At non-zero baryon density, simulations of lattice QCD face a "sign problem" which prevents significant progress. In particular, the phase diagram of QCD as a function of temperature and chemical potential remains largely unknown. I recall the nature of the sign problem, the approaches used to circumvent it at small density, and point to a possible direction for progress.

Herbert Neuberger (Rutgers)
Non-analyticity in scale in the planar limit of QCD

Using methods of numerical Lattice Gauge Theory we show that in the limit of a large number of colors, properly regularized Wilson loops have an eigenvalue distribution which changes non-analytically as the overall size of the loop is increased. This establishes a large-$N$ phase transition in continuum planar gauge theory, a fact whose precise implications remain to be worked out.

Frans Pretorius (Princeton)
A new numerical approach to evolution of 5D asymptotically AdS spacetimes

I will describe a new numerical effort to solve Einstein gravity in 5-dimensional asymptotically Anti de Sitter spacetimes. The motivation is the gauge/gravity duality of string theory, with eventual application to scenarios (for example heavy ion collisions) that on the gravity side are described by dynamical, strong-field solutions. As a first step towards modeling such phenomena, we initially focus on spacetimes with SO(3) symmetry in the bulk; i.e., axisymmetric gravity, dual to plasma dynamics on the boundary with spherical or special conformal symmetry. As a test application we explore quasi-normal ringdown of highly deformed black holes in the bulk, and examine the degree to which the expectation value of the dual boundary stress tensor agrees with that of a conformal fluid.

David Garfinkle(Oakland)
Novel(?) numerical methods for AdS gravitational collapse

It is to be expected that new numerical methods will be needed to do simulations of gravitational collapse in 5 dimensions and with AdS boundary conditions. Nonetheless, it is helpful to see how far we can get using the sort of methods that have worked for GR in 4 dimensions. This talk will presents results for spherically symmetric gravitational collapse of a scalar field in AdS 5 in both global and Poincare coordinates.

Simon Catterall(Syracuse)
Twisted lattice supersymmetry: a status report

I will briefly review the construction of lattice Yang Mills theories which exhibit invariance under one or more twisted supersymmetries at non zero lattice spacing focusing in particular on a lattice model which targets N=4 YM in the naive continuum limit. I will show that the structure of the lattice model is remarkably similar to its continuum counterpart; the moduli space is not lifted to all orders in perturbation theory and the one loop beta function vanishes. I will then describe how the model may be simulated using standard Monte Carlo techniques borrowed from lattice QCD and hence how lattice studies can be used to probe the non perturbative structure of the theory and test aspects of the AdS/CFT correspondence.

Asato Tsuchiya(Shizuoka)
Expanding (3+1)-dimensional universe from a matrix model for superstrings

We reconsider the matrix model formulation of type IIB superstring theory in (9+1)-dimensional space-time. Unlike the previous works in which the Wick rotation was used to make the model well-defined, we regularize
the Lorentzian model by introducing infrared cutoffs in both the spatial and temporal directions. Monte Carlo studies reveal that the two cutoffs can be removed in the large-N limit and that the theory thus obtained has no parameters
other than one scale parameter. Moreover, we find that three out of nine spatial directions start to expand at some "critical time", after which the space has SO(3) symmetry instead of SO(9).

Paul Chesler(MIT)
Dynamical Hawking radiation and holographic thermalization

Holography provides a powerful tool to study non-equilibrium dynamics in strongly coupled quantum field theories, mapping challenging D dimensional quantum dynamics on to semi-classical gravity in D+1 dimensions. One interesting quantum field theory process to study is the creation and thermalization of a D = 4 strongly coupled quark-gluon plasma. Heavy ion collisions at RHIC and the LHC suggest that quark-gluon plasma can be created and thermalize in a time as short as 1 fm/c, the time it takes for light to traverse the diameter of a proton. Understanding the dynamics responsible for such rapid thermalization is a challenge using traditional perturbative field theory. Via holography, the creation of a quark-gluon plasma maps into the process of gravitational collapse and black brane formation. The thermalization of the quark-gluon plasma maps into the relaxation of the black brane geometry and thermalization of its Hawking radiation. I will describe new techniques for studying holographic thermalization and present results for thermalization times and mechanisms.

Liza Huijse (Harvard)
The power of supersymmetry in a lattice model for strongly interacting fermions

We consider a class of models for strongly interacting fermions that possesses supersymmetry. The benefit of incorporating this property turns out to be twofold. First, the supersymmetry leads to a considerable degree of analytic control, allowing the rigorous derivation of quite a few results, in particular on quantum ground states. Second, it induces a subtle interplay between kinetic and potential terms, which gives rise to various interesting features, such as quantum criticality and superfrustration, characterized by an extensive ground state entropy. In this talk, I will give an overview of the main results for this system, while discussing the key techniques that are available due to supersymmetry.

Mithat Unsal (Stanford)
Gauge dynamics and new instanton, bion and renormalon effects

I discuss the dynamics of four dimensional gauge theories with adjoint fermions for general gauge groups, both in perturbation theory and non-perturbatively, by using circle compactification with periodic boundary conditions for the fermions. There are new gauge phenomena, and new instanton effects. I will describe whether we can actually make sense of gauge theory in continuum. In compactified theory, I will give evidence that the elusive IR renormalons (for which no semi-classical configuration is known) of 't Hooft may have a semi-classical incarnation.
This is a molecule that Argyres and I refer to as "neutral bion". It carries zero topological charge and zero magnetic charge, and it corresponds to a pole in the Borel plane much closer to origin (by a factor of N) than the 4d instanton-anti-instanton pole. We recently derived this class of molecules by generalizing an old work of Bogomolny and Zinn-Justin from quantum mechanics to quantum field theory. I suspect we may have a chance to understand this theory in continuum.

Gary Horowitz (UCSB)
Instability of anti-de Sitter Spacetime

I will describe recent evidence that anti-de Sitter spacetime is nonlinearly unstable. Generic small but finite perturbations eventually form small black holes. There are special solutions, called geons, which remain nonsingular and do not collapse. I will also describe (weaker) evidence that black holes in anti-de Sitter spacetime are also unstable. The endstate may involve a violation of cosmic censorship. It would be of great interest to check all of these claims using numerical relativity.

## The purpose of these tables is to maintain a schedule of scientific talks and discussions relevant to your program.

## Go to current week.⬇

Week1TimePlace*SpeakerTitleComments, Links,...HolidayMartin Luther King, Jr. DayMartin HellerStrong coupling isotropization simplifiedMarco PaneroThe planar limit of strongly coupled gauge theories in 3+1 and in 2+1 dimensions2:00pm

2514

moderator: Ed Shuryakmoderator: Hans BantilanDiscussion: QCD with many flavors NfDiscussion: on Finding a Gravity Description of Heavy Ion CollisionsWeek 2TimePlace*SpeakerTitleComments, Links,...Vladimir FalkoOverview of the Physics of Graphene programcoordinatorset al.Organizational Meetingmoderators: David Berenstein, Larry YaffeDiscussion: why are we here? Open problems and what we would like to know and calculateNabil IqbalRomuald JanikJan 26

Paul Chesleram

Daniel NogradiIntroduction by George FlemingSo MatsuuraTimePlace*SpeakerTitleComments, Links,...Philippe de ForcrandToby WisemanHerbert NeubergerNon-analyticity in scale in the planar limit of QCDFrans PretoriusA new numerical approach to evolution of 5D asymptotically AdS spacetimesDavid GarfinkleSimon CatterallTwisted lattice supersymmetry: a status reportAsato TsuchiyaExpanding (3+1)-dimensional universe from a matrix model for superstringsPaul CheslerLiza HuijseThe power of supersymmetry in a lattice model for strongly interacting fermionsMithat Unsalmoderator: Hans BantilanDiscussion: strengths/weaknesses of current approaches on the lattice and gravityGary HorowitzInstability of anti-de Sitter SpacetimeWeek 4TimePlace*SpeakerTitleComments,LinksJun NishimuraDiscussion: (related to Tsuchiya's talk last week)(3+1)d spacetime from matrix modelsEdward ShuryakSounds of the Little Bang thermalization and jet quenchingHajime AokiHow Standard Model can appear from the matrix modelAnna HasenfratzStrongly coupled conformal systems with fundamental fermionsJoshua CoopermanQuantizing Horava-Lifshitz Gravity viaCausal Dynamical TriangulationsWeek 5TimePlace*SpeakerTitleComments,LinksFeb 14

Jacek WosiekMike TeperFeb 16

am

Moderators: Piotr Bizon, Frans PretoriusMasanori HanadaWeek 6TimePlace*SpeakerTitleComments,LinksJorge SantosMichael BuchoffRichard BrowerOleg AndreevWeek 7TimePlace*SpeakerTitleComments,LinksPau FiguerasModerator: Carsten GundlachIbrahima BahJoao PenedonesVolker BraunWeek 8TimePlace*SpeakerTitleComments,LinksDavid BerensteinTom AppelquistIssaku Kanamori*Aud=Auditorium, SSR=Small Seminar Room, MSR=Main Seminar Room, FR=Founders' Room, PL=Porthole LoungeAbstracts for focus week:Philippe de Forcrand(ETH Zurich, CERN, YITP)Simulating lattice QCD at finite baryon density

At non-zero baryon density, simulations of lattice QCD face a "sign problem" which prevents significant progress. In particular, the phase diagram of QCD as a function of temperature and chemical potential remains largely unknown. I recall the nature of the sign problem, the approaches used to circumvent it at small density, and point to a possible direction for progress.

Herbert Neuberger (Rutgers)Non-analyticity in scale in the planar limit of QCD

Using methods of numerical Lattice Gauge Theory we show that in the limit of a large number of colors, properly regularized Wilson loops have an eigenvalue distribution which changes non-analytically as the overall size of the loop is increased. This establishes a large-$N$ phase transition in continuum planar gauge theory, a fact whose precise implications remain to be worked out.

Frans Pretorius (Princeton)A new numerical approach to evolution of 5D asymptotically AdS spacetimes

I will describe a new numerical effort to solve Einstein gravity in 5-dimensional asymptotically Anti de Sitter spacetimes. The motivation is the gauge/gravity duality of string theory, with eventual application to scenarios (for example heavy ion collisions) that on the gravity side are described by dynamical, strong-field solutions. As a first step towards modeling such phenomena, we initially focus on spacetimes with SO(3) symmetry in the bulk; i.e., axisymmetric gravity, dual to plasma dynamics on the boundary with spherical or special conformal symmetry. As a test application we explore quasi-normal ringdown of highly deformed black holes in the bulk, and examine the degree to which the expectation value of the dual boundary stress tensor agrees with that of a conformal fluid.

David Garfinkle(Oakland)Novel(?) numerical methods for AdS gravitational collapse

It is to be expected that new numerical methods will be needed to do simulations of gravitational collapse in 5 dimensions and with AdS boundary conditions. Nonetheless, it is helpful to see how far we can get using the sort of methods that have worked for GR in 4 dimensions. This talk will presents results for spherically symmetric gravitational collapse of a scalar field in AdS 5 in both global and Poincare coordinates.

Simon Catterall(Syracuse)Twisted lattice supersymmetry: a status report

I will briefly review the construction of lattice Yang Mills theories which exhibit invariance under one or more twisted supersymmetries at non zero lattice spacing focusing in particular on a lattice model which targets N=4 YM in the naive continuum limit. I will show that the structure of the lattice model is remarkably similar to its continuum counterpart; the moduli space is not lifted to all orders in perturbation theory and the one loop beta function vanishes. I will then describe how the model may be simulated using standard Monte Carlo techniques borrowed from lattice QCD and hence how lattice studies can be used to probe the non perturbative structure of the theory and test aspects of the AdS/CFT correspondence.

Asato Tsuchiya(Shizuoka)Expanding (3+1)-dimensional universe from a matrix model for superstrings

We reconsider the matrix model formulation of type IIB superstring theory in (9+1)-dimensional space-time. Unlike the previous works in which the Wick rotation was used to make the model well-defined, we regularize

the Lorentzian model by introducing infrared cutoffs in both the spatial and temporal directions. Monte Carlo studies reveal that the two cutoffs can be removed in the large-N limit and that the theory thus obtained has no parameters

other than one scale parameter. Moreover, we find that three out of nine spatial directions start to expand at some "critical time", after which the space has SO(3) symmetry instead of SO(9).

Paul Chesler(MIT)Dynamical Hawking radiation and holographic thermalization

Holography provides a powerful tool to study non-equilibrium dynamics in strongly coupled quantum field theories, mapping challenging D dimensional quantum dynamics on to semi-classical gravity in D+1 dimensions. One interesting quantum field theory process to study is the creation and thermalization of a D = 4 strongly coupled quark-gluon plasma. Heavy ion collisions at RHIC and the LHC suggest that quark-gluon plasma can be created and thermalize in a time as short as 1 fm/c, the time it takes for light to traverse the diameter of a proton. Understanding the dynamics responsible for such rapid thermalization is a challenge using traditional perturbative field theory. Via holography, the creation of a quark-gluon plasma maps into the process of gravitational collapse and black brane formation. The thermalization of the quark-gluon plasma maps into the relaxation of the black brane geometry and thermalization of its Hawking radiation. I will describe new techniques for studying holographic thermalization and present results for thermalization times and mechanisms.

Liza Huijse (Harvard)The power of supersymmetry in a lattice model for strongly interacting fermions

We consider a class of models for strongly interacting fermions that possesses supersymmetry. The benefit of incorporating this property turns out to be twofold. First, the supersymmetry leads to a considerable degree of analytic control, allowing the rigorous derivation of quite a few results, in particular on quantum ground states. Second, it induces a subtle interplay between kinetic and potential terms, which gives rise to various interesting features, such as quantum criticality and superfrustration, characterized by an extensive ground state entropy. In this talk, I will give an overview of the main results for this system, while discussing the key techniques that are available due to supersymmetry.

Mithat Unsal(Stanford)Gauge dynamics and new instanton, bion and renormalon effects

I discuss the dynamics of four dimensional gauge theories with adjoint fermions for general gauge groups, both in perturbation theory and non-perturbatively, by using circle compactification with periodic boundary conditions for the fermions. There are new gauge phenomena, and new instanton effects. I will describe whether we can actually make sense of gauge theory in continuum. In compactified theory, I will give evidence that the elusive IR renormalons (for which no semi-classical configuration is known) of 't Hooft may have a semi-classical incarnation.

This is a molecule that Argyres and I refer to as "neutral bion". It carries zero topological charge and zero magnetic charge, and it corresponds to a pole in the Borel plane much closer to origin (by a factor of N) than the 4d instanton-anti-instanton pole. We recently derived this class of molecules by generalizing an old work of Bogomolny and Zinn-Justin from quantum mechanics to quantum field theory. I suspect we may have a chance to understand this theory in continuum.

Gary Horowitz (UCSB)Instability of anti-de Sitter Spacetime

I will describe recent evidence that anti-de Sitter spacetime is nonlinearly unstable. Generic small but finite perturbations eventually form small black holes. There are special solutions, called geons, which remain nonsingular and do not collapse. I will also describe (weaker) evidence that black holes in anti-de Sitter spacetime are also unstable. The endstate may involve a violation of cosmic censorship. It would be of great interest to check all of these claims using numerical relativity.

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