Triangle Seminars
December 2011
Wed
14 Dec 2011
Holographic duals for N=4 SYM on AdS_4 and branes ending on branes
Ofer Aharony
(Weizmann Institute)
Abstract:
I will start by discussing the 4d N=4 supersymmetric Yang-Mills theory on two spaces with a boundary - a half-line (times three infinite dimensions) and four dimensional anti-de Sitter space. I will review in detail the possible choices of boundary conditions for this theory, and then exhibit the solutions of string theory (supergravity) that are holographically dual to the N=4 SYM theory on these spaces. The same methods used to obtain these duals can also be used to find duals for 3d N=4 and 4d N=2 superconformal field theories that appear in brane configurations, and I will discuss these solutions as well.
I will start by discussing the 4d N=4 supersymmetric Yang-Mills theory on two spaces with a boundary - a half-line (times three infinite dimensions) and four dimensional anti-de Sitter space. I will review in detail the possible choices of boundary conditions for this theory, and then exhibit the solutions of string theory (supergravity) that are holographically dual to the N=4 SYM theory on these spaces. The same methods used to obtain these duals can also be used to find duals for 3d N=4 and 4d N=2 superconformal field theories that appear in brane configurations, and I will discuss these solutions as well.
Posted by: QMW
Wed
14 Dec 2011
Gravity duals of supersymmetric gauge theories on curved manifolds
James Sparks
(Oxford U.)
Fri
9 Dec 2011
Spinning Conformal Correlators and Blocks
Slava Rychkov
(LPTENS)
Wed
7 Dec 2011
Instanton - a window into physics of M5-branes
📍 London
Sungjay Lee
(DAMTP Cambridge)
Abstract:
Instantons and W-bosons in 5d N=2 Yang-Mills theory arise from a circle compactification of the 6d (2,0) theory as Kaluza-Klein modes and winding self-dual strings, respectively. We study an index which counts BPS instantons with electric charges in Coulomb and symmetric phases. We first prove the existence of unique threshold bound state of U(1) instantons for any instanton number. By studying SU(N) self-dual strings in the Coulomb phase, we find novel momentum-carrying degrees on the worldsheet. The total number of these degrees equals the anomaly coefficient of SU(N) (2,0) theory. We finally propose that our index can be used to study the symmetric phase of this theory, and provide an interpretation as the superconformal index of the sigma model on instanton moduli space.
Instantons and W-bosons in 5d N=2 Yang-Mills theory arise from a circle compactification of the 6d (2,0) theory as Kaluza-Klein modes and winding self-dual strings, respectively. We study an index which counts BPS instantons with electric charges in Coulomb and symmetric phases. We first prove the existence of unique threshold bound state of U(1) instantons for any instanton number. By studying SU(N) self-dual strings in the Coulomb phase, we find novel momentum-carrying degrees on the worldsheet. The total number of these degrees equals the anomaly coefficient of SU(N) (2,0) theory. We finally propose that our index can be used to study the symmetric phase of this theory, and provide an interpretation as the superconformal index of the sigma model on instanton moduli space.
Posted by: KCL
Tue
6 Dec 2011
Cosmology and the Fab Four
Ed Copeland
(Nottingham U.)
Abstract:
We briefly review some models of dark energy. We start with the cosmological constant including models arising in string theory, before discussing dynamical models where a scalar field may be responsible for the observed late time acceleration. The possibility that we are not fully in control of the gravity sector is discussed and the possibility that the acceleration may be some manifestation of modified gravity on large scales is shown. All cases require some degree of fine tuning for the models to be compatible with observation. Finally, we briefly discuss some recent fun work involving scalar-tensor theories of gravity in which a self-tuning mechanism exists leading to the same late time cosmology independently of the size of the cosmological constant. Solutions include having radiation and matter dominated like regimes whilst the energy density remains dominated by a cosmological constant.
We briefly review some models of dark energy. We start with the cosmological constant including models arising in string theory, before discussing dynamical models where a scalar field may be responsible for the observed late time acceleration. The possibility that we are not fully in control of the gravity sector is discussed and the possibility that the acceleration may be some manifestation of modified gravity on large scales is shown. All cases require some degree of fine tuning for the models to be compatible with observation. Finally, we briefly discuss some recent fun work involving scalar-tensor theories of gravity in which a self-tuning mechanism exists leading to the same late time cosmology independently of the size of the cosmological constant. Solutions include having radiation and matter dominated like regimes whilst the energy density remains dominated by a cosmological constant.
Posted by: IC
Fri
2 Dec 2011
Thermal Stability of Quantum Horizons
Parthasarathi Majumdar
(SINP, Kolkata)
Thu
1 Dec 2011
Holographic three-point functions
Tristan McLoughlin
(AEI)
November 2011
Tue
29 Nov 2011
Generalised geometry and E_11
Peter West
(King's College)
Abstract:
We will review the conjecture that the Kac-Moody Symmetry E_11 is an underlying symmetry of strings and branes. We will show that it leads to a generalised geometry involving an extension of our usual formulation of space-time.
We will review the conjecture that the Kac-Moody Symmetry E_11 is an underlying symmetry of strings and branes. We will show that it leads to a generalised geometry involving an extension of our usual formulation of space-time.
Posted by: IC
Fri
25 Nov 2011
Surprises with Interacting High Spin Particles
Massimo Porrati
(New York University)
Abstract:
This colloquium reviews old and new no go theorems that severely constrain possible interactions of massless high spin particles. Massive particles can interact with gauge fields and gravity, but often they are plagued by pathologies such as superluminal propagation in nontrivial backgrounds. The last part of the talk uses the example of open string theory to show that such pathologies can be avoided by an appropriate choice of non-minimal interactions.
This colloquium reviews old and new no go theorems that severely constrain possible interactions of massless high spin particles. Massive particles can interact with gauge fields and gravity, but often they are plagued by pathologies such as superluminal propagation in nontrivial backgrounds. The last part of the talk uses the example of open string theory to show that such pathologies can be avoided by an appropriate choice of non-minimal interactions.
Posted by: IC
Thu
24 Nov 2011
tba
matthew buican
(cern)
Wed
23 Nov 2011
Branes and Monopoles
📍 London
Eric Bergshoeff
(University of Groningen)
Abstract:
We show that in order to understand the higher-dimensional origin of all supersymmetric branes in (toroidally) compactified string theory one needs to extend the family of branes with an additional set of so-called ``generalized monopoles''. We will show what these monopoles are and how they lead to interesting ``wrapping rules'' for the branes in string theory.
We show that in order to understand the higher-dimensional origin of all supersymmetric branes in (toroidally) compactified string theory one needs to extend the family of branes with an additional set of so-called ``generalized monopoles''. We will show what these monopoles are and how they lead to interesting ``wrapping rules'' for the branes in string theory.
Posted by: KCL
Wed
23 Nov 2011
Holography of Einstein-Maxwell-Dilaton theories and applications to Condensed Matter Systems
Blaise Gouteraux
(Paris 7)
Thu
17 Nov 2011
ABJM theory as a Fermi gas
pavel putrov
(geneva university)
Abstract:
The partition function on the three-sphere of many
supersymmetric Chern-Simons-matter theories reduces, by localization, to a matrix model.
In this talk I will describe a new method to study
these models in the M-theory limit, but at all orders in the 1/N expansion. The method is based on reformulating the matrix model as the partition function of a Fermi gas. This new approach leads to a completely elementary derivation of the N^{3/2} behavior for ABJM theory and other quiver Chern-Simons-matter theories. In addition, the full series of 1/N corrections to the original matrix integral can be
simply determined by a next-to-leading calculation in the semiclassical expansion of the quantum gas.
The partition function on the three-sphere of many
supersymmetric Chern-Simons-matter theories reduces, by localization, to a matrix model.
In this talk I will describe a new method to study
these models in the M-theory limit, but at all orders in the 1/N expansion. The method is based on reformulating the matrix model as the partition function of a Fermi gas. This new approach leads to a completely elementary derivation of the N^{3/2} behavior for ABJM theory and other quiver Chern-Simons-matter theories. In addition, the full series of 1/N corrections to the original matrix integral can be
simply determined by a next-to-leading calculation in the semiclassical expansion of the quantum gas.
Posted by: QMW
Wed
16 Nov 2011
Minimal Model Holography
📍 London
Matthias Gaberdiel
(ETH Zürich)
Wed
16 Nov 2011
Spin Chains and Holography at the Veneziano limit
📍 London
Elli Pomoni
(Humboldt)
Abstract:
N = 2 SuperConformal QCD is perhaps the simplest theory outside the N = 4 "universality class" that we can attempt to study holographically. It is moreover continuously connected to the N = 4 class by an interpolating family of N = 2 SCFT. Careful analysis of its chiral spectrum points towards a gravity dual description via a non-critical string background. We then turn to the study of spin chains. The complete one-loop Hamiltonian and some higher-loop results already reveal a rich dynamics. We present past results and current progress.
N = 2 SuperConformal QCD is perhaps the simplest theory outside the N = 4 "universality class" that we can attempt to study holographically. It is moreover continuously connected to the N = 4 class by an interpolating family of N = 2 SCFT. Careful analysis of its chiral spectrum points towards a gravity dual description via a non-critical string background. We then turn to the study of spin chains. The complete one-loop Hamiltonian and some higher-loop results already reveal a rich dynamics. We present past results and current progress.
Posted by: KCL
Fri
11 Nov 2011
Holographic Uniformization
Nikolay Bobev
(Stony Brook)
Thu
10 Nov 2011
tba
diego marquis
Wed
9 Nov 2011
Cubic interactions for simple mixed-symmetry fields in AdS
📍 London
Nicolas Boulanger
(University of Mons)
Abstract:
Recent results (arXiv:1107.1872 and arXiv:1107.5028) will be presented
about nonabelian interactions for simple mixed-symmetry gauge fields in
AdS background.
Recent results (arXiv:1107.1872 and arXiv:1107.5028) will be presented
about nonabelian interactions for simple mixed-symmetry gauge fields in
AdS background.
Posted by: KCL
Wed
9 Nov 2011
Holography of the tachyon
Andrei Parnachev
(Leiden U.)
Thu
3 Nov 2011
BPS Saturated Objects in String Theory: K3 Elliptic Genus and Igusa Cusp Form chi10
stefan Hohenegger
(MPI)
Abstract:
In this talk I will discuss the elliptic genus of K3 (\phi_{K3}) both from a conformal field theory and an effective action point of view as an example of a BPS saturated quantity in string theory. In the former approach I will give evidence for an action of the Mathieu group M_{24} on the space of BPS states contributing to \phi_{K3} (Mathieu moonshine). On the effective action side I will present a new series of 1/4 BPS saturated one-loop amplitudes in type II string theory on K3xT^2 whose integrand can be related to derivatives of \phi_{K3}. I will evaluate explicitly a generating functional for this class of amplitudes and show that it is captured by the weight ten Igusa cusp form of Sp(4,Z). I conclude by speculating on possible algebraic implications of these results on the space of BPS states of the N=4 type II compactification.
In this talk I will discuss the elliptic genus of K3 (\phi_{K3}) both from a conformal field theory and an effective action point of view as an example of a BPS saturated quantity in string theory. In the former approach I will give evidence for an action of the Mathieu group M_{24} on the space of BPS states contributing to \phi_{K3} (Mathieu moonshine). On the effective action side I will present a new series of 1/4 BPS saturated one-loop amplitudes in type II string theory on K3xT^2 whose integrand can be related to derivatives of \phi_{K3}. I will evaluate explicitly a generating functional for this class of amplitudes and show that it is captured by the weight ten Igusa cusp form of Sp(4,Z). I conclude by speculating on possible algebraic implications of these results on the space of BPS states of the N=4 type II compactification.
Posted by: QMW
Wed
2 Nov 2011
Landscape of consistent reductions with applications
📍 London
Davide Cassani
(KCL)
Abstract:
Consistent truncations have proved to be powerful tools in the construction of new string theory solutions. Recently, they have been employed in the holographic description of condensed matter systems. In the talk, I will present a rich class of supersymmetric consistent truncations of higher-dimensional supergravity which are based on geometric structures, focusing on the tri-Sasakian case. Then I will discuss some applications, including a general result relating AdS backgrounds to solutions with non-relativistic Lifshitz symmetry.
Consistent truncations have proved to be powerful tools in the construction of new string theory solutions. Recently, they have been employed in the holographic description of condensed matter systems. In the talk, I will present a rich class of supersymmetric consistent truncations of higher-dimensional supergravity which are based on geometric structures, focusing on the tri-Sasakian case. Then I will discuss some applications, including a general result relating AdS backgrounds to solutions with non-relativistic Lifshitz symmetry.
Posted by: KCL
Wed
2 Nov 2011
TBA
Dario Martelli
(King's College)
October 2011
Thu
27 Oct 2011
tba
stefano cremonesi
(imperial)
Wed
26 Oct 2011
Black hole instabilities and local Penrose inequalities
📍 London
Harvey Reall
(DAMTP Cambridge)
Abstract:
We explain how inequalities similar to the Penrose inequality provide
a simple way of demonstrating classical instability of certain black
hole solutions.
We explain how inequalities similar to the Penrose inequality provide
a simple way of demonstrating classical instability of certain black
hole solutions.
Posted by: KCL
Wed
26 Oct 2011
Instantons from branes and Higgs vacua of N=1 theories
Anatoly Dymarsky
(Princeton U.)
Tue
25 Oct 2011
Instantons, Integrability and N=2 SUSY: The Basics
Tim Hollowood
(Swansea)
Abstract:
This talk will give a pedagogical account of the role played
by integrability and instantons in N=2 SUSY gauge theories leading
to recent understanding of what it means to quantize the integrable
system.
This talk will give a pedagogical account of the role played
by integrability and instantons in N=2 SUSY gauge theories leading
to recent understanding of what it means to quantize the integrable
system.
Posted by: KCL
Wed
19 Oct 2011
Super Yang-Mills Amplitudes in Flatland
Donovan Young
(NBI)
Abstract:
I will discuss scattering amplitudes in N=2,4,8 SYM in three-dimensions, concentrating on the N=8 case, with an emphasis on which properties of the
N=4, D=4 SYM amplitudes survive under dimensional reduction. The on-shell
supersymmetry algebra makes the SO(N) symmetry of the amplitudes manifest,
while the Lagrangian displays only manifest SO(N-1) symmetry. I will also discuss
the possibility of non-local Yangian-type symmetry, connections to BLG,
and some perspectives on loop level results. Based on 1103.0786 / 1109.2792.
I will discuss scattering amplitudes in N=2,4,8 SYM in three-dimensions, concentrating on the N=8 case, with an emphasis on which properties of the
N=4, D=4 SYM amplitudes survive under dimensional reduction. The on-shell
supersymmetry algebra makes the SO(N) symmetry of the amplitudes manifest,
while the Lagrangian displays only manifest SO(N-1) symmetry. I will also discuss
the possibility of non-local Yangian-type symmetry, connections to BLG,
and some perspectives on loop level results. Based on 1103.0786 / 1109.2792.
Posted by: KCL
Wed
19 Oct 2011
Dimer Models, Integrable Systems and Gauge Theory
Sebastian Franco
(Durham)
Abstract:
Dimer models are typically studied in condesed matter
physics and combinatorics. The correspondence between
dimer models, toric Calabi-Yaus and quiver gauge theories
on D-branes has had a profound impact in areas ranging
from string phenomenology to mathematics. Today I will discuss
a recently discovered correspondence between dimer models
and integrable systems.
Dimer models are typically studied in condesed matter
physics and combinatorics. The correspondence between
dimer models, toric Calabi-Yaus and quiver gauge theories
on D-branes has had a profound impact in areas ranging
from string phenomenology to mathematics. Today I will discuss
a recently discovered correspondence between dimer models
and integrable systems.
Posted by: KCL
Tue
18 Oct 2011
Permutations, Strings and Feynman Graphs
Sanjaye Ramgoolam
(QMUL)
Abstract:
Abstract :
Feynman Graph counting in Quantum Field Theory (QFT) can be formulated in terms
of symmetric groups. This leads to expressions for
graph counting and symmetry factors in terms of topological transition
amplitudes for strings with a cylinder target, related to two dimensional
topological field theory. The details of the interactions in the QFT
are encoded in the boundary conditions which specify
how the strings wind around circles. The QFTs discussed include scalar field theories and QED, where there is no large gauge group.
Abstract :
Feynman Graph counting in Quantum Field Theory (QFT) can be formulated in terms
of symmetric groups. This leads to expressions for
graph counting and symmetry factors in terms of topological transition
amplitudes for strings with a cylinder target, related to two dimensional
topological field theory. The details of the interactions in the QFT
are encoded in the boundary conditions which specify
how the strings wind around circles. The QFTs discussed include scalar field theories and QED, where there is no large gauge group.
Posted by: KCL
Wed
12 Oct 2011
Non-Hermitian Hamiltonian systems and antilinear deformations of integrable systems
📍 London
Andreas Fring
(City University)
Abstract:
I will provide a brief general introduction into non-Hermitian Hamiltonian systems with real eigenvalue spectra, arguing that they represent well defined self consistent physical systems. Such type of models possess usually an antilinear symmetry, as for instance PT-invariance (simultaneous parity and time reversal) and/or are quasi/pseudo Hermitian. Most crucial is that they allow for a consistent quantum mechanical framework possessing a unitary time evolution. The general framework will be applied to some integrable models, such a quantum spin chains, classical integrable systems associated to differential equations and Calogero-Moser-Sutherland models. I will present some recent results.
I will provide a brief general introduction into non-Hermitian Hamiltonian systems with real eigenvalue spectra, arguing that they represent well defined self consistent physical systems. Such type of models possess usually an antilinear symmetry, as for instance PT-invariance (simultaneous parity and time reversal) and/or are quasi/pseudo Hermitian. Most crucial is that they allow for a consistent quantum mechanical framework possessing a unitary time evolution. The general framework will be applied to some integrable models, such a quantum spin chains, classical integrable systems associated to differential equations and Calogero-Moser-Sutherland models. I will present some recent results.
Posted by: KCL
Wed
12 Oct 2011
Generic String/M theory predictions for the LHC and Dark Matter
📍 London
Bobby Acharya
(KCL)
Tue
11 Oct 2011
Forcing, independence, Plato and multiuniverses of set theory
Mirna Dzamonja
(University of East Anglia)
Abstract:
We shall talk generally about the state of the art in set theory and try to explain to what extent the independence results in set theory influence our understanding of mathematical foundations. The talk will start rather generally and will build up to describe some current research directions.
We shall talk generally about the state of the art in set theory and try to explain to what extent the independence results in set theory influence our understanding of mathematical foundations. The talk will start rather generally and will build up to describe some current research directions.
Posted by: KCL
Wed
5 Oct 2011
Conifold Geometries and NS5-branes
📍 London
Jock McOrist
(DAMTP)
Tue
4 Oct 2011
Derivatives and Credit Contagion in Interconnected Networks
Reimer Kuehn
(King's)
Abstract:
The importance of adequately modeling credit risk has once again been
highlighted in the recent financial crisis. Defaults tend to cluster
around times of economic stress due to poor macro-economic conditions,
but also by directly triggering each other through contagion. Although
credit default swaps have radically altered the dynamics of contagion
for more than a decade, models quantifying their impact on systemic risk
are still missing. Here, we examine contagion through credit default
swaps in a stylized economic network of corporates and financial
institutions. We analyse such a system using a stochastic setting, which
allows us to exploit limit theorems to exactly solve the contagion
dynamics for the entire system. Our analysis shows that CDS, when used
to expand banks' loan books (arguing that CDS would offload the
additional risks from banks' balance sheets), can actually lead to
greater instability of the entire network in times of economic stress,
by creating additional contagion channels. This can lead to considerably
enhanced probabilities for the occurrence of very large losses and very
high default rates in the system. Our approach adds a new dimension to
research on credit contagion, and could feed into a rational
underpinning of an improved regulatory framework for credit derivatives.
The importance of adequately modeling credit risk has once again been
highlighted in the recent financial crisis. Defaults tend to cluster
around times of economic stress due to poor macro-economic conditions,
but also by directly triggering each other through contagion. Although
credit default swaps have radically altered the dynamics of contagion
for more than a decade, models quantifying their impact on systemic risk
are still missing. Here, we examine contagion through credit default
swaps in a stylized economic network of corporates and financial
institutions. We analyse such a system using a stochastic setting, which
allows us to exploit limit theorems to exactly solve the contagion
dynamics for the entire system. Our analysis shows that CDS, when used
to expand banks' loan books (arguing that CDS would offload the
additional risks from banks' balance sheets), can actually lead to
greater instability of the entire network in times of economic stress,
by creating additional contagion channels. This can lead to considerably
enhanced probabilities for the occurrence of very large losses and very
high default rates in the system. Our approach adds a new dimension to
research on credit contagion, and could feed into a rational
underpinning of an improved regulatory framework for credit derivatives.
Posted by: KCL