Triangle Seminars
August 2016
Mon
29 Aug 2016
STiL 2016: Supersymmetry, Geometry, and Holography
📍 London
- -
(-)
Abstract:
29 August - 3 September, King's College London. <br><br>
This workshop intends to bring together leading experts and young researchers working on the broad themes of quantum field theory, black holes and gravitation, and holography, so as to share new ideas, calculations, and results in a focused setting. <br><br>
The topics covered in the workshop include:
<ul>
<li> Symmetries and dualities in field theory and gravity </li>
<li> Classical and quantum aspects of black holes </li>
<li> Supersymmetric localization and exact results </li>
<li> Mathematical aspects of string theory </li>
<li> Supergravity solutions and holography </li>
</ul>
<a href="https://dl.dropboxusercontent.com/u/45637246/STIL2016/home.html" target="_blank">Website</a>
<br><br>
Registration will be closed on 8 July 2016 or when positions are filled.
29 August - 3 September, King's College London. <br><br>
This workshop intends to bring together leading experts and young researchers working on the broad themes of quantum field theory, black holes and gravitation, and holography, so as to share new ideas, calculations, and results in a focused setting. <br><br>
The topics covered in the workshop include:
<ul>
<li> Symmetries and dualities in field theory and gravity </li>
<li> Classical and quantum aspects of black holes </li>
<li> Supersymmetric localization and exact results </li>
<li> Mathematical aspects of string theory </li>
<li> Supergravity solutions and holography </li>
</ul>
<a href="https://dl.dropboxusercontent.com/u/45637246/STIL2016/home.html" target="_blank">Website</a>
<br><br>
Registration will be closed on 8 July 2016 or when positions are filled.
Posted by: KCL
Wed
3 Aug 2016
(2,2) Abelian GLSM string vacua and mirror symmetry
Ronen Plesser
(Duke)
Abstract:
Mirror symmetry of Calabi—Yau spaces is best understood for families presented as complete intersections in toric varieties; these models have a description as the low-energy
limit of Abelian gauged linear sigma models (GLSMs). We investigate the combinatorial conditions on GLSM data such that the generic member of the family determines a non-singular low energy theory. A sufficient condition is reflexivity; this has the pleasant feature that the mirror
of a reflexive model is reflexive. This condition is certainly not necessary, in particular it is not preserved by extremal transitions. We propose a weaker condition that is preserved, but is also too strong. Along the way we describe how the Berglund—Hubsch mirror construction is related to the Batyrev—Boris combinatorial duality related to Abelian duality. We study the locus in parameter
space along which the model becomes singular and the invariance of this under mirror symmetry, finding support for the observation of Hori and Vafa that mirror symmetry is most naturally stated in terms of local Calabi—Yau models.
Mirror symmetry of Calabi—Yau spaces is best understood for families presented as complete intersections in toric varieties; these models have a description as the low-energy
limit of Abelian gauged linear sigma models (GLSMs). We investigate the combinatorial conditions on GLSM data such that the generic member of the family determines a non-singular low energy theory. A sufficient condition is reflexivity; this has the pleasant feature that the mirror
of a reflexive model is reflexive. This condition is certainly not necessary, in particular it is not preserved by extremal transitions. We propose a weaker condition that is preserved, but is also too strong. Along the way we describe how the Berglund—Hubsch mirror construction is related to the Batyrev—Boris combinatorial duality related to Abelian duality. We study the locus in parameter
space along which the model becomes singular and the invariance of this under mirror symmetry, finding support for the observation of Hori and Vafa that mirror symmetry is most naturally stated in terms of local Calabi—Yau models.
Posted by: IC
July 2016
Tue
19 Jul 2016
Super String Field Theory Revisited
Ivo Sachs
(LMU)
Abstract:
I first describe the remarkably simple algebraic structure underlying covariant string field theory. No knowledge of string field theory and only very basic concepts of string theory are required for this. I then use this structure to construct the superstring field theory action recursively and discuss its relation to the decomposition of (super) moduli spaces. I will focus mostly on open string theory but will comment on the generalisation to closed string.
I first describe the remarkably simple algebraic structure underlying covariant string field theory. No knowledge of string field theory and only very basic concepts of string theory are required for this. I then use this structure to construct the superstring field theory action recursively and discuss its relation to the decomposition of (super) moduli spaces. I will focus mostly on open string theory but will comment on the generalisation to closed string.
Posted by: IC
June 2016
Thu
23 Jun 2016
Bremsstrahlung function, leading Luscher correction at weak coupling and localization
Michelangelo Preti
(Parma U.)
Abstract:
We discuss the near BPS expansion of the generalized cusp anomalous dimension with L units of R-charge. Integrability provides an exact solution, obtained by solving a general TBA equation in the appropriate limit: we propose here an alternative method based on supersymmetric localization. The basic idea is to relate the computation to the vacuum expectation value of certain 1/8 BPS Wilson loops with local operator insertions along the contour. These observables localize on a two-dimensional gauge theory on S^2, opening the possibility of exact calculations. As a test of our proposal, we reproduce the leading Luscher correction at weak coupling to the generalized cusp anomalous dimension. This result is also checked against a genuine Feynman diagram approach in N=4 Super Yang-Mills theory.
We discuss the near BPS expansion of the generalized cusp anomalous dimension with L units of R-charge. Integrability provides an exact solution, obtained by solving a general TBA equation in the appropriate limit: we propose here an alternative method based on supersymmetric localization. The basic idea is to relate the computation to the vacuum expectation value of certain 1/8 BPS Wilson loops with local operator insertions along the contour. These observables localize on a two-dimensional gauge theory on S^2, opening the possibility of exact calculations. As a test of our proposal, we reproduce the leading Luscher correction at weak coupling to the generalized cusp anomalous dimension. This result is also checked against a genuine Feynman diagram approach in N=4 Super Yang-Mills theory.
Posted by: QMW
Thu
16 Jun 2016
Surface defects as vortex strings in class S_k
Hironori Mori
(Osaka University)
Abstract:
We investigate the aspects of surface defects in a new class of 4d N=1 superconformal quiver theories named class S_k. As the first step, we focus on the construction of the surface defects in IR under the situation where the UV theories of class S_k are higgsed by giving the vevs to some fields and try to specify them as 2d N=(0,2) vortex string theories by computing its elliptic genera encoded in the IR description of the superconformal indices of class S_k. This picture is consistent with type IIA brane construction of the vortex strings. Another way to argue the surface defects is to see their actions on the superconformal indices as difference operators, and we would like to discuss whether such difference operators form the algebras labelled by the representations of SU(N) flavor symmetries.
We investigate the aspects of surface defects in a new class of 4d N=1 superconformal quiver theories named class S_k. As the first step, we focus on the construction of the surface defects in IR under the situation where the UV theories of class S_k are higgsed by giving the vevs to some fields and try to specify them as 2d N=(0,2) vortex string theories by computing its elliptic genera encoded in the IR description of the superconformal indices of class S_k. This picture is consistent with type IIA brane construction of the vortex strings. Another way to argue the surface defects is to see their actions on the superconformal indices as difference operators, and we would like to discuss whether such difference operators form the algebras labelled by the representations of SU(N) flavor symmetries.
Posted by: QMW
Wed
15 Jun 2016
Extending the scope of holographic mutual information and chaotic behavior
Nilanjan Sircar
(Tel Aviv)
Abstract:
We extend the use of holography to investigate the "Scrambling" (a.k.a "Chaos", "Butterfly Effect", "Thermalization") properties of various physical systems at finite temperature. Specifically, we consider: (i) non-conformal backgrounds of black Dp branes, (ii) asymptotically Lifshitz black holes, and (iii) black AdS solutions of Gauss-Bonnet gravity.
We use the disruption of the mutual information as a probe of the chaotic feature of such systems. Our analysis shows that these theories share the same type of behavior as conformal theories as they undergo chaos, however, in the case of Gauss-Bonnet gravity, we find a stark difference in the evolution of the mutual information for negative Gauss-Bonnet coupling. This may signal an inconsistency of the latter.
We extend the use of holography to investigate the "Scrambling" (a.k.a "Chaos", "Butterfly Effect", "Thermalization") properties of various physical systems at finite temperature. Specifically, we consider: (i) non-conformal backgrounds of black Dp branes, (ii) asymptotically Lifshitz black holes, and (iii) black AdS solutions of Gauss-Bonnet gravity.
We use the disruption of the mutual information as a probe of the chaotic feature of such systems. Our analysis shows that these theories share the same type of behavior as conformal theories as they undergo chaos, however, in the case of Gauss-Bonnet gravity, we find a stark difference in the evolution of the mutual information for negative Gauss-Bonnet coupling. This may signal an inconsistency of the latter.
Posted by: IC
Thu
2 Jun 2016
Supertanslation symmetry at the black hole horizon
Gaston Giribet
(University of Buenos Aires)
Wed
1 Jun 2016
Non-abelian particle-vortex duality
Jeff Murugan
(University of Cape Town)
Abstract:
Quantum field theories in (2+1)-dimensions exhibit a beautiful property known as particle-vortex duality. It relates, in a precise way, two different excitations on the plane, the familiar particle-like excitations that arise from quantisation of the field and vortices, solitonic-excitations defined by the winding of a local order parameter. Originally studied in the context of anyonic superconductivity and Neilsen-Olesen vortices, extensions of the duality have recently found application to, for example, topological quantum matter. I will review some of these developments and show how recent progress in understanding non-abelian T-duality can be used to define a non-abelian particle-vortex duality in (2+1)-dimensions.
Quantum field theories in (2+1)-dimensions exhibit a beautiful property known as particle-vortex duality. It relates, in a precise way, two different excitations on the plane, the familiar particle-like excitations that arise from quantisation of the field and vortices, solitonic-excitations defined by the winding of a local order parameter. Originally studied in the context of anyonic superconductivity and Neilsen-Olesen vortices, extensions of the duality have recently found application to, for example, topological quantum matter. I will review some of these developments and show how recent progress in understanding non-abelian T-duality can be used to define a non-abelian particle-vortex duality in (2+1)-dimensions.
Posted by: IC
May 2016
Thu
26 May 2016
Super String Field Theory Revisited
Ivo Sachs
(LMU)
Abstract:
I first describe the remarkably simple algebraic structure underlying
covariant string field theory. No knowledge of string field theory and
only very basic concepts of string theory are required for this. I
then use this structure to construct the superstring field theory
action recursively and discuss its relation to the decomposition of
(super) moduli spaces. I will focus mostly on open string theory but
will comment on the generalisation to closed string.
I first describe the remarkably simple algebraic structure underlying
covariant string field theory. No knowledge of string field theory and
only very basic concepts of string theory are required for this. I
then use this structure to construct the superstring field theory
action recursively and discuss its relation to the decomposition of
(super) moduli spaces. I will focus mostly on open string theory but
will comment on the generalisation to closed string.
Posted by: QMW
Fri
20 May 2016
Graduate Mini-Course: Sectors of Supersymmetric Field Theories
Matthew Buican
(QMUL)
Abstract:
Lecture 3: "Toward a Synthesis of Chiral Rings and Chiral Algebras."
I will aim to discuss some recent work that seeks to relate the objects introduced in the first two lectures. Given enough time, we may also discuss generalizations of these ideas.
Lecture 3: "Toward a Synthesis of Chiral Rings and Chiral Algebras."
I will aim to discuss some recent work that seeks to relate the objects introduced in the first two lectures. Given enough time, we may also discuss generalizations of these ideas.
Posted by: QMW
Thu
19 May 2016
d-Dimensional Generalised Unitarity and Colour-Kinematics duality
William Javier Torres Bobadilla
(Padua U.)
Abstract:
In this talk I plan to introduce the Four-Dimensional-Formulation (FDF) regularisation scheme
proposed in arXiv:1404.4783 [hep-ph], which allows a four-dimensional representation of the d-dimensional particles propagating in the loop. Within FDF, I present the computation of one-loop QCD corrections of the processes gg>>gggg and gg>>Hggg (in the heavy top limit).
On the other hand, I show the extension of Colour-Kinematics relations in d-dimensions and their application to compute efficiently one-loop amplitudes.
In this talk I plan to introduce the Four-Dimensional-Formulation (FDF) regularisation scheme
proposed in arXiv:1404.4783 [hep-ph], which allows a four-dimensional representation of the d-dimensional particles propagating in the loop. Within FDF, I present the computation of one-loop QCD corrections of the processes gg>>gggg and gg>>Hggg (in the heavy top limit).
On the other hand, I show the extension of Colour-Kinematics relations in d-dimensions and their application to compute efficiently one-loop amplitudes.
Posted by: QMW
Wed
18 May 2016
Graduate Mini-Course: Sectors of Supersymmetric Field Theories
Matthew Buican
(QMUL)
Abstract:
Lecture 2: "Chiral Algebras and Higher-Dimensional Theories."
I will review briefly review the construction of chiral algebras and then focus on their relationship with a particular sub-sector of operators in higher-dimensional theories. I will again focus mostly on 4D N=2 theories.
Lecture 2: "Chiral Algebras and Higher-Dimensional Theories."
I will review briefly review the construction of chiral algebras and then focus on their relationship with a particular sub-sector of operators in higher-dimensional theories. I will again focus mostly on 4D N=2 theories.
Posted by: QMW
Mon
16 May 2016
Graduate Mini-Course: Sectors of Supersymmetric Field Theories
Matthew Buican
(QMUL)
Abstract:
Lecture 1: "Chiral Rings, Moduli Spaces, and Conformal Manifolds."
In this lecture I will review basic aspects of chiral operators, with a special focus on 4D theories with 8 Poincare supercharges (i.e., N=2 SUSY). Using these operators, I will discuss basic aspects of moduli spaces and conformal manifolds.
Lecture 1: "Chiral Rings, Moduli Spaces, and Conformal Manifolds."
In this lecture I will review basic aspects of chiral operators, with a special focus on 4D theories with 8 Poincare supercharges (i.e., N=2 SUSY). Using these operators, I will discuss basic aspects of moduli spaces and conformal manifolds.
Posted by: QMW
Thu
12 May 2016
One-point Functions of AdS/dCFT from Matrix Product States
Charlotte Kristjansen
(NBI)
Abstract:
One-point functions of certain non-protected scalar operators in the defect CFT dual to the D3-D5 probe brane system with k units of world volume flux can be expressed as overlaps between Bethe eigenstates of the Heisenberg spin chain and a matrix product state. We present a closed expression of determinant form for these one-point functions, valid for any value of k. The determinant formula factorizes into the k=2 result times a k-dependent prefactor. Making use of the transfer matrix of the Heisenberg spin chain we recursively relate the matrix product state for higher even and odd k to the matrix product state for k=2 and k=3 respectively. We furthermore find evidence that the matrix product states for k=2 and k=3 are related via a ratio of Baxter's Q-operators. The general k formula has an interesting thermodynamical limit involving a non-trivial scaling of k, which indicates that the match between string and field theory one-point functions found for chiral primaries might be tested for non-protected operators as well. We revisit the string computation for chiral primaries and discuss how it can be extended to non-protected operators.
One-point functions of certain non-protected scalar operators in the defect CFT dual to the D3-D5 probe brane system with k units of world volume flux can be expressed as overlaps between Bethe eigenstates of the Heisenberg spin chain and a matrix product state. We present a closed expression of determinant form for these one-point functions, valid for any value of k. The determinant formula factorizes into the k=2 result times a k-dependent prefactor. Making use of the transfer matrix of the Heisenberg spin chain we recursively relate the matrix product state for higher even and odd k to the matrix product state for k=2 and k=3 respectively. We furthermore find evidence that the matrix product states for k=2 and k=3 are related via a ratio of Baxter's Q-operators. The general k formula has an interesting thermodynamical limit involving a non-trivial scaling of k, which indicates that the match between string and field theory one-point functions found for chiral primaries might be tested for non-protected operators as well. We revisit the string computation for chiral primaries and discuss how it can be extended to non-protected operators.
Posted by: QMW
Wed
11 May 2016
Semiholographic QFTs and applications
Ayan Mukhopadhyay
(TU Wien)
Abstract:
I will argue that a semiholographic framework can lead us to unravel general aspects of many quantum many body systems with strongly interacting degrees of freedom. I will present the case for QCD and some other QFTs. In particular, applications to heavy ion physics and hadronic physics will be discussed. A derivation of the framework combining exact Wilsonian RG and holographic RG will be sketched.
I will argue that a semiholographic framework can lead us to unravel general aspects of many quantum many body systems with strongly interacting degrees of freedom. I will present the case for QCD and some other QFTs. In particular, applications to heavy ion physics and hadronic physics will be discussed. A derivation of the framework combining exact Wilsonian RG and holographic RG will be sketched.
Posted by: IC
Thu
5 May 2016
Quantum Linguistics?
Mehrnoosh Sadrzadeh
(QMUL)
Abstract:
Mathematical models of natural language can be organised into logical and
statistical. The former are based on grammatical structures of
phrases and sentences and the latter on distributions of words in corpora
of text. In joint work with Clark (Cambridge) and Coecke (Oxford), we developed a unifying
framework where the distributions of words are composed to form
distributions for phrases and sentences. This expanded the application
domains of the statistical models – e.g. automatic reasoning about
similarity – from words to phrases and sentences.
On the theoretical side, our model extends the word-based setting from vectors to tensors.
Tensors are main players in the mathematical models of quantum mechanics.
In this talk, I will review the theory and applications of our
model in simple terms and through examples. I will briefly explain how
`entanglement', a concept arising from tensors in quantum mechanics,
manifests itself and is used as a resource in the linguistic applications.
I will also explain how the reasoning toolkit used in this model is the same as that of Abramsky and Coecke in their
categorical Quantum Mechanics model.
Mathematical models of natural language can be organised into logical and
statistical. The former are based on grammatical structures of
phrases and sentences and the latter on distributions of words in corpora
of text. In joint work with Clark (Cambridge) and Coecke (Oxford), we developed a unifying
framework where the distributions of words are composed to form
distributions for phrases and sentences. This expanded the application
domains of the statistical models – e.g. automatic reasoning about
similarity – from words to phrases and sentences.
On the theoretical side, our model extends the word-based setting from vectors to tensors.
Tensors are main players in the mathematical models of quantum mechanics.
In this talk, I will review the theory and applications of our
model in simple terms and through examples. I will briefly explain how
`entanglement', a concept arising from tensors in quantum mechanics,
manifests itself and is used as a resource in the linguistic applications.
I will also explain how the reasoning toolkit used in this model is the same as that of Abramsky and Coecke in their
categorical Quantum Mechanics model.
Posted by: QMW
April 2016
Thu
28 Apr 2016
Black Hole Collisions in Asymptotically anti-de Sitter Spacetimes
Hans Bantilan
(QMUL)
Abstract:
The collision of black holes is a classic problem in the strong-field regime of general relativity, with no known closed-form solution. When exact solutions are not known, or perturbative expansions about known solutions are inadequate to capture the non-linear dynamics, the numerical solution of the Einstein field equations is required. The main purpose of this talk is to describe, in detail, the necessary ingredients for achieving stable Cauchy evolution of black hole collisions in asymptotically anti-de Sitter (AdS) spacetimes. I will begin by motivating this program in terms of the heavy-ion physics it is intended to clarify. I will then give an overview of anti-de Sitter space, the mapping to its dual boundary conformal field theory, and the method we use to numerically solve the fully non-linear Einstein field equations with AdS boundary conditions. As a concrete example of these ideas, I will describe simulations of stable AdS black hole mergers in 5 dimensions.
The collision of black holes is a classic problem in the strong-field regime of general relativity, with no known closed-form solution. When exact solutions are not known, or perturbative expansions about known solutions are inadequate to capture the non-linear dynamics, the numerical solution of the Einstein field equations is required. The main purpose of this talk is to describe, in detail, the necessary ingredients for achieving stable Cauchy evolution of black hole collisions in asymptotically anti-de Sitter (AdS) spacetimes. I will begin by motivating this program in terms of the heavy-ion physics it is intended to clarify. I will then give an overview of anti-de Sitter space, the mapping to its dual boundary conformal field theory, and the method we use to numerically solve the fully non-linear Einstein field equations with AdS boundary conditions. As a concrete example of these ideas, I will describe simulations of stable AdS black hole mergers in 5 dimensions.
Posted by: QMW
Thu
28 Apr 2016
Towards a theory of gravitational radiation
📍 London
Pawel Nurowski
(Centre for Theoretical Physics, Polish Academy of Sciences, Warsaw, Poland)
Abstract:
The recent observation of gravitational waves by LIGO has revived interest in the work on the theory of gravitational radiation done at King's and elsewhere in the 1950's and early 60's. It is well known that after predicting gravitational waves in 1916 Einstein became uncertain about their physical reality. It wasn't until the 1950's and early 60's that their physical status was clarified. Important contributions to the development of the theory of gravitational radiation were made at this time by members of the King's relativity group such as Hermann Bondi, Felix Pirani and Roger Penrose. In 1958 Andrzej Trautman from Leopold Infeld's relativity group in Warsaw delivered a series of highly influential lectures on gravitational radiation at King's. In this talk the work of the Warsaw group, and Trautman in particular, will be discussed and its influence on the development of gravitational wave
theory will be explained.
Refreshments will be available after the lecture. Please RSVP to:
D C Robinson
david.c.robinson@kcl.ac.uk
The recent observation of gravitational waves by LIGO has revived interest in the work on the theory of gravitational radiation done at King's and elsewhere in the 1950's and early 60's. It is well known that after predicting gravitational waves in 1916 Einstein became uncertain about their physical reality. It wasn't until the 1950's and early 60's that their physical status was clarified. Important contributions to the development of the theory of gravitational radiation were made at this time by members of the King's relativity group such as Hermann Bondi, Felix Pirani and Roger Penrose. In 1958 Andrzej Trautman from Leopold Infeld's relativity group in Warsaw delivered a series of highly influential lectures on gravitational radiation at King's. In this talk the work of the Warsaw group, and Trautman in particular, will be discussed and its influence on the development of gravitational wave
theory will be explained.
Refreshments will be available after the lecture. Please RSVP to:
D C Robinson
david.c.robinson@kcl.ac.uk
Posted by: KCL
Thu
21 Apr 2016
Tachyonic Antibranes and the deSitter and Fuzzball Landscapes
Iosif Bena
(Saclay)
Abstract:
Antibranes in backgrounds that have charge dissolved in fluxes are a key ingredient in constructing a landscape (Multiverse) of deSitter vacua in String Theory, and also of constructing microstate solutions corresponding to non-supersymmetric near-extremal black holes. There are several regimes of parameters in which one can study the physics of these antibranes, and I will show that in the regime of parameters where their gravitational backreaction is important, antibranes have a naked singularity that cannot be resolved either by brane polarization or by cloaking with a black hole horizon, and that signals a tachyonic instability. I will also present recent evidence that the theory on the wordvolume of anti-D3 branes is finite to all loops. I will conclude by discussing the implications of these results for the Multiverse paradigm and for the Fuzzball proposal.
Antibranes in backgrounds that have charge dissolved in fluxes are a key ingredient in constructing a landscape (Multiverse) of deSitter vacua in String Theory, and also of constructing microstate solutions corresponding to non-supersymmetric near-extremal black holes. There are several regimes of parameters in which one can study the physics of these antibranes, and I will show that in the regime of parameters where their gravitational backreaction is important, antibranes have a naked singularity that cannot be resolved either by brane polarization or by cloaking with a black hole horizon, and that signals a tachyonic instability. I will also present recent evidence that the theory on the wordvolume of anti-D3 branes is finite to all loops. I will conclude by discussing the implications of these results for the Multiverse paradigm and for the Fuzzball proposal.
Posted by: QMW
Thu
14 Apr 2016
Constraints on the CFT three point functions
Manuela Kulaxizi
(Trinity College Dublen)
Abstract:
We discuss the energy flux constraints for conserved and non-conserved operators in an arbitrary higher dimensional CFT. We then consider a deep inelastic scattering thought experiment and show how to derive these and other bounds on the OPE coefficients of various operators.
We discuss the energy flux constraints for conserved and non-conserved operators in an arbitrary higher dimensional CFT. We then consider a deep inelastic scattering thought experiment and show how to derive these and other bounds on the OPE coefficients of various operators.
Posted by: QMW
Thu
7 Apr 2016
Scrambling without chaos
Alvaro Veliz Osorio
(QMUL)
Abstract:
We investigate measures of chaos and entanglement scrambling in rational conformal field theories in 1+1 dimensions. First, we derive a formula for the late time value of the out-of-time-order correlators for these class of theories. Our universal result can be expressed as a particular combination of the modular S-matrix elements known as anyon monodromy scalar. Next, in the explicit setup of a SU(N)k WZW model, we compare the late time behaviour of the out-of-time correlators and the purity. Interestingly, in the large-c limit, the purity grows logarithmically but the out-of-time-order correlators remain constant. Therefore, we find that some systems may display entanglement scrambling in the absence of chaos.
We investigate measures of chaos and entanglement scrambling in rational conformal field theories in 1+1 dimensions. First, we derive a formula for the late time value of the out-of-time-order correlators for these class of theories. Our universal result can be expressed as a particular combination of the modular S-matrix elements known as anyon monodromy scalar. Next, in the explicit setup of a SU(N)k WZW model, we compare the late time behaviour of the out-of-time correlators and the purity. Interestingly, in the large-c limit, the purity grows logarithmically but the out-of-time-order correlators remain constant. Therefore, we find that some systems may display entanglement scrambling in the absence of chaos.
Posted by: QMW
March 2016
Thu
31 Mar 2016
Bootstrapping N=2 SCFTs
Madalena Lemos
(DESY Hamburg)
Abstract:
In this talk we will discuss the bootstrap program applied to four-dimensional N=2 superconformal field theories, with focus on analytical results. After a brief review of the protected subsector captured by a two-dimensional chiral algebra, we will show how analytic bounds on anomaly coefficients are obtained and constrain the space of allowed SCFTs. Finally we will comment the implications for the numerical bootstrap program.
In this talk we will discuss the bootstrap program applied to four-dimensional N=2 superconformal field theories, with focus on analytical results. After a brief review of the protected subsector captured by a two-dimensional chiral algebra, we will show how analytic bounds on anomaly coefficients are obtained and constrain the space of allowed SCFTs. Finally we will comment the implications for the numerical bootstrap program.
Posted by: QMW
Wed
30 Mar 2016
On Killing superalgebras and filtered deformations
📍 London
Andrea Santi
(University of Edinburgh, Marie-Curie INdAM)
Abstract:
I will present ongoing work with J. Figueroa-O’Farrill and P. de Medeiros
on the algebraic structure of Lie superalgebras \(g = g_0 \oplus g_1\) generated by Killing spinors. I will explain how any \(g\) can be regarded as an appropriate
deformation of a subalgebra of the Poincaré superalgebra and discuss applications to the classification of supersymmetric supergravity backgrounds
and the geometries admitting rigidly supersymmetric field theories.
I will present ongoing work with J. Figueroa-O’Farrill and P. de Medeiros
on the algebraic structure of Lie superalgebras \(g = g_0 \oplus g_1\) generated by Killing spinors. I will explain how any \(g\) can be regarded as an appropriate
deformation of a subalgebra of the Poincaré superalgebra and discuss applications to the classification of supersymmetric supergravity backgrounds
and the geometries admitting rigidly supersymmetric field theories.
Posted by: KCL
Wed
23 Mar 2016
Opers and the E6 Minahan-Nemeschansky theory
📍 London
Lotte Hollands
(Heriot-Watt U., Edinburgh)
Abstract:
In this seminar I explain a geometric proposal to determine a nonperturbative partition function for the E6 Minahan-Nemeschansky theory. Important ingredients are generating functions of opers, spectral networks and a generalisation of complex Fenchel-Nielsen coordinates to moduli spaces of higher rank flat connections. (This is joint work with Andy Neitzke.)
In this seminar I explain a geometric proposal to determine a nonperturbative partition function for the E6 Minahan-Nemeschansky theory. Important ingredients are generating functions of opers, spectral networks and a generalisation of complex Fenchel-Nielsen coordinates to moduli spaces of higher rank flat connections. (This is joint work with Andy Neitzke.)
Posted by: KCL
Thu
17 Mar 2016
Constraints from unitarity in Conformal Field Theories
Andrei Parnachev
(Trinity College Dublin)
Abstract:
We discuss implications of unitarity in CFTs and derive
a number of constraints, including positivity of energy flux constraint.
We discuss implications of unitarity in CFTs and derive
a number of constraints, including positivity of energy flux constraint.
Posted by: IC
Wed
16 Mar 2016
Prethermalization and thermalization in models with weak integrability breaking
📍 London
Fabian Essler
(Oxford U.)
Abstract:
I consider the the effect of weak integrability breaking
interactions on the non-equilibrium time evolution in many-particle systems. Using a class of weakly interaction fermion models as an example, I argue that there exists a time window in which the system relaxes locally to a non-equilibrium meta-stable state, before it eventually thermalizes.
I consider the the effect of weak integrability breaking
interactions on the non-equilibrium time evolution in many-particle systems. Using a class of weakly interaction fermion models as an example, I argue that there exists a time window in which the system relaxes locally to a non-equilibrium meta-stable state, before it eventually thermalizes.
Posted by: KCL
Wed
16 Mar 2016
AdS_5/CFT_4, N=3
📍 London
George Papadopoulos
(King's College London)
Abstract:
Polygon Seminar.
NOTE: Seminar is in the room G.73, Franklin-Wilkins, WATERLOO CAMPUS of King's College London.
http://www.kcl.ac.uk/campuslife/campuses/waterloo/Waterloo.aspx
Polygon Seminar.
NOTE: Seminar is in the room G.73, Franklin-Wilkins, WATERLOO CAMPUS of King's College London.
http://www.kcl.ac.uk/campuslife/campuses/waterloo/Waterloo.aspx
Posted by: KCL
Thu
10 Mar 2016
Six-dimensional field theories from string theory
Alessandro Tomasiello
(Milan)
Abstract:
I will review some recent progress about superconformal field theories in six dimensions. A simple class has an effective description in terms of a chain of gauge fields, coupled by tensors and hypermultiplets. Their holographic duals are now known analytically, and some precision checks can be performed, involving Weyl anomalies. An extension of this class can be studied using F-theory.
All these theories have some features in common with the elusive theory describing M5-branes, and indeed suggest new phenomena, such as M5 fractionation.
I will review some recent progress about superconformal field theories in six dimensions. A simple class has an effective description in terms of a chain of gauge fields, coupled by tensors and hypermultiplets. Their holographic duals are now known analytically, and some precision checks can be performed, involving Weyl anomalies. An extension of this class can be studied using F-theory.
All these theories have some features in common with the elusive theory describing M5-branes, and indeed suggest new phenomena, such as M5 fractionation.
Posted by: IC
Thu
10 Mar 2016
3d N=2 dualities with monopoles
Sara Pasquetti
(Surrey U.)
Abstract:
I will present several new 3d N=2 dualities with super-potentials involving monopole operators. Some of the theories that I will discuss describe systems of D3 branes ending on pq-webs. In these cases 3d mirror symmetry is a consequence of S-duality.
I will present several new 3d N=2 dualities with super-potentials involving monopole operators. Some of the theories that I will discuss describe systems of D3 branes ending on pq-webs. In these cases 3d mirror symmetry is a consequence of S-duality.
Posted by: QMW
Wed
9 Mar 2016
AdS Moduli Spaces and Domain Walls
📍 London
Hagen Triendl
(Imperial College)
Abstract:
I discuss general properties of supersymmetric Anti-de Sitter (AdS) backgrounds, in particular regarding their moduli spaces and domain walls. I argue that lower-dimensional gauged supergravity is a strong tool to understand supersymmetric AdS backgrounds, independent of the compactification manifold. I show how the moduli space can be determined and explain what this means for the dual conformal field theories. In the last part I comment on supersymmetric domain walls and their dual interpretation as supersymmetric RG- flows.
I discuss general properties of supersymmetric Anti-de Sitter (AdS) backgrounds, in particular regarding their moduli spaces and domain walls. I argue that lower-dimensional gauged supergravity is a strong tool to understand supersymmetric AdS backgrounds, independent of the compactification manifold. I show how the moduli space can be determined and explain what this means for the dual conformal field theories. In the last part I comment on supersymmetric domain walls and their dual interpretation as supersymmetric RG- flows.
Posted by: KCL
Wed
9 Mar 2016
Dirty black holes and transport in strange metals
Andrew Lucas
(Harvard)
Abstract:
I will discuss what we have learned in the past year about transport in strongly interacting metallic phases by studying the linear response of planar black holes with broken translational symmetry. Firstly, I will discuss how holography tells us that the conductivity of weakly disordered metals is described by the Drude formula, confirming a "prediction" of the many-body memory matrix approach. Secondly, I will discuss the derivation of non-perturbative conductivity bounds, invoking a new version of the holographic membrane paradigm. These bounds rule out disorder-driven phase transitions (which would generically exist in traditional condensed matter models) in the boundary theory under rather mild assumptions about the existence and nature of solutions to Einstein's equations. Connections between these black-hole inspired theories of transport and novel experiments in graphene will also be discussed.
I will discuss what we have learned in the past year about transport in strongly interacting metallic phases by studying the linear response of planar black holes with broken translational symmetry. Firstly, I will discuss how holography tells us that the conductivity of weakly disordered metals is described by the Drude formula, confirming a "prediction" of the many-body memory matrix approach. Secondly, I will discuss the derivation of non-perturbative conductivity bounds, invoking a new version of the holographic membrane paradigm. These bounds rule out disorder-driven phase transitions (which would generically exist in traditional condensed matter models) in the boundary theory under rather mild assumptions about the existence and nature of solutions to Einstein's equations. Connections between these black-hole inspired theories of transport and novel experiments in graphene will also be discussed.
Posted by: IC
Mon
7 Mar 2016
Superconformal theories from M5 branes
Simone Giacomelli
(ULB - Bruxelles)
Abstract:
In this talk I will discuss superconformal theories in four
dimensions obtained wrapping M5 branes on a Riemann surface. I will
first review N=2 class S theories introduced some years ago by Gaiotto
and then describe a generalization to the N=1 case. For this class of
theories it is possible to write down a spectral curve encoding the
properties of the chiral ring and I propose a method to determine from
the spectral curve the scaling dimension of chiral operators in the
SCFT. This proposal reduces to the correct prescription in the special
case of N=2 theories. I will provide several consistency checks and
apply this method to study some new superconformal theories.
In this talk I will discuss superconformal theories in four
dimensions obtained wrapping M5 branes on a Riemann surface. I will
first review N=2 class S theories introduced some years ago by Gaiotto
and then describe a generalization to the N=1 case. For this class of
theories it is possible to write down a spectral curve encoding the
properties of the chiral ring and I propose a method to determine from
the spectral curve the scaling dimension of chiral operators in the
SCFT. This proposal reduces to the correct prescription in the special
case of N=2 theories. I will provide several consistency checks and
apply this method to study some new superconformal theories.
Posted by: IC
Wed
2 Mar 2016
Probing N=2 SUSY gauge theories with surface operators
Joerg Teschner
(DESY)
Wed
2 Mar 2016
Soft Hair on Black Holes
Malcolm Perry
(DAMTP)
February 2016
Fri
26 Feb 2016
S-matrix and conformal bootstrap
📍 London
Joao Penedones
(EPFL)
Abstract:
We propose a new strategy to constraint (and perhaps determine) the mass spectrum and the scattering amplitudes of a Quantum Field Theory (QFT).
We consider QFT in hyperbolic space and study correlation functions of operators inserted at the conformal boundary. By construction, these observables transform like correlation functions of a lower dimensional Conformal Field Theory. We then apply conformal bootstrap techniques to find universal bounds on the mass spectrum and scattering amplitudes of the QFT. For 1+1 dimensional QFT, we recover the same bounds from a direct S-matrix bootstrap approach.
We propose a new strategy to constraint (and perhaps determine) the mass spectrum and the scattering amplitudes of a Quantum Field Theory (QFT).
We consider QFT in hyperbolic space and study correlation functions of operators inserted at the conformal boundary. By construction, these observables transform like correlation functions of a lower dimensional Conformal Field Theory. We then apply conformal bootstrap techniques to find universal bounds on the mass spectrum and scattering amplitudes of the QFT. For 1+1 dimensional QFT, we recover the same bounds from a direct S-matrix bootstrap approach.
Posted by: KCL
Wed
24 Feb 2016
Higher Spin Black Holes
📍 London
Alejandra Castro
(Amsterdam U.)
Abstract:
I'll overview recent progress on non-perturbative aspects of higher spin theories in three dimensions with emphasis on black holes. The two main results I will discuss are: 1) novel properties of extremal and BPS solutions, and 2) how to interpret a higher spin bh as a thermo-field state.
I'll overview recent progress on non-perturbative aspects of higher spin theories in three dimensions with emphasis on black holes. The two main results I will discuss are: 1) novel properties of extremal and BPS solutions, and 2) how to interpret a higher spin bh as a thermo-field state.
Posted by: KCL
Wed
24 Feb 2016
Non-perturbative effective action of N=4 SYM in the Coulomb branch
Massimo Bianchi
(Rome (Tor Vergata))
Abstract:
We derive the one-instanton effective action of N=4 super Yang-Mills theory in terms of the N=4 on-shell superfields. In the Coulomb branch, instantons correct both the MHV and next-to-next-MHV higher derivative terms D^4F^{2n+2} and F^{2n+4}. We confirm at the non-perturbative level the non-renormalization theorems for MHV F^{2n+2} terms that are expected to receive perturbative corrections only at n-loops. We compute also the one and two-loop corrections to the D^4F^4 term and show that its completion under SL(2,Z) duality is consistent with the one-instanton results.
We derive the one-instanton effective action of N=4 super Yang-Mills theory in terms of the N=4 on-shell superfields. In the Coulomb branch, instantons correct both the MHV and next-to-next-MHV higher derivative terms D^4F^{2n+2} and F^{2n+4}. We confirm at the non-perturbative level the non-renormalization theorems for MHV F^{2n+2} terms that are expected to receive perturbative corrections only at n-loops. We compute also the one and two-loop corrections to the D^4F^4 term and show that its completion under SL(2,Z) duality is consistent with the one-instanton results.
Posted by: IC
Thu
18 Feb 2016
Collabor8 - A Meeting for Early Career Researchers in Mathematical and Theoretical Physics
Various Various
(Various)
Abstract:
Collabor8 is a day-long meeting for early career researchers in mathematical and theoretical physics on Thursday 18th February 2016. The purpose of the meeting is to encourage collaboration between PhD students and postdocs from different institutions and research specialisms working in the UK.
The meeting will feature short presentations from selected speakers about ongoing research problems, in contrast to traditional longer seminars on completed work. These will form the basis of group discussions, where participants may share their expertise and suggest new approaches. The conference website provides a convenient social network to promote continuing interaction after the meeting.
We are delighted that Professor Luis Fernando Alday will be delivering a keynote lecture at the meeting. There is no conference fee, and funds are available to reimburse travel expenses.
Further information about the meeting, including the registration form, may be found on the website below. The deadline for registration is Thursday 4th February.
http://www.collabor8research.org
Collabor8 is a day-long meeting for early career researchers in mathematical and theoretical physics on Thursday 18th February 2016. The purpose of the meeting is to encourage collaboration between PhD students and postdocs from different institutions and research specialisms working in the UK.
The meeting will feature short presentations from selected speakers about ongoing research problems, in contrast to traditional longer seminars on completed work. These will form the basis of group discussions, where participants may share their expertise and suggest new approaches. The conference website provides a convenient social network to promote continuing interaction after the meeting.
We are delighted that Professor Luis Fernando Alday will be delivering a keynote lecture at the meeting. There is no conference fee, and funds are available to reimburse travel expenses.
Further information about the meeting, including the registration form, may be found on the website below. The deadline for registration is Thursday 4th February.
http://www.collabor8research.org
Posted by: QMW
Wed
17 Feb 2016
Topological quantum field theory: symmetries and defects
📍 London
Nils Carqueville
(Schroedinger Inst., Vienna)
Abstract:
A major paradigm of 20th-century science is to understand nature in the language of quantum field theory. Efforts to answer foundational questions about this language have led to successful and ongoing cross-fertilisation between theoretical physics and pure mathematics. In particular, Atiyah and Segal proposed an axiomisation of the path integral by beautifully linking geometry with algebra.
The talk starts with a lightening review of this functorial approach, and then quickly restricts to the case in which spacetime is two-dimensional and has no geometric structure: two-dimensional topological quantum field theory (TQFT). This seemingly simple situation is still surprisingly rich, and we will see how algebras, categories, and "higher" structures appear naturally; examples of such structures are ubiquitous in theoretical physics, string theory, and many areas of mathematics.
Once the stage is carefully set, we turn to the central notion of symmetry, which involves the action of groups on a TQFT. We will be led to interpret symmetries as special kinds of "defects" of the TQFT, which in turn allows for a natural, purely algebraic generalisation of orbifolding. This leads to new equivalences between TQFTs, of which we will discuss the examples of Landau-Ginzburg models, and (if time permits) refined knot invariants.
A major paradigm of 20th-century science is to understand nature in the language of quantum field theory. Efforts to answer foundational questions about this language have led to successful and ongoing cross-fertilisation between theoretical physics and pure mathematics. In particular, Atiyah and Segal proposed an axiomisation of the path integral by beautifully linking geometry with algebra.
The talk starts with a lightening review of this functorial approach, and then quickly restricts to the case in which spacetime is two-dimensional and has no geometric structure: two-dimensional topological quantum field theory (TQFT). This seemingly simple situation is still surprisingly rich, and we will see how algebras, categories, and "higher" structures appear naturally; examples of such structures are ubiquitous in theoretical physics, string theory, and many areas of mathematics.
Once the stage is carefully set, we turn to the central notion of symmetry, which involves the action of groups on a TQFT. We will be led to interpret symmetries as special kinds of "defects" of the TQFT, which in turn allows for a natural, purely algebraic generalisation of orbifolding. This leads to new equivalences between TQFTs, of which we will discuss the examples of Landau-Ginzburg models, and (if time permits) refined knot invariants.
Posted by: KCL
Wed
17 Feb 2016
Charge-hyperscaling violating Lifshitz hydrodynamics from black-holes
Yoshinori Matsuo
(Crete)
Abstract:
Non-equilibrium black hole horizons are considered in scaling theories
with generic Lifshitz invariance and an unbroken U(1) symmetry.
There is also charge-hyperscaling violation
associated with a non-trivial conduction exponent.
The boundary stress tensor is computed and renormalized
and the associated hydrodynamic equations derived.
Upon a non-trivial redefinition of boundary sources associated
with the U(1) gauge field, the equations are mapped to
the standard non-relativistic hydrodynamics equations
coupled to a mass current and an external Newton potential
in accordance with the general theory of [arXiv:1502.00228].
The shear viscosity to entropy ratio is the same as in the relativistic case.
Non-equilibrium black hole horizons are considered in scaling theories
with generic Lifshitz invariance and an unbroken U(1) symmetry.
There is also charge-hyperscaling violation
associated with a non-trivial conduction exponent.
The boundary stress tensor is computed and renormalized
and the associated hydrodynamic equations derived.
Upon a non-trivial redefinition of boundary sources associated
with the U(1) gauge field, the equations are mapped to
the standard non-relativistic hydrodynamics equations
coupled to a mass current and an external Newton potential
in accordance with the general theory of [arXiv:1502.00228].
The shear viscosity to entropy ratio is the same as in the relativistic case.
Posted by: IC
Wed
17 Feb 2016
Brane Brick Models, Toric Calabi-Yau 4-folds and 2d (0,2) Quivers
📍 London
Rak-Kyeong Seong
(KIAS)
Abstract:
In this talk, I will discuss Type IIA brane configurations consisting
of D4-branes suspended between NS5-branes which represent a large
class of 2d (0,2) quiver gauge theories. We call these new
constructions Brane Brick models. These are T-dual to D1-branes over
singular toric Calabi-Yau 4-folds and encode information about the
probed Calabi-Yau geometry as well as the corresponding GLSM. If time
permits, I will present how Brane Brick models naturally realise in
terms of a brane configuration 2d (0,2) Gadde-Gukov-Putrov triality.
In this talk, I will discuss Type IIA brane configurations consisting
of D4-branes suspended between NS5-branes which represent a large
class of 2d (0,2) quiver gauge theories. We call these new
constructions Brane Brick models. These are T-dual to D1-branes over
singular toric Calabi-Yau 4-folds and encode information about the
probed Calabi-Yau geometry as well as the corresponding GLSM. If time
permits, I will present how Brane Brick models naturally realise in
terms of a brane configuration 2d (0,2) Gadde-Gukov-Putrov triality.
Posted by: KCL
Tue
16 Feb 2016
Yang-Mills Theory and the ABC Conjecture
Yang-Hui He
(City)
Abstract:
We establish a precise correspondence between the ABC Conjecture and N=4
super-Yang-Mills theory.
This is achieved by combining three ingredients: (i) Elkies' method of
mapping ABC-triples to elliptic curves in his demonstration that ABC
implies Mordell/Faltings; (ii) an explicit pair of elliptic curve and
associated Belyi map given by Khadjavi-Scharaschkin; and (iii) the fact
that the bipartite brane-tiling/dimer model for a gauge theory with
toric moduli space is a particular dessin d'enfant in the sense of
Grothendieck.
We explore this correspondence for the highest quality ABC-triples as
well as large samples of random triples. The Conjecture itself is mapped
to a statement about the fundamental domain of the toroidal
compactification of the string realization of N=4 SYM.
We establish a precise correspondence between the ABC Conjecture and N=4
super-Yang-Mills theory.
This is achieved by combining three ingredients: (i) Elkies' method of
mapping ABC-triples to elliptic curves in his demonstration that ABC
implies Mordell/Faltings; (ii) an explicit pair of elliptic curve and
associated Belyi map given by Khadjavi-Scharaschkin; and (iii) the fact
that the bipartite brane-tiling/dimer model for a gauge theory with
toric moduli space is a particular dessin d'enfant in the sense of
Grothendieck.
We explore this correspondence for the highest quality ABC-triples as
well as large samples of random triples. The Conjecture itself is mapped
to a statement about the fundamental domain of the toroidal
compactification of the string realization of N=4 SYM.
Posted by: KCL
Thu
11 Feb 2016
Simplifying the Standard Model
Paul Mansfield
(Durham)
Abstract:
I will show that the matter content of the Standard Model takes a simple form
when expressed in terms of world-lines of spinning particles and set this in the context
of an effective string theory of the Standard Model described by tensionless spinning
strings with contact interactions.
I will show that the matter content of the Standard Model takes a simple form
when expressed in terms of world-lines of spinning particles and set this in the context
of an effective string theory of the Standard Model described by tensionless spinning
strings with contact interactions.
Posted by: QMW
Wed
10 Feb 2016
TBA
📍 London
Itamar Shamir
(King's College)
Wed
10 Feb 2016
From holographic transport at finite coupling to bounds on conductivities at strong disorder
Saso Grozadanov
(Leiden)
Abstract:
Holography is a tool that can be most readily applied to studies of transport properties in gauge theories with infinitely strong interactions. Coupling constant corrections can then be incorporated through higher-derivative (alpha-prime) corrections to the supergravity action in the bulk. In the first part of this talk, I will discuss the dependence of higher-order hydrodynamic transport (beyond Navier-Stokes) and the higher-frequency (quasi-normal) spectrum on the coupling constant in duals of Type IIB supergravity and curvature-squared theories. In relation to the membrane paradigm, I will then present higher-order generalisations of the universal "eta over s" relation and universal anomalous conductivities at finite coupling. Recently, studies of holographic transport in the presence of broken translational symmetry and disorder have received much attention. In particular, it has been shown how thermo-electric conductivities can be computed by using the membrane paradigm. Through the power of the membrane paradigm and with a view towards future models of many-body localisation without hydrodynamic transport, in the second part of this talk, I will discuss the proofs of the lower bounds on thermal and electrical conductivities in a large family of holographic theories with arbitrarily strong disorder.
Holography is a tool that can be most readily applied to studies of transport properties in gauge theories with infinitely strong interactions. Coupling constant corrections can then be incorporated through higher-derivative (alpha-prime) corrections to the supergravity action in the bulk. In the first part of this talk, I will discuss the dependence of higher-order hydrodynamic transport (beyond Navier-Stokes) and the higher-frequency (quasi-normal) spectrum on the coupling constant in duals of Type IIB supergravity and curvature-squared theories. In relation to the membrane paradigm, I will then present higher-order generalisations of the universal "eta over s" relation and universal anomalous conductivities at finite coupling. Recently, studies of holographic transport in the presence of broken translational symmetry and disorder have received much attention. In particular, it has been shown how thermo-electric conductivities can be computed by using the membrane paradigm. Through the power of the membrane paradigm and with a view towards future models of many-body localisation without hydrodynamic transport, in the second part of this talk, I will discuss the proofs of the lower bounds on thermal and electrical conductivities in a large family of holographic theories with arbitrarily strong disorder.
Posted by: IC
Tue
9 Feb 2016
Modelling sleep-wake regulation
Anne Skeldon
(Surrey)
Abstract:
Sleep is core to our ability to function and there is increasing evidence that poor or mis-timed sleep increases our risk of cardio vascular disease, type II diabetes, obesity and cognitive decline. In this talk I will discuss the mechanisms that are believed to underlie sleep wake regulation and review some recent mathematical models. In particular, I will focus on age-related changes to sleep and explain how the mathematical models can be used to bring insight into the possible mechanisms that could cause these changes.
Sleep is core to our ability to function and there is increasing evidence that poor or mis-timed sleep increases our risk of cardio vascular disease, type II diabetes, obesity and cognitive decline. In this talk I will discuss the mechanisms that are believed to underlie sleep wake regulation and review some recent mathematical models. In particular, I will focus on age-related changes to sleep and explain how the mathematical models can be used to bring insight into the possible mechanisms that could cause these changes.
Posted by: KCL
Mon
8 Feb 2016
Partition Functions in Even Dimensional AdS via Quasinormal Mode Methods
Cindy Keeler
(NBI)
Abstract:
After a review of the quasinormal mode method for partition function calculation developed by Denef, Hartnoll, and Sachdev, we study a scalar in AdS2. We find a series of zero modes with negative real values of the conformal dimension whose presence indicates a series of poles in the one-loop partition function. The contribution of these poles to the AdS partition function at physical mass values matches previous results. Additionally, extending our results to AdS in any even dimension 2n, we find a similar series of zero modes related to discrete series representations of SO(2n,1), and successfully calculate the one-loop determinant from these modes. Finally, we speculate on the physical meaning of these non-physical-mass modes.
After a review of the quasinormal mode method for partition function calculation developed by Denef, Hartnoll, and Sachdev, we study a scalar in AdS2. We find a series of zero modes with negative real values of the conformal dimension whose presence indicates a series of poles in the one-loop partition function. The contribution of these poles to the AdS partition function at physical mass values matches previous results. Additionally, extending our results to AdS in any even dimension 2n, we find a similar series of zero modes related to discrete series representations of SO(2n,1), and successfully calculate the one-loop determinant from these modes. Finally, we speculate on the physical meaning of these non-physical-mass modes.
Posted by: IC
Wed
3 Feb 2016
Holographic cosmology and Planck data
Kostas Skenderis
(Southampton)
Abstract:
I will present holographic models for the very early Universe, the period usually associated with inflation, and compare the predictions of these models against Planck 2015 data. Within the holographic framework the early Universe is described by a three dimensional QFT. Conventional inflation is included in this framework as strong coupled QFT
while qualitatively new models arise when the QFT has weak or intermediate coupling. The weakly coupled models describe a very quantum early Universe and it turns out that these models fit the Planck data remarkably well, providing an alternative to LambdaCDM. New models based on QFT at intermediate coupling may be constructed using Lattice methods and I will also describe on-going work in this direction.
I will present holographic models for the very early Universe, the period usually associated with inflation, and compare the predictions of these models against Planck 2015 data. Within the holographic framework the early Universe is described by a three dimensional QFT. Conventional inflation is included in this framework as strong coupled QFT
while qualitatively new models arise when the QFT has weak or intermediate coupling. The weakly coupled models describe a very quantum early Universe and it turns out that these models fit the Planck data remarkably well, providing an alternative to LambdaCDM. New models based on QFT at intermediate coupling may be constructed using Lattice methods and I will also describe on-going work in this direction.
Posted by: KCL
Tue
2 Feb 2016
Supersymmetric gauge theories, localization and holography
Dario Martelli
(King's)
Abstract:
I will discuss some exact results in supersymmetric field theories, focussing on the localization technique in supersymmetric gauge theories and its interplay with holography.
I will discuss some exact results in supersymmetric field theories, focussing on the localization technique in supersymmetric gauge theories and its interplay with holography.
Posted by: KCL
January 2016
Thu
28 Jan 2016
One loop partition function of six dimensional conformal gravity using heat kernel on AdS_2n
Iva Lovrekovic
(Vienna)
Abstract:
We compute the heat kernel for the Laplacians of symmetric transverse traceless fields of arbitrary spin on the AdS background in even number of dimensions using the group theoretic approach and apply it on the partition function of six dimensional conformal gravity. The obtained partition function consists of the Einstein gravity, conformal ghost, partially massless mode and massive mode.
We compute the heat kernel for the Laplacians of symmetric transverse traceless fields of arbitrary spin on the AdS background in even number of dimensions using the group theoretic approach and apply it on the partition function of six dimensional conformal gravity. The obtained partition function consists of the Einstein gravity, conformal ghost, partially massless mode and massive mode.
Posted by: IC
Thu
28 Jan 2016
Perturbative and numerical aspects of string sigma models
Lorenzo Bianchi
(DESY Hamburg)
Abstract:
In the last fifteen years an extensive and successful program has been carried out, consisting in the application of integrability techniques to the study of the AdS/CFT correspondence in the planar limit. In this talk we focus on a particular string background corresponding, on the dual side, to the expectation value of a cusped Wilson line. Recently the study of this background has been boosted by the OPE program for polygonal Wilson loops and scattering amplitudes. In this talk we consider the quantum fluctuations of the worldsheet theory around the null cusp classical solution and we investigate various quantities of physical interest (free energy, dispersion relation, S-matrix) in the perturbative expansion at strong coupling. We also propose a possible discretization of this model which can be used to study the theory non-perturbatively through numerical lattice simulations.
In the last fifteen years an extensive and successful program has been carried out, consisting in the application of integrability techniques to the study of the AdS/CFT correspondence in the planar limit. In this talk we focus on a particular string background corresponding, on the dual side, to the expectation value of a cusped Wilson line. Recently the study of this background has been boosted by the OPE program for polygonal Wilson loops and scattering amplitudes. In this talk we consider the quantum fluctuations of the worldsheet theory around the null cusp classical solution and we investigate various quantities of physical interest (free energy, dispersion relation, S-matrix) in the perturbative expansion at strong coupling. We also propose a possible discretization of this model which can be used to study the theory non-perturbatively through numerical lattice simulations.
Posted by: QMW
Tue
26 Jan 2016
Eigenstate Phase Transitions for Strong Zero Modes
Paul Fendley
(Oxford)
Abstract:
Traditionally, most studies of quantum many-body systems have been mainly concerned with properties of the states of low-lying energy. Recently, however, fascinating features of the full energy spectrum have been uncovered. Among these are eigenstate phase transitions, where sharp transitions occur not only in the ground state, but in all the states. I describe a simple example of such, a transition for a strong zero mode in the XYZ spin chain. The strong zero mode is an operator that pairs states in different symmetry sectors, resulting in identical spectra up to exponentially small finite-size corrections. Such pairing occurs in the Ising/Majorana fermion chain and possibly in parafermionic systems and strongly disordered many-body localized phases. My proof here shows that the strong zero mode occurs in a clean interacting system, and that it possesses some remarkable structure – despite being a rather elaborate operator, it squares to the identity.
Traditionally, most studies of quantum many-body systems have been mainly concerned with properties of the states of low-lying energy. Recently, however, fascinating features of the full energy spectrum have been uncovered. Among these are eigenstate phase transitions, where sharp transitions occur not only in the ground state, but in all the states. I describe a simple example of such, a transition for a strong zero mode in the XYZ spin chain. The strong zero mode is an operator that pairs states in different symmetry sectors, resulting in identical spectra up to exponentially small finite-size corrections. Such pairing occurs in the Ising/Majorana fermion chain and possibly in parafermionic systems and strongly disordered many-body localized phases. My proof here shows that the strong zero mode occurs in a clean interacting system, and that it possesses some remarkable structure – despite being a rather elaborate operator, it squares to the identity.
Posted by: KCL
Wed
20 Jan 2016
Gronewold-Moyal Mechanics: From quantum mechanics to higher spin gravity and matrix models
📍 London
Mauricio Valenzuela
(Chile Austral U., Valdivia)
Abstract:
The goal of this talk is to show some uses of the Gronewold-Moyal product in physics and new applications.
In the first part of this talk we review the approach of Gronewold and Moyal in the quantization of classical systems. Then we remark algebraic aspects related to the representation of symplectic algebras and extensions of Anti-de-Sitter algebras. Subsequently we describe how these aspects are used in higher spin gravity.
In the second part of this talk we present some new advances. We quantize a particular class of algebraic varieties, involving multivectors, and which contains Minkowski space slices. We show that these non-commutative geometries are solutions of known matrix models and some simple extensions of them. Then we present new models which describe the dynamics of extended objects in close resemblance to the equations of Hamiltonian systems. We also introduce statistical distributions in these spaces which encode their coordinates spectra.
The goal of this talk is to show some uses of the Gronewold-Moyal product in physics and new applications.
In the first part of this talk we review the approach of Gronewold and Moyal in the quantization of classical systems. Then we remark algebraic aspects related to the representation of symplectic algebras and extensions of Anti-de-Sitter algebras. Subsequently we describe how these aspects are used in higher spin gravity.
In the second part of this talk we present some new advances. We quantize a particular class of algebraic varieties, involving multivectors, and which contains Minkowski space slices. We show that these non-commutative geometries are solutions of known matrix models and some simple extensions of them. Then we present new models which describe the dynamics of extended objects in close resemblance to the equations of Hamiltonian systems. We also introduce statistical distributions in these spaces which encode their coordinates spectra.
Posted by: KCL
Wed
20 Jan 2016
Polygon Seminar: SUSY field theories and matrix models
Nadav Drukker
(KCL)
Abstract:
Matrix models are toy models for quantum field theories. They can be extremely complicated but can also be solved in a variety of ways. In my talk I will discuss general properties of matrix models and their solutions and focus on particular matrix models that arise in the study of 4d SUSY field theories. Those matrix models describe the index of the field theory, counting the number of states of the theory (with + sign for a boson and - for a fermion) and have been known for over 10 years. Though they look very complicated I will show how some simple tricks allow in certain cases to solve those matrix models exactly in terms of elementary functions. My talk will focus on the matrix model calculation and no specialized knowledge of SUSY field theories or indices would be required to follow it.
Matrix models are toy models for quantum field theories. They can be extremely complicated but can also be solved in a variety of ways. In my talk I will discuss general properties of matrix models and their solutions and focus on particular matrix models that arise in the study of 4d SUSY field theories. Those matrix models describe the index of the field theory, counting the number of states of the theory (with + sign for a boson and - for a fermion) and have been known for over 10 years. Though they look very complicated I will show how some simple tricks allow in certain cases to solve those matrix models exactly in terms of elementary functions. My talk will focus on the matrix model calculation and no specialized knowledge of SUSY field theories or indices would be required to follow it.
Posted by: IC
Thu
14 Jan 2016
Generalising Calabi-Yau for generic flux backgrounds
Anthony Ashmore
(Imperial College)
Abstract:
Calabi-Yau manifolds without flux are perhaps the best-known supergravity backgrounds that leave some supersymmetry unbroken. The supersymmetry conditions on such spaces can be rephrased as the existence and integrability of a particular geometric structure. When fluxes are allowed, the conditions are more complicated and the analogue of the geometric structure is not well understood.
In this talk, I will define the analogue of Calabi-Yau geometry for generic D=4, N=2 backgrounds with flux in both type II and eleven-dimensional supergravity. The geometry is characterised by a pair of G-structures in 'exceptional generalised geometry' that interpolate between complex, symplectic and hyper-Kahler geometry. Supersymmetry is then equivalent to integrability of the structures, which appears as moment maps for diffeomorphisms and gauge transformations. Similar structures also appear in D=5 and D=6 backgrounds with eight supercharges.
As a simple application, I will discuss the case of AdS5 backgrounds in type IIB, where deformations of these geometric structures give exactly marginal deformations of the dual field theories.
Calabi-Yau manifolds without flux are perhaps the best-known supergravity backgrounds that leave some supersymmetry unbroken. The supersymmetry conditions on such spaces can be rephrased as the existence and integrability of a particular geometric structure. When fluxes are allowed, the conditions are more complicated and the analogue of the geometric structure is not well understood.
In this talk, I will define the analogue of Calabi-Yau geometry for generic D=4, N=2 backgrounds with flux in both type II and eleven-dimensional supergravity. The geometry is characterised by a pair of G-structures in 'exceptional generalised geometry' that interpolate between complex, symplectic and hyper-Kahler geometry. Supersymmetry is then equivalent to integrability of the structures, which appears as moment maps for diffeomorphisms and gauge transformations. Similar structures also appear in D=5 and D=6 backgrounds with eight supercharges.
As a simple application, I will discuss the case of AdS5 backgrounds in type IIB, where deformations of these geometric structures give exactly marginal deformations of the dual field theories.
Posted by: QMW
Wed
13 Jan 2016
Negativities, entanglement structures of qubit systems and holography
Massimiliano Rota
(Durham)
Abstract:
Entanglement entropy is a very important quantity in holography, nevertheless it is only a measure of the total amount of entanglement between two complementary subsystems in a global pure state. A more detailed knowledge about the pattern of entanglement is essential for a deeper understanding of the relation between bulk geometry and quantum information in the boundary theory. I will discuss how negativities and other measures can be used in this context focusing in particular on qubit systems for which a classification of possible entanglement structures is available.
Entanglement entropy is a very important quantity in holography, nevertheless it is only a measure of the total amount of entanglement between two complementary subsystems in a global pure state. A more detailed knowledge about the pattern of entanglement is essential for a deeper understanding of the relation between bulk geometry and quantum information in the boundary theory. I will discuss how negativities and other measures can be used in this context focusing in particular on qubit systems for which a classification of possible entanglement structures is available.
Posted by: IC