Speaker
Description
Hydrodynamics is an effective theory for the description of long-wavelength phenomena of fluids, that can be expressed as a small gradient expansion of fluid velocities relative to a thermal background. Thus, hydrodynamics is expected to fail for systems which are far-from-equilibrium. The medium produced in pp collisions at LHC and RHIC energies is an example of such a system. However, recent experimental results of high energy pp collision have shown evidence of collectivity similar to those observed in heavy-ion collisions. The unprecedented success of hydrodynamics to describe collectivity in heavy-ion collisions, as well as small systems, can be attributed to the fact that there exists a stable universal attractor which makes the dynamical equations to quickly converge and enter a hydrodynamic regime, at a time scale much smaller than the typical isotropization time scales. In the present work, we go beyond the previous
works which considered 1+1d longitudinal boost invariant systems, by considering a system undergoing Gubser flow which has a simultaneous transverse and longitudinal expansion.
To investigate the dynamics of such a system, the Boltzmann equation is solved in the relaxation time approximation using a hierarchy of angular moments of the distribution function. The dynamics of transition is described by the presence of fixed points which describes the evolution of the system in various stages. We found that unlike 1+1d Bjorken flow which has late-time thermalization (hydrodynamization), Gubser flow is intrinsically a 3+1d expanding system with dynamics such that the system goes from early time free-streaming regime to intermediate thermalization (hydrodynamization) and back to free-streaming in the late time regime. The attractor solution is found for various orders of moments as an interpolation between these fixed points.
