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.

In K. Dusling et al. [arXiv:1705.00745.], an initial-state "parton model" of quarks scattering off a dense nuclear target was shown to qualitatively reproduce the systematics of multiparticle azimuthal anisotropy cumulants measured in proton/deuteron-nucleus (pA) collisions at the Relativistic Heavy Ion Collider and the LHC. The systematics included (i) the behavior of the four-particle cumulant c 2 f4g, which generates a real four-particle second Fourier harmonic v 2 f4g; (ii) the ordering v 2 f2g > v 2 f4g ≈ v 2 f6g ≈ v 2 f8g for two-, four-, six-, and eight-particle Fourier harmonics; and (iii) the behavior of so-called symmetric cumulants SC(2,3) and SC(2,4). These features of azimuthal multiparticle cumulants were previously interpreted as a signature of hydrodynamic flow; our results challenge this interpretation. We expand here upon our previous study and present further details and novel results on the saturation scale and transverse momentum (p ⊥ ) dependence of multiparticle azimuthal correlations. We find that the dependence of v 2 f2g and v 2 f4g on the number of color domains in the target varies with the p ⊥ window explored. We extend our prior discussion of symmetric cumulants and compute as yet unmeasured symmetric cumulants. We investigate the N c dependence of v 2 f2g and v 2 f4g. We contrast our results, which include multiple scatterings of each quark off the target, to the Glasma graph approximation, where each quark suffers at most two-gluon exchanges with the target. We find that coherent multiple scattering is essential to obtain a positive definite v 2 f4g. We provide an algorithm to compute expectation values of arbitrary products of the "dipole" lightlike Wilson line correlators.

Qualitative features of multiparticle correlations in light-heavy ion (p+A) collisions at RHIC and LHC are reproduced in a simple initial state model of partons in the projectile coherently scattering off localized domains of color charge in the heavy nuclear target. These include (i) the ordering of the magnitudes of the azimuthal angle nth Fourier harmonics of two-particle correlations v_{n}{2}, (ii) the energy and transverse momentum dependence of the four-particle Fourier harmonic v_{2}{4}, and (iii) the energy dependence of four-particle symmetric cumulants measuring correlations between different Fourier harmonics. Similar patterns are seen in an Abelian version of the model, where we observe v_{2}{2}>v_{2}{4}≈v_{2}{6}≈v_{2}{8} of two, four, six, and eight particle correlations. While such patterns are often interpreted as signatures of collectivity arising from hydrodynamic flow, our results provide an alternative description of the multiparticle correlations seen in p+A collisions.