Dr. Michael Strickland receives DOE grant for theoretical study of the quark-gluon plasma
Relativistic heavy ion collision experiments at Brookhaven National Laboratory (BNL) and the European Organization for Nuclear Research (CERN) have made it possible to turn back the clock to approximately one-millionth of a second after the big bang; a time when matter, as we know it, did not exist. At these times the temperature of the universe was approximately 10^12 Kelvin and the protons and neutrons, which constitute the nuclei of atoms, had not yet been formed. Instead, the universe was a super hot quark-gluon plasma. We can now recreate such conditions in the lab and do so over a million times a second. This allows us to study how a super hot QGP cools down under conditions that are very similar to those that existed in the early universe. The large amount of experimental data generated has resulted in extremely high precision measurements concerning the nature of the QGP phase transition. However, in order to model the matter created in these experiments, advanced numerical simulations are required. When making comparisons of theoretical predictions for particle production, collective motion, etc. with data in relativistic nuclear collisions, it is necessary to have a reliable model for the space-time evolution of the temperature, flow velocities, and momentum-space anisotropy of the quark-gluon plasma (QGP) generated in such collisions. As a result, such dynamical models are critically important to all areas of QGP phenomenology. In Spring 2015 Dr. Michael Strickland, Kent State University, Department of Physics, received a two-year grant of $307,000 from the US Department of Energy to support the development of a novel approach to non-equilibrium dynamics in the QGP.
A serious complication for modeling of the QGP is the fact that the matter created in the wake of a heavy ion collision is initially expanding along the beam line direction at nearly the speed of light, without any appreciable transverse expansion. Such an anisotropic expansion causes the momentum-space distribution of the particles which comprise the plasma to also be anisotropic, with the result being that at early times in the QGP local rest frame the particles have a typical longitudinal momentum which is much less than the typical transverse momentum. Due to this, the quark gluon plasma can have a large pressure anisotropy, with the pressure transverse to the beam line far exceeding that along the beam line. The resulting pressure anisotropies cause problems for traditional approaches to dynamical modeling of the quark gluon plasma which rely on the application of linearized relativistic viscous hydrodynamical models. Such models implicitly assume that the system is approximately isotropic in momentum space, with the transverse and longitudinal pressures being approximately equal. Large deviations from isotropy require one to either incorporate higher order terms in the relativistic viscous hydrodynamical equations or to consider revisiting the starting assumptions used in deriving the dynamical equations. Following the latter approach Dr. Strickland has made key advances towards describing such inherently anisotropic plasmas. The resulting dynamical framework has been dubbed anisotropic hydrodynamics (aHydro), and has a wide-ranging applicability in the theoretical study of the quark gluon plasma. Dr. Strickland will continue the development of anisotropic hydrodynamics and use it to make theoretical predictions for a host of observables measured in collider experiments. The project will include development of a public (3+1)d anisotropic hydrodynamics code including a realistic equation of state and anisotropic freeze out. Dr. Strickland will also continue his investigations into the role of non-Abelian plasma instabilities in the thermalization and isotropization of the QGP.