Michael Strickland

Dissipative Dynamics of Highly Anisotropic Systems

In this paper we present a method to improve the description of 0+1 dimensional boost invariant dissipative dynamics in the presence of large momentum-space anisotropies. We do this by reorganizing the canonical hydrodynamic expansion of the distribution function around a momentum-space anisotropic ansatz rather than an isotropic equilibrium one. At leading order the result obtained is two coupled ordinary differential equations for the momentum-space anisotropy and typical momentum of the degrees of freedom. We show that this framework can reproduce both the ideal hydrodynamic and free streaming limits. Additionally, we demonstrate that when linearized the differential equations reduce to 2nd order Israel-Stewart viscous hydrodynamics. Finally, we make quantitative comparisons of the evolution of the pressure anisotropy within our approach and 2nd order viscous hydrodynamics in both the strong and weak coupling limits.

Hard-loop dynamics of non-abelian plasma instabilities

I discuss recent advances in the understanding of non-equilibrium gauge field dynamics in plasmas which have particle distributions which are locally anisotropic in momentum space. In contrast to locally isotropic plasmas such anisotropic plasmas have a spectrum of soft unstable modes which are characterized by exponential growth of transverse (chromo)-magnetic fields at short times. The long-time behavior of such instabilities depends on whether or not the gauge group is abelian or non-abelian. Here I will report on recent numerical simulations which attempt to determine the long-time behavior of an anisotropic non-abelian plasma within hard-loop effective theory.

Thermal Bottomonium Suppression at RHIC and LHC

Abstract In this paper we consider the suppression of bottomonium states in ultrarelativistic heavy ion collisions. We compute the suppression as a function of centrality, rapidity, and transverse momentum for the states ϒ ( 1 s ) , ϒ ( 2 s ) , ϒ ( 3 s ) , χ b 1 , and χ b 2 . Using this information, we then compute the inclusive ϒ ( 1 s ) suppression as a function of centrality, rapidity, and transverse momentum including feed down effects. Calculations are performed for both RHIC s NN = 200 GeV Au–Au collisions and LHC s NN = 2.76 TeV Pb–Pb collisions. From the comparison of our theoretical results with data available from the STAR and CMS Collaborations we are able to constrain the shear viscosity to entropy ratio to be in the range 0.08 η / S 0.24 . Our results are consistent with the creation of a high temperature quark–gluon plasma at both RHIC and LHC collision energies.

Hard-Thermal-Loop Resummation of the Free Energy of a Hot Gluon Plasma

We calculate the free energy of a hot gluon plasma to leading order in hard-thermal-loop perturbation theory. Effects associated with screening, gluon quasiparticles, and Landau damping are resummed to all orders. The ultraviolet divergences generated by the hard-thermal-loop propagator corrections can be canceled by a counterterm which depends on the thermal gluon mass. The deviation of the hard-thermal-loop free energy from lattice QCD results for T{gt}2T{sub c} has the correct sign and roughly the correct magnitude to be accounted for by next-to-leading order corrections. {copyright} {ital 1999} {ital The American Physical Society}

Dynamics of Quark-Gluon-Plasma Instabilities in Discretized Hard-Loop Approximation

Non-abelian plasma instabilities have been proposed as a possible explanation for fast isotropization of the quark-gluon plasma produced in relativistic heavy-ion colli- sions. We study the real-time evolution of these instabilities in non-abelian plasmas with a momentum-space anisotropy using a hard-loop effective theory that is discretized in the velocities of hard particles. We extend our previous results on the evolution of the most un- stable modes, which are constant in directions transverse to the direction of anisotropy, from gauge group SU(2) to SU(3). We also present first full 3+1-dimensional simulation results based on velocity-discretized hard loops. In contrast to the effectively 1+1-dimensional transversely constant modes we find subexponential behavior at late times.

Three-loop HTLpt thermodynamics at finite temperature and chemical potential

A bstractWe calculate the three-loop thermodynamic potential of QCD at finite temperature and chemical potential(s) using the hard-thermal-loop perturbation theory (HTLpt) reorganization of finite temperature and density QCD. The resulting analytic thermodynamic potential allows us to compute the pressure, energy density, and entropy density of the quark-gluon plasma. Using these we calculate the trace anomaly, speed of sound, and second-, fourth-, and sixth-order quark number susceptibilities. For all observables considered we find good agreement between our three-loop HTLpt calculations and available lattice data for temperatures above approximately 300 MeV.

Instabilities of an anisotropically expanding non-Abelian plasma: 1D+3V discretized hard-loop simulations

We study the (3+1)-dimensional evolution of non-Abelian plasma instabilities in the presence of a longitudinally expanding background of hard particles using the discretized hard loop framework. The free streaming background dynamically generates a momentum-space anisotropic distribution which is unstable to the rapid growth of chromomagnetic and chromoelectric fields. These fields produce longitudinal pressure that works to isotropize the system. Extrapolating our results to energies probed in ultrarelativistic heavy-ion collisions we find, however, that a pressure anisotropy persists for a few fm/c. In addition, on time scales relevant to heavy-ion collisions we observe continued growth of plasma instabilities in the strongly non-Abelian regime. Finally, we find that the longitudinal energy spectrum is well-described by a Boltzmann distribution with increasing temperature at intermediate time scales.

HTL Perturbation Theory to Two Loops

We calculate the pressure for pure-glue QCD at high temperature to two-loop order using hard-thermal-loop (HTL) perturbation theory. At this order, all the ultraviolet divergences can be absorbed into renormalizations of the vacuum energy density and the HTL mass parameter. We determine the HTL mass parameter by a variational prescription. The resulting predictions for the pressure fail to agree with results from lattice gauge theory at temperatures for which they are available.

Resummation in hot field theories

Abstract There has been significant progress in our understanding of finite-temperature field theory over the past decade. In this paper, we review the progress in perturbative thermal field theory focusing on thermodynamic quantities. We first discuss the breakdown of naive perturbation theory at finite temperature and the need for an effective expansion that resums an infinite class of diagrams in the perturbative expansion. This effective expansion which is due to Braaten and Pisarski, can be used to systematically calculate various static and dynamical quantities as a weak-coupling expansion in powers of g. However, it turns out that the weak-coupling expansion for thermodynamic quantities are useless unless the coupling constant is very small. We critically discuss various ways of reorganizing the perturbative series for thermal field theories in order to improve its convergence. These include screened perturbation theory (SPT), hard-thermal-loop perturbation theory, the Φ-derivable approach, dimensionally reduced (DR) SPT, and the DR Φ-derivable approach.

QUARKONIA IN THE QUARK GLUON PLASMA

In this paper, we review recent progress toward understanding the nature of quarkonia in the quark gluon plasma. We review the theory necessary to understand the melting of bound states due to color-screening, including lattice results for the heavy quark poten- tial, lattice results on the correlation functions related to the relevant spectral functions, and the emergence of a complex-valued potential in high-temperature quantum chromo- dynamics. We close with a brief survey of phenomenological models of quarkonium sup- pression in relativistic heavy ion collisions.