Off-equilibrium sphaleron transitions in the glasma

Abstract

We perform first classical-statistical real time lattice simulations of topological transitions in the non-equilibrium Glasma of weakly coupled but highly occupied gauge fields created immediately after the collision of ultra-relativistic nuclei. Simplifying our description by employing SU(2) gauge fields, and neglecting their longitudinal expansion, we find that the rate of topological transitions is initially strongly enhanced relative to the thermal sphaleron transition rate and decays with time during the thermalization process. Qualitative features of the time dependence of this nonequilibrium transition rate can be understood when expressed in terms of the magnetic screening length, which we also extract non-perturbatively. A detailed investigation of auto-correlation functions of the Chern-Simons number (N CS ) reveals non-Markovian features of the evolution distinct from previous simulations of non-Abelian plasmas in thermal equilibrium.

Effective kinetic description of the expanding overoccupied glasma

“…It is challenging to perform controlled computations of infrared dynamics in a gauge theory as have been performed for a scalar theory, or even interpret this IR dynamics definitively as a BEC. However, as we noted previously, recent computations of the spatial string tension in the Glasma [24,25] provide an essential guidepost for future studies.…”

“…It has been observed that the spatial string tension sets the scale for off-equilibrium sphaleron transitions [24]; this latter quantity is essential for dynamical simulations [26,27] of the Chiral Magnetic effect.…”

“…Our results therefore argue for a deeper understanding and characterization of the IR dynamics in the Glasma. Key features of this dynamics are captured by the spatial string tension, which has a characteristic time dependence [24] that is universal [25].…”

Non-Abelian chiral instabilities at high temperature on the lattice

“…On the one hand state-of-the-art simulations (see, e.g., refs. [81,82]) now incorporate by default the expanding geometry of the heavy-ion collision region and make close contact with the saturation picture for the incident nuclei. The fact that the gauge field modes do not fill up the spectrum up to the cutoff in these simulations contrary to the thermal case, makes them systematically better controlled.…”

World-line approach to chiral kinetic theory in topological background gauge fields

“…The matter at these early times is a strongly correlated "Glasma"-state [16,17,18] formed from the decay of highy occupied Color Glass Condensates [19,20,21] and its dynamics is captured by ab initio classical-statistical real time lattice simulations [22,23,24]. These methods can be extended to compute off-equilibrium sphaleron rates in the Glasma [25], which are seen to be significantly larger than the rate of sphaleron transitions in the thermalized Quark-Gluon Plasma [26].…”