recent realization that a large class of two-dimensional theories of dilaton-gravity in asymptotically AdS space are holographically dual to a random matrix model. In this description the matrix represents a random boundary Hamiltonian, and its probability distribution depends on the dilaton potential in a specific way. In the second part of the talk I will explain the relation between two-dimensional dilaton-gravity and the minimal string theory.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
In the first part of this talk I will review the recent realization that a large class of two-dimensional theories of dilaton-gravity in asymptotically AdS space are holographically dual to a random matrix model. In this description the matrix represents a random boundary Hamiltonian, and its probability distribution depends on the dilaton potential in a specific way. In the second part of the talk I will explain the relation between two-dimensional dilaton-gravity and the minimal string theory.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: andrea
Wed
27 Jan 2021
Derivation of AdS/CFT for Vector Models
๐ London
Shai Chester
(Weizmann Institute)
Abstract:
We derive an explicit map between the singlet sector of the free and critical O(N) and U(N) vector models in any spacetime dimension above two and to all orders in 1/N, and a bulk higher spin theory in anti-de Sitter space in one higher dimension. For the boundary theory, we use the bilocal formalism of Jevicki et al to restrict to the singlet sector of the vector model. The bulk theory is defined from the boundary theory via our mapping and is a consistent quantum higher spin theory with a well defined action. Our mapping relates bilocal operators in the boundary theory to higher spin fields in the bulk, while single trace local operators in the boundary theory are related to boundary values of higher spin fields.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
We derive an explicit map between the singlet sector of the free and critical O(N) and U(N) vector models in any spacetime dimension above two and to all orders in 1/N, and a bulk higher spin theory in anti-de Sitter space in one higher dimension. For the boundary theory, we use the bilocal formalism of Jevicki et al to restrict to the singlet sector of the vector model. The bulk theory is defined from the boundary theory via our mapping and is a consistent quantum higher spin theory with a well defined action. Our mapping relates bilocal operators in the boundary theory to higher spin fields in the bulk, while single trace local operators in the boundary theory are related to boundary values of higher spin fields.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Posted by: andrea
Tue
26 Jan 2021
Scalar fields variations and the Swampland
Marco Scalisi
(Max Planck Institute for Physics)
Abstract:
The most famous slogan of the Swampland program is that not all effective field theories (EFTs) admit ultraviolet completion into quantum gravity. In this talk, we focus on the significance of this claim for EFTs which involve scalar field variations and on the implications for cosmology. To conclude, we examine some concrete string-phenomenological set-ups with warped throats.
[please email a.held@imperial.ac.uk for zoom link or password]
The most famous slogan of the Swampland program is that not all effective field theories (EFTs) admit ultraviolet completion into quantum gravity. In this talk, we focus on the significance of this claim for EFTs which involve scalar field variations and on the implications for cosmology. To conclude, we examine some concrete string-phenomenological set-ups with warped throats.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
21 Jan 2021
Unimodular vs Nilpotent Superfield Approach to Pure dS Supergravity
Sukruti Bansal
(Chulalongkorn University)
Abstract:
[there will be a 15 min pre-seminar for students. For zoom link, please email s.nagyATqmul.ac.uk]
Abstract: Recent progress in understanding de Sitter spacetime in supergravity and string theory has led to the development of a 4D supergravity with spontaneously broken supersymmetry allowing for de Sitter vacua, also called de Sitter supergravity. One approach makes use of constrained (nilpotent) superfields, while an alternative one couples supergravity to a locally supersymmetric generalization of the Volkov-Akulov goldstino action. These two approaches have been shown to give rise to the same 4D action.
A novel approach to de Sitter vacua in supergravity involves the generalisation of unimodular gravity to supergravity using a super-Stรยผckelberg mechanism. We make a connection between this new approach and the previous two. We show that upon appropriate field redefinitions, the 4D actions match up to the cubic order in the fields. This points at the possible existence of a more general framework to obtain de Sitter spacetimes from high-energy theories.
[there will be a 15 min pre-seminar for students. For zoom link, please email s.nagyATqmul.ac.uk]
Abstract: Recent progress in understanding de Sitter spacetime in supergravity and string theory has led to the development of a 4D supergravity with spontaneously broken supersymmetry allowing for de Sitter vacua, also called de Sitter supergravity. One approach makes use of constrained (nilpotent) superfields, while an alternative one couples supergravity to a locally supersymmetric generalization of the Volkov-Akulov goldstino action. These two approaches have been shown to give rise to the same 4D action.
A novel approach to de Sitter vacua in supergravity involves the generalisation of unimodular gravity to supergravity using a super-Stรยผckelberg mechanism. We make a connection between this new approach and the previous two. We show that upon appropriate field redefinitions, the 4D actions match up to the cubic order in the fields. This points at the possible existence of a more general framework to obtain de Sitter spacetimes from high-energy theories.
Posted by: QMW
Thu
21 Jan 2021
Overlaps and Fermionic Dualities for Integrable Super Spin Chains
Charlotte Kristjansen
(Niels Bohr Institute Copenhagen)
Abstract:
The \(\mathfrak{psu}(2,2|4)\) integrable super spin chain underlying the AdS/CFT correspondence has integrable boundary states which describe set-ups where \(k\) D3-branes get
dissolved in a probe D5-brane. Overlaps between Bethe eigenstates and these boundary states encode the one-point functions of conformal operators and are expressed in terms of the superdeterminant of the Gaudin matrix that in turn depends on the Dynkin diagram of the symmetry algebra. The different possible Dynkin diagrams of super Lie algebras are related via fermionic dualities and we determine how overlap formulae transform under these dualities. As an application we show
how to consistently move between overlap formulae obtained for \(k=1\) from different Dynkin diagrams. –––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
The \(\mathfrak{psu}(2,2|4)\) integrable super spin chain underlying the AdS/CFT correspondence has integrable boundary states which describe set-ups where \(k\) D3-branes get
dissolved in a probe D5-brane. Overlaps between Bethe eigenstates and these boundary states encode the one-point functions of conformal operators and are expressed in terms of the superdeterminant of the Gaudin matrix that in turn depends on the Dynkin diagram of the symmetry algebra. The different possible Dynkin diagrams of super Lie algebras are related via fermionic dualities and we determine how overlap formulae transform under these dualities. As an application we show
how to consistently move between overlap formulae obtained for \(k=1\) from different Dynkin diagrams. –––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: andrea
Wed
20 Jan 2021
Towards all loop supergravity amplitudes
๐ London
Agnese Bissi
(Uppsala University)
Abstract:
In this talk I will discuss how to extract the most trascendental piece of the four graviton amplitude in type IIB supergravity on AdS_5 \times S_5 at any loop order, from the dual four point function in N=4 Super Yang Mills. I will describe how to construct this part of the correlator/amplitude and its significance. I will conclude with some open problems and future directions.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
In this talk I will discuss how to extract the most trascendental piece of the four graviton amplitude in type IIB supergravity on AdS_5 \times S_5 at any loop order, from the dual four point function in N=4 Super Yang Mills. I will describe how to construct this part of the correlator/amplitude and its significance. I will conclude with some open problems and future directions.
[Please email alejandro.cabo_bizet@kcl.ac.uk for the Zoom link]
Posted by: andrea
Wed
20 Jan 2021
AdS Euclidean wormholes
Jorge Santos
(Cambridge)
Abstract:
``We explore the construction and stability of asymptotically anti-de Sitter Euclidean wormholes in a variety of models. In simple ad hoc low-energy models, it is not hard to construct two-boundary Euclidean wormholes that dominate over disconnected solutions and which are stable (lacking negative modes) in the usual sense of Euclidean quantum gravity. Indeed, the structure of such solutions turns out to strongly resemble that of the Hawking-Page phase transition for AdS-Schwarzschild black holes, in that for boundary sources above some threshold we find both a `large' and a `small' branch of wormhole solutions with the latter being stable and dominating over the disconnected solution for large enough sources. We are also able to construct two-boundary Euclidean wormholes in a variety of string compactifications with a similar that dominate over the disconnected solutions we find and that are stable with respect to field-theoretic perturbations. However, as in classic examples investigated by Maldacena and Maoz, the wormholes in these UV-complete settings always suffer from brane-nucleation instabilities (even when sources that one might hope would stabilize such instabilities are tuned to large values). This indicates the existence of additional disconnected solutions with lower action. We discuss the significance of such results for the factorization problem of AdS/CFT.รขโฌโข'
Join Zoom Meeting
https://zoom.us/j/98062076339?pwd=aGJNUTBTNjBYeDhqUlZVMzdVWkhGQT09
Meeting ID: 980 6207 6339
Passcode: 913115
``We explore the construction and stability of asymptotically anti-de Sitter Euclidean wormholes in a variety of models. In simple ad hoc low-energy models, it is not hard to construct two-boundary Euclidean wormholes that dominate over disconnected solutions and which are stable (lacking negative modes) in the usual sense of Euclidean quantum gravity. Indeed, the structure of such solutions turns out to strongly resemble that of the Hawking-Page phase transition for AdS-Schwarzschild black holes, in that for boundary sources above some threshold we find both a `large' and a `small' branch of wormhole solutions with the latter being stable and dominating over the disconnected solution for large enough sources. We are also able to construct two-boundary Euclidean wormholes in a variety of string compactifications with a similar that dominate over the disconnected solutions we find and that are stable with respect to field-theoretic perturbations. However, as in classic examples investigated by Maldacena and Maoz, the wormholes in these UV-complete settings always suffer from brane-nucleation instabilities (even when sources that one might hope would stabilize such instabilities are tuned to large values). This indicates the existence of additional disconnected solutions with lower action. We discuss the significance of such results for the factorization problem of AdS/CFT.รขโฌโข'
Join Zoom Meeting
https://zoom.us/j/98062076339?pwd=aGJNUTBTNjBYeDhqUlZVMzdVWkhGQT09
Meeting ID: 980 6207 6339
Passcode: 913115
Posted by: IC
Tue
19 Jan 2021
Extensions to GR: Roadblocks and potential way through
Luis Lehner
(Perimeter Institute for Theoretical Physics)
Abstract:
The search for extensions to GR, has prompted the developments of many potential options which, to varying degrees, have been studied and confronted with observations in special regimes –typically linear ones with respect to rather 'simple' scenarios. Gravitational wave astronomy provides the opportunity to confront them in a much richer and complex regime which unearths significant roadblocks that obstruct the definition and/or study of consequences of many of such extensions. This talk will review some of these problems, illustrate consequences and discuss a potential way through for studying the potential role such extensions might have in the strongly gravitating/non-linear regime.
[please email a.held@imperial.ac.uk for zoom link or password]
The search for extensions to GR, has prompted the developments of many potential options which, to varying degrees, have been studied and confronted with observations in special regimes –typically linear ones with respect to rather 'simple' scenarios. Gravitational wave astronomy provides the opportunity to confront them in a much richer and complex regime which unearths significant roadblocks that obstruct the definition and/or study of consequences of many of such extensions. This talk will review some of these problems, illustrate consequences and discuss a potential way through for studying the potential role such extensions might have in the strongly gravitating/non-linear regime.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC
Thu
14 Jan 2021
Integrability and Braided Tensor Categories
Paul Fendley
(Oxford)
Abstract:
Many integrable critical classical statistical mechanical models and the corresponding quantum spin chains possess a fractional-spin conserved current. These currents have been constructed by utilising quantum-group algebras, fermionic and parafermionic operators, and ideas from ``discrete holomorphicity''. I define them generally and naturally using a braided tensor category, a topological structure familiar from the study of knot invariants, anyons and conformal field theory. Such a current amounts to terminating a lattice topological defect, and I will touch on related work on such done with Aasen and Mong. I show how requiring a current be conserved yields simple constraints on the Boltzmann weights, and that all of the many models known to satisfy these constraints are integrable. This procedure therefore gives a linear construction for ``Baxterising'', i.e. building a solution of the Yang-Baxter equation out of topological data.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Many integrable critical classical statistical mechanical models and the corresponding quantum spin chains possess a fractional-spin conserved current. These currents have been constructed by utilising quantum-group algebras, fermionic and parafermionic operators, and ideas from ``discrete holomorphicity''. I define them generally and naturally using a braided tensor category, a topological structure familiar from the study of knot invariants, anyons and conformal field theory. Such a current amounts to terminating a lattice topological defect, and I will touch on related work on such done with Aasen and Mong. I show how requiring a current be conserved yields simple constraints on the Boltzmann weights, and that all of the many models known to satisfy these constraints are integrable. This procedure therefore gives a linear construction for ``Baxterising'', i.e. building a solution of the Yang-Baxter equation out of topological data.
–––––––––– Part of the London Integrability Journal Club. New participants please register using the form at integrability-london.weebly.com.
Posted by: andrea
Tue
12 Jan 2021
Probing the scale of grand unification with gravitational waves
Valerie Domcke
(CERN and EPFL, Lausanne)
Abstract:
Cosmic strings arise as remnants of phase transitions in the early Universe, often related to theories of grand unification (GUTs). If such a phase transitions occurs at high energies, the resulting cosmic string network generates a sizable amount of gravitational waves. Most work so far has focused on the gravitational wave signal from topologically stable cosmic strings. In this talk I will introduce metastable cosmic strings, which are a generic consequence of many GUTs. I will discuss how this idea can be probed in various ongoing and upcoming gravitational wave experiments, from pulsar timing arrays to space- and ground-based interferometers. In the final part of my talk I will discuss a recent proposal on using the radio telescopes to probe this and other sources of ultra high frequency gravitational waves.
[please email a.held@imperial.ac.uk for zoom link or password]
Cosmic strings arise as remnants of phase transitions in the early Universe, often related to theories of grand unification (GUTs). If such a phase transitions occurs at high energies, the resulting cosmic string network generates a sizable amount of gravitational waves. Most work so far has focused on the gravitational wave signal from topologically stable cosmic strings. In this talk I will introduce metastable cosmic strings, which are a generic consequence of many GUTs. I will discuss how this idea can be probed in various ongoing and upcoming gravitational wave experiments, from pulsar timing arrays to space- and ground-based interferometers. In the final part of my talk I will discuss a recent proposal on using the radio telescopes to probe this and other sources of ultra high frequency gravitational waves.
[please email a.held@imperial.ac.uk for zoom link or password]
Posted by: IC