Small Quarkonium states in an anisotropic QCD plasma

We determine the hard-loop resummed propagator in an anisotropic QCD plasma in general covariant gauges and define a potential between heavy quarks from the Fourier transform of its static limit. We find that the potential exhibits angular dependence and that binding of very small quarkonium states is stronger than in an isotropic plasma.Comment: 4 pages, Contribution to Quark Matter 2008 (Jaipur, India

HEAVY QUARKONIA ABOVE DECONFINEMENT.

In this talk I summarize our current understanding of quarkonium states above deconfinement based on phenomenological and lattice QCD studies

Melting Sequence of Quarkonia

In this talk I discuss what we can learn about quarkonium dissociation from lattice-potential based models, and summarize the current understanding of lattice data on quarkonium

Quarkonium above deconfinement as an open quantum system

Quarkonium at temperatures above deconfinement is modeled as an open quantum system, whose dynamics is determined not just by a potential energy and mass, but also by a drag coefficient which characterizes its interaction with the medium. The reduced density matrix for a heavy particle experiencing dissipative forces is expressed as an integral over paths in imaginary time and evaluated numerically. We demonstrate that dissipation could affect the Euclidean heavy-heavy correlators calculated in lattice simulations at temperatures just above deconfinement.Comment: 13 pages, 1 figur

Confinement and Chiral Symmetry

We illustrate why color deconfines when chiral symmetry is restored in gauge theories with quarks in the fundamental representation, and while these transitions do not need to coincide when quarks are in the adjoint representation, entanglement between them is still present.Comment: 4 pages, 1 figure, proceedings of Quark Matter 200

A path integral for heavy-quarks in a hot plasma

We propose a model for the propagation of a heavy-quark in a hot plasma, to be viewed as a first step towards a full description of the dynamics of heavy quark systems in a quark-gluon plasma, including bound state formation. The heavy quark is treated as a non relativistic particle interacting with a fluctuating field, whose correlator is determined by a hard thermal loop approximation. This approximation, which concerns only the medium in which the heavy quark propagates, is the only one that is made, and it can be improved. The dynamics of the heavy quark is given exactly by a quantum mechanical path integral that is calculated in this paper in the Euclidean space-time using numerical Monte Carlo techniques. The spectral function of the heavy quark in the medium is then reconstructed using a Maximum Entropy Method. The path integral is also evaluated exactly in the case where the mass of the heavy quark is infinite; one then recovers known results concerning the complex optical potential that controls the long time behavior of the heavy quark. The heavy quark correlator and its spectral function is also calculated semi-analytically at the one-loop order, which allows for a detailed description of the coupling between the heavy quark and the plasma collective modes

The Quark-Mass Dependence of T_C in QCD: Working up from m=0 or down from m=infinity ?

We analyze the dependence of the QCD transition temperature on the quark (or pion) mass. We find that a linear sigma model, which links the transition to chiral symmetry restoration, predicts a much stronger dependence of T_c on m_pi than seen in present lattice data for m_pi >~ 0.4 GeV. On the other hand, working down from m_pi=infinity, an effective Lagrangian for the Polyakov loop requires only small explicit symmetry breaking, b_1 ~ exp(-m_pi), to describe T_c(m_pi) in the above mass range. Physically, this is a consequence of the flat potential (large correlation length) for the Polyakov loop in the three-color pure gauge theory at T_c. We quantitatively estimate the end point of the line of first order deconfining phase transitions: m_pi = 1.8 GeV and Tc = 240 MeV for three flavors and three colors.Comment: 9 pages, 3 figures; v2: renormalization of vacuum fluctuations in the linear sigma model and some references added; final version to appear in PR

Real and imaginary-time QQˉQ\bar{Q} correlators in a thermal medium

We investigate the behavior of a pair of heavy fermions, denoted by $Q$ and $\bar{Q}$, in a hot/dense medium. Although we have in mind the situation where $Q$ and $\bar{Q}$ denote heavy quarks, our treatment will be limited to simplified models, which bear only some general similarities with QCD. We study in particular the limiting case where the mass of the heavy fermions is infinite. Then a number of results can be derived exactly: a Schr\"odinger equation can be established for the correlator of the heavy quarks; the interaction effects exponentiate, leading to a simple instantaneous effective potential for this Schr\"odinger equation. We consider simple models for the medium in which the $Q\bar Q$ pair propagates. In the case where the medium is a plasma of photons and light charged fermions, an imaginary part develops in this effective potential. We discuss the physical interpretation of this imaginary part in terms of the collisions between the heavy particles and the light fermions of the medium; the same collisions also determine the damping rate of the heavy fermions. Finally we study the connection between the real-time propagator of the heavy fermion pair and its Euclidean counterpart, and show that the real part of the potential entering the Schr\"odinger equation for the real-time propagator is the free energy calculated in the imaginary-time formalism.Comment: 32 pages, 8 figure