Workshop Programme
for period 20  24 August 2007
Exploring QCD: Deconfinement, Extreme Environments and Holography
20  24 August 2007
Timetable
Monday 20 August  
09:5510:00  Welcome  Simon Hands  
10:0011:00  Shuryak, E (Stony Brook)  
Understanding the strongly coupled QuarkGluon plasma  Sem 1  
The talk is a review of the current status of the field, which is very much in flux. Two central topics will be: (i) applications of AdS/CFT (both static finite T and dynamical) and (ii) electricmagnetic duality and the role of magnetic objects in sQGP. 

11:0011:30  Coffee  
11:3012:30  Schaefer, T (North Carolina)  
QCD and dense baryonic matter: an introduction  Sem 1  
We provide an overview of our present knowledge of the phase diagram of cold and dense baryonic matter. We consider, in particular, two regimes in which systematic field theory calculations are possible: The regime of very low baryon density which can be studied using effective field theory methods, and the regime of very high baryon density in which weak coupling QCD is applicable. 

12:3013:30  Lunch at Wolfson Court  
14:0015:00  Aharony, O (Weizmann)  
String theory and holographic descriptions for large N gauge theories  where do we stand?  Sem 1  
I will review what is known about string theoretic and holographic dual descriptions of large N gauge theories, focusing on the progress towards a description of large N QCD. 

15:0015:30  Tea  
15:3016:30  Rajagopal, K (MIT)  
Probing the properties of QuarkGluon plasma  Sem 1  
16:3017:30  Nair, V (CUNY)  
The Hamiltonian approach to YangMills (2+1): basics and update  Sem 1  
YangMills theories in 2+1 (or 3) dimensions are interesting as nontrivial gauge theories in their own right and as effective theories of QCd at high temperatures. By a suitable parametrization of fields and techniques from 2dimensional CFT, a Hamiltonian approach has been developed which has led to interetsing results on the vacuum wave function, string tension, mass gap, etc. I shall review the basics of this approach, emphasizing symmetries and robustness of results, and also provide a short update on its status. 

17:3018:30  Welcome Wine Reception 
Tuesday 21 August  
09:0010:00  Fodor, Z (Wuppertal)  
Lattice QCD thermodynamics at mu=0 and mu$>$0  Sem 1  
Recent results of lattice thermodynamics will be presented. The nature of the transition, the absolute scale of the transition, the static potential, the equation of state and the phase diagram will be discussed. The analyses used a.) physical quark masses and b.) controlled continuum extrapolations. 

10:0011:00  de Forcrand, P (ETH)  
Finite density QCD on the lattice  Sem 1  
11:0011:30  Coffee  
11:3011:50  Megias, E (Brookhaven National Laboratory)  
Polyakov loop effects in QCD and chiral quark models  Sem 1  
We discuss the importance of the inclusion of the Polyakov loop in computation of observables in QCD at finite temperature. In the deconfinement phase it is possible to obtain a fully gauge invariant effective action of QCD, which means invariance under large gauge symmetries, and it is necessary to consider the Polyakov loop. In the confinement phase of QCD, traditional Chiral Quark Models become inconsistent with Chiral Perturbation Theory at finite temperature, they predict deconfinement even at low temperature, etc. These problems can be solved if we consider the coupling of the Polyakov loop in these models. In particular, the PolyakovNJL model predicts a phase transition which agrees very well with lattice data, if we consider a convenient nonperturbative parametrization for the distribution of the Polyakov loop in pure gluodynamics. The main theoretical justification of PolyakovChiral Quark Models is large gauge invariance. Some references are: E. Megias, E. Ruiz Arriola and L.L. Salcedo PLB563:173178(2003), PRD69:116003(2004), PRD74:065005(2006), PRD74:114014(2006), JHEP0601:073(2006), PRD75:105019(2007). Related Links


11:5012:10  Furui, S (Teikyo)  
Infrared features of finite temperature lattice Landau gauge and Coulomb gauge QCD  Sem 1  
Color diagonal and color antisymmetric ghost propagator of zero temperature and finite temperature configurations of the MILC collaboration are measured after Landau gauge fixing and the color confinement mechanism and their temperature dependence are discussed. Temperature dependence of the transverse, electric and magnetic gluon propagator, the screening mass, the A^2 condensate and the ghost condensate are also measured and by comparing the results of quenched configurations and unquenched configurations, effects of quarks on the ghost propagator, which is an essential ingredient of the confinement, is discussed. Comparison of the Landau gauge and the Coulomb gauge QCD is also given. (heplat/0612009) Related Links


12:1012:30  Akemann, G (Brunel)  
F\_pi from individual Dirac eigenvalues at nonzero mu  Sem 1  
In the epsilonregime of lattice QCD one can get an accurate measurement of the pion decay constant by monitoring how just one single Dirac operator eigenvalue behaves when subjected to different external vector sources. This can be done both for imaginary isospin chemical potential with real eigenvalues, as well as for real chemical potential with complex eigenvalues. We briefly sketch the formalism how to compute individual Dirac eigenvalue distributions from Random Matrix Theory and compare to Lattice data. 

12:3013:30  Lunch at Wolfson Court  
14:0014:30  Aarts, G (Swansea)  
Spectral functions and transport from the lattice  Sem 1  
In lattice QCD, the Maximum Entropy Method can be used to reconstruct spectral functions from euclidean correlators obtained in numerical simulations. We show that at finite temperature the most commonly used algorithm, employing Bryan's method, is inherently unstable at small energies and give a modification that avoids this. We demonstrate this approach using the vector currentcurrent correlator obtained in quenched QCD at finite temperature. Our first results indicate a small electrical conductivity above the deconfinement transition. 

14:3015:00  Lombardo, MP (INFNLNF)  
Glueball spectrum and screening properties across the superfluid transition of two colour QCD  Sem 1  
QCD with two color undergoes a transition to a phase with diquark condensate when the quark chemical potential equals half the pion mass. We investigate the gluonic properties of this transition by inspecting the behaviour of the glueball correlators. It turns out that the glueball masses change very little at the transition, supporting the view that the suprfluid transition is not deconfining, while the amplitude of the propagators drops, suggesting a strong reduction of the gluon condensate. 

15:0015:30  Tea  
15:3016:10  Rebhan, A (Technical University Vienna)  
Nonabelian plasma instabilities  Sem 1  
Quarkgluon matter as produced in the early stages of an ultrarelativistic heavyion collison has strong momentum space anisotropies. Even at arbitrarily weak coupling this leads to nonperturbative phenomena in the form of nonabelian plasma instabilities. Their dynamics will be discussed within the framework of the hardloop effective theory, both for a stationary anisotropic plasma and an anisotropically expanding one. 

16:1016:50  Petreczky, P (Brookhaven National Laboratory)  
Heavy quarks at finite temperature  Sem 1  
I am going to discuss how heavy quarks could be used as probes of the deconfined strongly interacting matter. First I will discuss correlation functions of infinitely heavy (static) quarks and color screening calculated on the lattice. Then I show recent results on quarkonia correlators and spectral functions calculated on the lattice and in potential models. The transport contribution to the quarkonium will be also discussed. 

16:5017:30  Hong, DK (Pusan National University)  
Baryons in AdS/QCD  Sem 1  
We construct a holographic model for baryons in the context of AdS/QCD and study the spin1/2 and spi3/2 nucleon spectra and its couplings to mesons, taking fully account of the effects from the chiral symmetry breaking. A pair of 5D spinors is introduced to represent both left and right chiralities. Our model contains two adjustable parameters, the infrared cutoff and the Yukawa coupling of bulk spinors to bulk scalars, corresponding to the order parameter of chiral symmetry. Taking the lowestlying nucleon mass as an input, we calculate the mass spectrum of excited nucleons and the nucleon couplings to pions. The excited nucleons show a paritydoubling pattern with smaller pionnucleon couplings. 

18:4519:30  Dinner at Wolfson Court (Residents only) 
Wednesday 22 August  
09:0009:40  Johnson, C (USC)  
Phase structure of strong flavour dynamics  Sem 1  
This is a report on recent work on the dynamics of strongly coupled gauge theory with quenched flavours, studied using D7brane probes of various string theory duals. 

09:4010:20  Erdmenger, J (WernerHeisenbergInstitut)  
Adding flavour to holographic duals of finite temperature field theories  Sem 1  
We review recent work on adding flavour to strongly coupled finite temperature field theories by embedding D7 brane probes into the AdSScharzschild black hole background.In particular, transport processes in the presence of an isospin chemical potential are examined. We also discuss the behaviour of mesons in this scenario. 

10:2011:00  Kiritsis, E (Crete)  
Exploring improved holographic models for QCD  Sem 1  
Various holographic approaches to QCD in five dimensions are explored using input both from the putative noncritical string theory as well as QCD. It is argued that a gravity theory in five dimensions coupled to a dilaton and an axion may capture the important qualitative features of pure QCD. A part of the higher $\alpha'$corrections are resumed into a dilaton potential. The potential is shown to be in onetoone correspondence with the exact $\beta$function of QCD, and its knowledge determines the full structure of the vacuum solution. The geometry near the UV boundary is that of AdS$_5$ with logarithmic corrections reflecting the asymptotic freedom of QCD. We find that all relevant confining backgrounds have an IR singularity of the ``good" kind that allows unambiguous spectrum computations. Near the singularity the 't Hooft coupling is driven to infinity. Asymptotically linear glueball masses can also be achieved. The classification of all confining asymptotics, the associated glueball spectra and meson dynamics are also addressed. 

11:0011:30  Coffee  
11:3011:50  Meyer, HB (Massachusetts Institute of Technology)  
A calculation of the shear and bulk viscosities of gluodynamics  Sem 1  
We present an accurate lattice calculation of the Euclidean twopoint functions of the energymomentum tensor in the SU(3) gauge theory at temperatures relevant to present and future heavy ion colliders. This allows us to give a robust upper bound on the shear and bulk viscosities. We compare the correlators to AdS/CFT predictions and quantify the deviations from conformality. Finally, we describe the extraction of the corresponding spectral functions and give our best estimates of the transport coefficients. Related Links


11:5012:10  Zhitnitsky, A (UBC)  
Charge separation phenomenon in Big Bang and Little Bang (RHIC) during the QCD phase transistion  Sem 1  
We discuss a novel the "charge separation phenomena " which may happen during the QCD phase transition. This effect is due to the anomalous terms in the effective lagrangian in the presence of nonzero chemical potential and the socalled theta term. There is a number of cosmological/astrophysical observations (such as similarity of dark matter and baryon densities in universe) supporting this picture. There are also preliminary results from RHIC which also apparently demonstrate that the separation of charges takes place if some conditions are met. 

12:1012:30  Ramos, RO (Rio de Janeiro)  
Thermodynamics of the 2+1D GrossNeveu model beyond large N approximation  Sem 1  
A complete thermodynamics analysis for the 2+1D GrossNeveu model is performed using the optimized perturbation method (or linear delta expansion). Analytical results for all critical quantities, like the critical temperature and chemical potential for (discrete) phase transition are obtained. The first order phase transition line and tricritical point, not seen from the available results for the model using for example the standard largeN approximations, are obtained. Our results for the phase diagram for the model also indicates the presence of a "liquidgas" phase, not previously seen from other methods used to analyze the model. Related Links


12:3013:30  Lunch at Wolfson Court  
14:0014:20  GarciaGarcia, AM (Princeton)  
Phase transitions in QCD as metalinsulator transitions  Sem 1  
We investigate in what situations the phenomenon of Anderson localization, originally introduced in condensed matter, may be relevant in the context of QCD. At the chiral phase transition we provide compelling evidence from lattice and phenomenological instanton liquid models that the QCD Dirac operator undergoes a metal  insulator transition similar to the one observed in a disordered conductor. This suggests that Anderson localization plays a fundamental role in the chiral phase transition. Based on a recent relation between the Polyakov loop and the spectral properties of the Dirac operator we discuss how the confinementdeconfinement transition may be related to a metalinsulator transition in the bulk of the spectrum of the Dirac operator. 

14:2014:40  Nakaggawa, H (Nara)  
Phase structure of thermal QCD based on the hard thermal loop improved Ladder DysonSchwinger equation  Sem 1  
Analyses of the DysonSchwinger equation (DSE) have proven to be successful in studying the phase structure of vacuum gauge theories. In the Landau gauge DSE with the ladder kernel for the fermion mass function in the vacuum QED, the fermion wave function renormalization constant is guaranteed to be unity, satisfying the Ward identity. Thus irrespective of the problem of the ladder approximation, the results obtained would be gauge invariant Although in the vacuum case, despite the use of ladder kernel, in the analysis in the Landau gauge the Ward identity is guaranteed to be satisfied, at finite temperature/density there is no such guarantee. In fact, even in the Landau gauge the fermion wave function renormalization constant largely deviates from unity, being not even real. In finite temperature/density QCD/QED, the results obtained from the ladder DysonSchwinger equation explicitly violate the Ward identity, thus depend on the gauge, their physical meaning being obscure. In this paper, we study, in the analysis of the HTL resummed improved ladder DS equation for the fermion mass function in thermal QCD, the procedure how we can get the "gauge invariant" solution in the sense it satisfies the Ward identity. The proposed procedure works excellently to obtain a "gauge invariant" solution, at least in the numerical analysis. To get such a solution it is essential that the gauge parameter ? depends on the momentum of the gauge boson. Properties of the "gaugeinvariant" solutions are discussed. A theoretical investigation is now underway. 

14:4015:00  Jarvinen, M (Helsinki)  
Perturbative gauge theory in a background  Sem 1  
Motivated by the gluon condensate in QCD I study Abelian gauge theory in the presence of a constant (p=0) gluon background. The background adds an extra \sim \mu^2\delta^4(p) term to the free (Abelian) gluon propagator. I show how to evaluate dressed Green functions at tree level in the coupling \alpha, but summed to all orders in the parameter \mu characterizing the background field. Instead of a pole at p^2=m^2, the dressed quark propagator has a discontinuity that vanishes exponentially for large p^2. For vanishing quark mass I study a propagator solution which breaks chiral symmetry spontaneously. Related Links 

15:0015:30  Tea  
15:3016:10  Laine, M (Bielefeld)  
Realtime static potential and quarkonium spectral function in hot QCD  Sem 1  
The spectral function of heavy quarkonium is an observable possessing both a theoretically transparent connection to heavy ion phenomenology, and a nontrivial qualitative change as a function of the temperature, making it a conceptually clean probe of deconfined QCD matter. I review some basic facts concerning this observable, and discuss then recent progress on its determination, by approaching the physically relevant temperature range from the hightemperature side, where the spectral function can be computed systematically in (resummed) weakcoupling expansion. 

16:1016:30  Kimura, D (Hiroshima)  
NJL model at finite temperature and chemical potential in dimensional regularization  Sem 1  
We study the twoflavors NambuJonaLasinio (NJL) model at finite temperature and chemical potential by using the dimensional regularization. Since this model is nonrenormalizable in four spacetime dimensions, physical results depend on the regularization method. We also discuss the color superconductivity in the extended NJL model by using the dimensional regularization. 

18:4519:30  Dinner at Wolfson Court (Residents only) 
Thursday 23 August  
09:0009:40  Stephanov, M (Illinois)  
Holographic QCD  Sem 1  
I shall describe a bottomup approach to constructing a holographic dual to QCD: AdS/QCD. Holographic models simultaneously satisfy chiral symmetry constraints, QCD sum rules and match asymptotic behavior of QCD correlation functions. The simplest model of this type gives a remarkably good fit to low energy hadronic observables. 

09:4010:20  de Teramond, G (Costa Rica)  
AdS/CFT integrability and lightfront dynamics in a semiclassical approximation to QCD  Sem 1  
We derive lightfront equations for the bound states of massless quarks from the semiclassical approximation to the equations of motion describing the propagation of bosonic and fermionic modes on AdS space and the mapping of string modes to lightfront wavefunctions of hadrons in physical spacetime. The effective equations describing lightfront eigenmodes in 3+1 spacetime depend on the average impact distance between the constituents and possesses remarkable algebraic structures and integrability properties dictated by the conformality of the theory. The holographic model is extended to include a confining potential while preserving its algebraic structure. The gauge/gravity correspondence provides insights into inherently nonperturbative aspects of hadronic physics, such as the orbital and radial spectra and the behavior of form factors in the spacelike and the timelike regions. Related Links


10:2011:00  Sannino, F (NBI Copenhagen \& SDU Odense)  
The phase diagram of higher dimensional representations and alternative large N limits: from QCD to minimal walking theories  Sem 1  
I will present the phase diagram, as function of number of flavors and colors, for SU(N) gauge theories with matter in "any" irreducible representation of the gauge group. The talk will then be split into two parts: QCD applications: The introduction of higher dimensional representations will allow me to define new large N limits capturing properties of QCD at leading N which are poorly described in the 't Hooft one. New Strong Dynamics at the Electroweak Scale: The phase diagram will provide us with the first and most complete catalogue of strongly coupled theories near an infrared fixed point which can be used to break the Electroweak theory dynamically while not being at odds with precision measurements. Theories near an infrared fixed point have a coupling constant with a "walking" rather than a running dependence on the energy scale and hence are termed "walking" theories. Our phase diagram will allow me to define "Minimal Walking Theories" and their phenomenological consequence for the physics at LHC. 

11:0011:30  Coffee  
11:3012:30  Shifman, M (Minnesota)  
Highly excited mesons, linear regge trajectories and pattern of the chiral symmetry realisation  Sem 1  
We discuss the issue of the chiral symmetry restoration in high excitations. On the phenomenological side we use the linearity and equidistance of the quark meson Regge trajectories to show that the NambuGoldstone mode persists at high energies. This conclusion is supported by theoretical consideration within the framework of the SakaiSugamoto construction. 

12:3013:30  Lunch at Wolfson Court  
14:0014:20  Kojo, T (Kyoto)  
Peristaltic modes of single vortex in U(1) and SU(3) gauge theories  Sem 1  
Using the Abelian Higgs model, we study the radial excitations of single vortex and their propagation modes along the vortex line. We call such beyondstringy modes peristaltic modes of single vortex. With the profile of the static vortex, we derive the vortexinduced potential, i.e., singleparticle potential for the Higgs and the photon field fluctuations around the static vortex, and investigate the coherently propagating fluctuations which corresponds to the vibration of the vortex. We derive, analyze and numerically solve the field equations of the Higgs and the photon field fluctuations around the static vortex with various GinzburgLandau parameter kappa and topological charge n. Around the BPS value or critical coupling kappa^2=1/2, there appears a significant correlation between the Higgs and the photon field fluctuations mediated by the static vortex. As a result, for kappa^2=1/2, we find the characteristic newtype discrete pole of the peristaltic mode corresponding to the quasiboundstate of coherently fluctuating fields and the static vortex. We investigate its excitation energy, correlation energy of coherent fluctuations, spatial distributions, and the resulting magnetic flux behavior in detail. Our investigation covers not only usual TypeII vortices with n=1 but also TypeI and TypeII vortices with n no less than 1 for the application to various general systems where the vortexlike objects behave as the essential degrees of freedom. We also consider the peristaltic modes of dual string between quarks using the dual Higgs theory as the effective theory of low energy QCD. The implications for hadron physics will be discussed. Related Links 

14:2014:40  Hoyos, C (Swansea)  
Correlation lengths in strongly coupled plasmas from holography  Sem 1  
At high temperature, finite correlation lengths appear due to the stochastic nature of thermal fluctuations. Then, small timedependent perturbations localized in the plasma will not affect regions beyond that length. This can be shown as an exponential decay of the two point correlator with the distance. In N=4 we can study the plasma phase using the holographic gravity dual, a black hole in AdS_5. We identify correlation lengths of different operators with the imaginary part of complex momentum modes of the dual fields in the black hole geometry, and explore their dependence with frequency. 

14:4015:00  Sin, SJ (Hanyang)  
Bulk filling branes and gravity back reaction for finite baryon number density  Sem 1  
It has been believed that charged black hole is not relevant to the BARYON density. Here we suggest that it is relevant in the case where the brane is filling the whole AdS bulk: in high temperature, the background becomes RN$AdS$ black hole as a consequence of the gravity back reaction to the presence of charge. We show that the main difference of Rcharge and baryon charge lies on the strength of couplings to the gravity: the latter is suppressed by $N_f/N_c$ relative to the former. With such gravity back reaction, density dependence of physical quantities can be encoded in quadratic action of AdS/QCD without adding higher order $\alpha'$ correction. We discuss phase diagram based on this picture with flat boundary and show that the phase diagram closes at the finite density or chemical potential unlike the brane embedding approach without gravity back reaction. 

15:0015:30  Tea  
15:3016:10  Vuorinen, A (Technical University Vienna)  
Spinning dragging strings  Sem 1  
I will review a recent AdS/CFT computation of the drag force experienced by a heavy quark moving through strongly coupled N=4 SYM plasma at finite R charge density. I will explain, how a discrepancy between two previous calculations has now been resolved, and will briefly discuss the D7 brane boundary conditions relevant for the different classes of spinning string solutions found. 

16:1016:50  Starinets, AO (Perimeter Institute)  
Spectral functions and transport from holography  Sem 1  
I will review methods of computing spectral functions and transport coefficients from gauge/gravity duality. 

17:1017:30  Nicotri, S (Universita deglie Studi di Bari)  
Light glueballs in a holographic description of QCD  Sem 1  
We evaluate the spectra of light scalar and vector glueballs in a holographic model of QCD with a dilaton background field. In particular we study how the masses depend on the background and on the geometry of the bulk. 

19:3022:30  Conference Garden Party at Clare Hall 
Friday 24 August  
09:0010:00  Nastase, H (Tokyo Institute of Technology)  
High energy QCD collisions at RHIC and the LHC from dual black hole production  Sem 1  
I analyze the high energy collisions of hadrons in QCD from the point of view of gravity duals of QCD. Dual black hole formation dominates at least above 10 GeV, and the total QCD cross section behaviour with s is obtained. The saturation of the Froissart bound in QCD maps to production of black holes in the IR of the dual. These correspond to the RHIC fireballs and similar objects expected at the LHC. The temperature of the fireball is derived, as well as other properties. A simple field theory toy model shows how it is possible to obtain black holelike properties in QFT. The model has thermal horizons that trap information, and presents aparent information loss, which should be restored by unitarity. 

10:0010:20  Parnachev, A (Stony Brook)  
Comments on holographic QCD  Sem 1  
We study D4D8\bar D8 brane configuration which describes large N QCD in a certain regime of parameters. The high energy meson spectrum is computed analytically. We consider this system at finite chemical potential and temperature and find a line of first order phase transitions. 

10:2010:40  Braga, NRF (Rio de Janeiro)  
On a holographic model for confinement/deconfinement  Sem 1  
We study the thermodynamics of the hard wall model, which consists in the introduction of an infrared cutoff in asymptotically AdS spaces. This is a toy model for confining backgrounds in the context of the gauge/gravity correspondence. We use holographic renormalization and reproduce the existence of a Hawking Page phase transition recently discussed by Herzog. We also show that the entropy jumps from N^0 to N^2, which reinforces the interpretation of this transition as the gravity dual of confinement/deconfinement. We also show that similar results hold for the phenomenologically motivated soft wall model, underlying the potential universality of our analysis. Related Links


10:4011:00  Schvellinger, M (Oxford)  
AdS/QCD and kaon decays  Sem 1  
I will discuss holographic dual models of QCDlike theories at strong coupling. This will include recent developments of gauge theories at finite temperature based on brane thermodynamics. 

11:0011:30  Coffee  
11:3011:50  Hidaka, Y (RBRC)  
Real time effective theory in a hot gauge theory with a Z(N) interface  Sem 1  
We explore real time phenomena such as plasma oscillations and Debye screening in a SU(N) gauge theory with a Z(N) interface at high temperature, where the Z(N) symmetry is spontaneously broken. The Z(N)interface is obtained as a solution between different Z(N) vacua. In the background we show that gluons and quarks have unusual distributions, and gluon mass and Debye screening mass are changed. We construct a realtime effective theory in the background. 

11:5012:10  Nakamura, S (Hanyang)  
A holographic dual of QGP hydrodynamics  Sem 1  
We consider a gravity dual description of time dependent, strongly interacting largeNc N=4 SYM. We regard the gauge theory system as a fluid with shear viscosity. Our fluid is expanding in one direction following the Bjorken's picture that is relevant to RHIC experiments. We obtain the dual geometry at the late time that is consistent with dissipative hydrodynamics. We show that the integration constants that cannot be determined by hydrodynamics are given by looking at the horizon of the dual geometry. 

12:1012:30  Grosse, J (Jagiellonian, Krakow)  
Meson Spectra of an expanding plasma  Sem 1  
We consider an expanding boostinvariant plasma using AdS/CFT. We determine the timedependence of the meson spectrum in the latetime regime and recover the N=4 results asymptotically. 

12:3013:30  Lunch at Wolfson Court  
14:0014:30  Bringoltz, B (Oxford)  
Strings in SU(N) gauge theories: zero and nonzero temperature  Sem 1  
We calculate the energy spectrum of strings in (2+1)dimensional SU(N) gauge theories with N=2,3,4,5,6,8. We first focus on zero temperature nd calculate the tensions of strings in different SU(N) representations. We attempt to control various systematic errors, and for the fundamental representation this allows us to compare with the analytic prediction of Karabali, Kim, and Nair. In this case we find that the prediction deviates from our results by at most 3%, which is statistically significant. We proceed to discuss the temperature dependence of the Polyakov loops' spectrum in the confined phase and compare it to the free bosonic string model. For the ground state we find that this model provides a very good approximation for our results, even relatively close to the deconfinement transition. We discuss how our results evolve with the lattice spacing, the number of colors, and make a connection with our previous calculation for the Hagedorn temperature in 3+1 dimensions. Related Links


14:3015:30  Verbaarschot, J (State University of New York)  
Phases of QCD: perspectives, challenges and opportunities  Sem 1  
We will give a critical discussion of the phase diagram of QCD in the temperature  chemical potential plane. We will explain the mechanism of chiral symmetry breaking at nonzero chemical potential and emphasize the importance of the the phase of the fermion determinant. Among others it is shown that the BanksCasher formula, which relates the chiral condensate and the Dirac spectrum, is not valid for QCD at nonzero chemical potential. Instead, because of the phase of the fermion determinant, intricate cancellations lead to a nonzero chiral condensate. The distribution of this phase is calculated by means of chiral perturbation theory, and a region of the phase diagram where Monte Carlo simulations can be performed is identified. 

15:3016:00  Tea  
16:0017:00  Yaffe, L (Washington)  
Heavy quarks in strongly coupled N=4 plasma  Sem 1  
18:4519:30  Dinner at Wolfson Court (Residents only) 