University of Crete HEP Seminars Spring 2012

### Parity-Violating Hydrodynamics in 2+1 Dimensions

 Speaker: Rene Meyer Department: University of Crete Slides: [PDF] Time: Friday 17 February 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: We study relativistic hydrodynamics of normal fluids in two spatial dimensions. When the microscopic theory breaks parity, extra transport coefficients appear in the hydrodynamic regime, including the Hall viscosity and the anomalous Hall conductivity. I present a classification of all these transport coefficients in first order hydrodynamics. All the parity-breaking transport coefficients turn out to be dissipationless, and some of them are related to the thermodynamic response to an external magnetic field and to vorticity. In addition, I give a holographic example of a strongly interacting relativistic fluid where the parity-violating transport coefficients are computable.

### Holographic Wilson Loops and Topological Insulators

 Speaker: Andy O'Bannon Department: Cambridge U., DAMTP Slides: [PDF] Time: Tuesday 21 February 2012 at 15:15 Venue: The 2nd floor seminar room of the physics department Abstract: Topological Insulators (TI's) are materials characterized by gapless edge states producing quantized, dissipationless transport. In more formal terms, they are defined as insulating materials characterized by a topological quantum number distinct from the vacuum. They thus fall outside the Landau-Ginzburg paradigm in which materials are classified by symmetry-breaking order parameters. Examples of TI's include quantum Hall systems, for which the topological quantum number is an integer (the quantized Hall conductivity), and recently-discovered materials for which the topological quantum number is Z2-valued. These systems all admit effective descriptions in terms of non-interacting electrons. Indeed, a complete classification now exists of all possible TI's described by non-interacting electrons. An open question is what kinds of TI states are possible in the presence of interactions. Gauge-gravity duality, or holography, gives us access to strongly-interacting systems, including some special TI's. In this talk I will describe one example a "holographic topological insulator," and compare the potential that a test charge feels in the presence of that TI, as computed from Wilson loops, to the result for real TI's.

### Poor man's holography: How far can it go?

 Speaker: Hong Bao Zhang Department: University of Crete Time: Tuesday 28 February 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: General relativity tells us gravity is geometry. But this is not the end of the story for many reasons. In particular, gravity may be identified as sort of holographic object at the end of day. In this talk, I will report our ongoing work towards that goal. To be more precise, I will show that within the context of general relativity various kinds of entropy production on the boundary correspond exactly to the horizon area increase of black hole in the bulk. The result obtained is fantastically generic in the sense that it does not require the spacetime in question to be asymptotically AdS, or the boundary to be conformal boundary, and so on, so forth.

### The Hilbert Series of SQCD

 Speaker: Matti Järvinen Department: University of Crete Slides: [PDF] Time: Friday 2 March 2012 at 13:15 Venue: The 2nd floor seminar room of the physics department Abstract: After an introduction to Hilbert series, I discuss my recent work (arXiv:1112.5454) on the Hilbert series of N=1 supersymmetric QCD with U(N_c) and SU(N_c) color symmetry. I use two methods to compute the series, which have previously been applied to similar computational problems in the analysis of decay of unstable D-branes: expansions using Schur polynomials, and the log-gas approach related to random matrix theory.

### From N=4 Super Yang-Mills to SuperConformal QCD: Spin Chains and Holography

 Speaker: Elli Pomoni Department: Humboldt University Slides: [PDF] Time: Tuesday 6 March 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: N = 2 Super Conformal 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 concentrate on 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.

### Holographic dynamics of the chiral condensate and vector-axial vector correlator in weak electric field

 Speaker: Ioannis Iatrakis Department: University of Crete Time: Friday 9 March 2012 at 13:15 Venue: The 2nd floor seminar room of the physics department Abstract: The study of the transverse part of the vector-axial vector flavor current correlator in the presence of weak external electric field is presented. The correlator is calculated using a bottom-up AdS/QCD model, that includes both contributions of higher string states and the non-linear dynamics of the chiral condensate. It is shown that for low momenta the result agrees with the relation proposed by Son and Yamamoto motivated by a simpler holographic model. This suggests that the Son-Yamamoto relation is generically valid in the IR of models with the proper chiral symmetry breaking pattern.

### Informal Seminar: Chiral magnetic effect

 Speaker: Andy O'Bannon Department: Cambridge U., DAMTP Time: Tuesday 13 March 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: TBA

### Z_N Potential for black brane on a Circle

 Speaker: Takeshi Morita Department: University of Crete Time: Friday 16 March 2012 at 13:15 Venue: The 2nd floor seminar room of the physics department Abstract: We consider an Euclidian black Dp brane localized on an S^1 circle and take a near horizon limit by keeping the radius of the circle finite. We find that a potential for the center mass of the brane along the S^1 direction appears and this potential breaks the continuum translation symmetry along the S^1 direction to a discrete Z_N symmetry where N is the charge of the brane. Thus the position of the brane is restricted to the discrete values in low energy. This phenomenon is related to the fact that the dual gauge theory is SU(N) rather than U(N). This would be important in the study of the Gregory-Laflamme transition in holography. We also discuss an application to holographic QCD in the D4 brane model.

### A `double cover' for the SO(6)xSO(2) symmetric sector of N=8 gauged supergravity in four dimensions

 Speaker: Ioannis Papadimitriou Department: Instituto de Fisica Teorica (IFT UAM/CSIC) Time: Friday 23 March 2012 at 13:15 Venue: The 2nd floor seminar room of the physics department Abstract: It known that the SO(6)xSO(2) symmetric one-scalar consistent truncation of N=8 gauged supergravity in four dimensions is related via a field redefinition to a conformally coupled scalar coupled to Einstein-Hilbert gravity and with a simple quartic self interaction. However, only a subset of the solutions in the conformally coupled frame can be translated to solutions in the minimally coupled frame, since for certain solutions the aforementioned field redefinition becomes singular. I will present a novel Z_2 on-shell symmetry of this system in the conformally coupled frame, corresponding to a duality between the cosmological constant and the quartic coupling, and I will argue that this symmetry leads to a doubling of the solution space. The quotient of the solution space in the conformally coupled frame by this Z_2 symmetry can then be identified with the solution space in the minimally coupled frame, thus establishing the equivalence between the two descriptions of this sector of N=8 gauged supergravity in four dimensions.

### Hydrodynamics and the entropy current

 Speaker: Amos Yarom Department: Technion Slides: [PDF] Time: Tuesday 27 March 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: I'll discuss the role of an entropy current in constraining the equations of motion of relativistic hydrodynamics especially in theories in which parity is violated. After giving a few holographic examples of parity violating fluids I will discuss how one may obtain the same constraints on the equations of motion using equilibrium properties of the system.

### Superconfornal Index A Window on Seiberg Duality

 Speaker: Hugh Osborn Department: Cambridge University Slides: [PDF] Time: Thursday 29 March 2012 at 11:15 ( Time has been changed from the previous announcement!!) Venue: The ground floor room 1 (Aithousa 1) of the physics department ( Irregular location ) Abstract: The superconformal index can be determined using just the R charges and representations for a superconformal theories in four dimensions. For theories related by Seiberg duality the index for the different theories should be identical. The mathematical identities required have been proved in just the past few years and are very non trivial. The index identities may provide a new link between theoretical physics and some parts of pure mathematics.

### Spatially modulated phases in AdS/CFT

 Speaker: Aristomenis Donos Department: Imperial College Slides: [PDF] Time: Friday 30 March 2012 at 11:15 ( Time has been changed from the previous announcement!!) Venue: The 2nd floor seminar room of the physics department Abstract: The AdS/CFT correspondence is a powerful tool to analyse strongly coupled quantum field theories. Over the past few years there has been a surge of activity aimed at finding possible applications to condensed matter systems. One focus has been to holographically realise various kinds of phases via the construction of fascinating new classes of black hole solutions. In this framework, I will discuss the possibility of describing finite temperature phase transitions leading to spontaneous breaking of translational invariance of the dual field theory at strong coupling.

### Aspects of the a-Theorem

 Speaker: Adam Schwimmer Department: Weizmann Institute Slides: [PPT] Time: Monday 2 April 2012 at 11:15 (Irregular Date and Time) Venue: The 2nd floor seminar room of the physics department Abstract: The general proof of the a-Theorem using Trace Anomaly Matching will be discussed. An alternative argument for massive flows will be outlined and compared with the general proof.

### Results from the first heavy ion run with the ALICE experiment at the CERN LHC

 Speaker: Yiota Foka Department: GSI Slides: [PPT] Time: Tuesday 3 April 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: After almost two decades of preparation ALICE, the dedicated heavy ion experiment at the CERN LHC, took first data with proton collisions at the end of 2009 and with lead beams at the end of 2010 at a cetre-of-mass energy of 2.76 TeV/nucleon. An overview of the ALICE results from the first Pb-Pb run is presented.

### Results from the first heavy ion run with the ALICE experiment at the CERN LHC (continued)

 Speaker: Yiota Foka Department: GSI Time: Wednesday 4 April 2012 at 15:15 Venue: The 3rd floor seminar room of the physics department Abstract: After almost two decades of preparation ALICE, the dedicated heavy ion experiment at the CERN LHC, took first data with proton collisions at the end of 2009 and with lead beams at the end of 2010 at a cetre-of-mass energy of 2.76 TeV/nucleon. An overview of the ALICE results from the first Pb-Pb run is presented.

### All-loop S-matrix of planar N=4 SYM from Yangian symmetry

 Speaker: Song He Department: MPI in Postdam Slides: [PDF] Time: Tuesday 24 April 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: We derive a set of equations obeyed by the S-matrix of planar N=4 SYM. The equations render the S-matrix invariant under a suitably defined Yangian symmetry, and determine it at any value of the coupling. When expanded in powers of the coupling, they give derivatives of amplitudes as single integrals over lower-loop ones. We apply them on a few examples, deriving a recent result on the two-loop NMHV and fixing previously unknown coefficients in a recent Ansatz for the three-loop MHV amplitudes.

### Two applications of holography

 Speaker: Umut Gürsoy Department: CERN Slides: [PDF] Time: Wednesday 2 May 2012 at 15:15 Venue: The 3rd floor seminar room of the physics department Abstract: I will review two new developments in applied AdS/CFT correspondence. The first application is concerned with the thermodynamics of the quark-gluon plasma. In particular, I will explain how the holographic description of the thermodynamics of SU(N) gauge theories can explain a universal behavior observed in the interaction measure $T^\mu_\mu$ as a function of temperature, in 3+1 and 2+1 dimensions. The second development is about how to holographically describe physics of elementary fermionic excitations in cold atom systems.

### Department Colloquium: "Little Bang at Big Collider: Results with heavy ions from the LHC"

 Speaker: Jürgen Schukraft Department: CERN Time: Thursday 3 May 2012 at 17:15 Venue: The 3rd floor seminar room of the physics department Abstract: At the end of 2010, the CERN Large Hadron Collider started operation with heavy ion beams, Lead on Lead at a centre-of-mass energy of 2.76 TeV/nucleon, opening a new era in ultra-relativistic heavy ion physics at energies exceeding previous accelerators by more than an order of magnitude. This talk summarizes the results from the first year of ion physics at the LHC obtained by the three experiments participating in the ion program, i.e. ALICE, ATLAS, and CMS; comparing them where appropriate with data from lower energies (RHIC and SPS), and focusing on areas where significant progress has been made in the study of hot and dense matter, the Quark Gluon Plasma.

### Self-tuning and the cosmological constant problem

 Speaker: Christos Charmousis Department: Univ. Paris-Sud Slides: [PDF] Time: Monday 7 May 2012 at 15:15 Venue: The 3rd floor seminar room of the physics department Abstract: We will discuss the cosmological constant problem in the context of self-tuning scalar tensor theories in 4 dimensions: can a scalar self-tune to an abruptly changing cosmological constant without affecting the spacetime metric? After reviewing the most general scalar tensor theory proposed in the 70 's by Hornedski we shall define and then apply the self-tuning filter. The self tuning theory will be a scalar tensor theory dubbed fab 4. We shall briefly discuss some of its geometric and other properties.

### Surprising properties of certain strongly coupled CFTs in black hole backgrounds

 Speaker: Toby Wiseman Department: Imperial College Time: Tuesday 8 May 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: QFT in fixed curved spacetime is a fascinating subject. This is particularly true for black hole spacetimes, such as Schwarzschild where one expects to see Hawking radiation. In free or weakly coupled QFT one can compute this explicitly. In this talk I will describe how AdS-CFT allows us new tools to compute results for certain strongly coupled CFTs. Such calculations require that we construct a specific (and rather exotic) black hole solving 5-d Einstein equations with a negative cosmological constant. I will very briefly describe how new numerical techniques allow this to be done, and will show a solution that, via AdS-CFT, describes certain strongly coupled CFTs on a fixed Schwarzschild background. Interestingly we shall see that in this case, the expectation gained from the free field intuition completely fails to describe these strongly coupled results, where in fact Hawking radiation is hugely suppressed. This is closely related to the existence of black holes on Randall-Sundrum branes which I will also discuss and show results for.

### Einstein-(Maxwell)-Dilaton theories: generalised dimensional reduction and holographic applications

 Speaker: Blaise Goutéraux Department: APC, Paris Slides: [PDF] Time: Thursday 10 May at 15:15 Venue: The 2nd floor seminar room of the physics department Abstract: Einstein-Maxwell-Dilaton theories have recently attracted a lot of attention in holography. In this talk, I will explain how they may derive from scale invariant theories using generalised dimensional reduction, where the number of reduced dimensions is traded against a real, analytically continued parameter. This technique allows to generate easily new black hole solutions (or recover know ones) in gravity plus scalars theories, explains their scaling properties, as well as facilitates the computation of holographic observables such as the shear viscosity and other transport coefficients.

### Probes in plasmas with unquenched quarks

 Speaker: Liuba Mazzanti Department: Santiago de Compostela U. Slides: [PDF] Time: Tuesday 15 May 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: We analyze the holographic gravity model dual to a quark-gluon plasma with massless dynamical quarks in the Veneziano limit. The background of smeared D7 branes in a D3 near horizon geometry is reviewed. On top of this we add probe D7 branes to produce results for phenomenologically relevant quantities such as the meson melting phase transition point, the screening length, the drag force and diffusion constants for a heavy quark.

### Seiberg dualities and the 3d/4d connection

 Speaker: Vasilis Niarchos Department: Crete U. Time: Tuesday 22 May 2012 at 14:15 Venue: The 2nd floor seminar room of the physics department Abstract: I will discuss recent work on the mathematics of a 3d/4d connection that relates Seiberg duality for d=4 N=1 SQCD theory to Aharony/Giveon-Kutasov dualities for d=3 N=2 SQCD theories.