Phenomenological implications of asymmetric AdS5 shock wave collision studies for heavy ion physics

Abstract

This paper discusses possible phenomenological implications for p+A and A+A collisions of the results of recent numerical AdS/CFT calculations examining asymmetric collisions of planar shocks. In view of the extreme Lorentz contraction, we model highly relativistic heavy ion collisions (HICs) as a superposition of collisions between many near-independent transverse "pixels" with differing incident longitudinal momenta. It was found that also for asymmetric collisions the hydrodynamization time is in good approximation a proper time, just like for symmetric collisions, depending on the geometric mean of the longitudinally integrated energy densities of the incident projectiles. For realistic collisions with fluctuations in the initial energy densities, these results imply a substantial increase in the hydrodynamization time for highly asymmetric pixels. However, even in this case the local hydrodynamization time still is significantly smaller than perturbative results for the thermalization time.

QCD thermalization: Ab initio approaches and interdisciplinary connections

“…30, the "high-γ" regime of thin shocks leads to a rich set of transient physics before hydrodynamics becomes applicable. Another important phenomenon, discussed in [535,549,550], is the notion of longitudinal coherence. This notion applies to the "centre-of-mass" frame of high energy collisions and states that the longitudinal structure of projectiles does not leave an imprint on the transient form of the energy-momentum tensor in the postcollision region provided that it is sufficiently localized.…”

Entropy production far from equilibrium in a chiral charged plasma in the presence of external electromagnetic fields

“…Displayed in the figure is a fit to this linear growth with a growth rate of ds/dt = 1.85245. The linear growth of the thermal entropy in the evolution of SYM plasma is not a new phenomenon it was recently seen and discussed in the context of phenomenological insights gained from holographic heavy ion collisions [42] (see their work for more information). It should be noted that the linear growth of the entropy as displayed in [42] occurs before thermalization and without sourcing.…”

“…The linear growth of the thermal entropy in the evolution of SYM plasma is not a new phenomenon it was recently seen and discussed in the context of phenomenological insights gained from holographic heavy ion collisions [42] (see their work for more information). It should be noted that the linear growth of the entropy as displayed in [42] occurs before thermalization and without sourcing. 12 Hence the behavior we observe is by definition of different origin as will be discussed further in this section.…”

“…A powerful method for obtaining information about strongly coupled systems is via holography. There is a vast amount of literature 3 dedicated to thermalization [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], often utilizing Vaidya spacetime, and to the study of dynamical holographic systems as analogues for heavy ion collisions [33][34][35][36][37][38][39][40][41][42]. These studies simulate the evolution of SYM plasmas via numerical evolution of bulk Einstein equations and are meant to mimic the conditions of heavy ion collisions.…”

Holographic Kolmogorov-Sinai entropy and the quantum Lyapunov spectrum

“…16 One interesting statement derived from AdS/CFT is that the quark gluon plasma, produced during heavy ion collisions, thermalizes very quickly [29] on time scales that are just a fraction of 1 fm/c. Even when finite 't Hooft coupling corrections are taken into account [36,37] or non-trivial transverse fluctuations of the energy density are considered [38,39], both of which roughly doubling the thermalization time, one still ends up with a result below 1 fm/c, which does not contradict experimental observations, but rather estimates from weakly coupled, N = 3 YM-calculations [20]. Granted that QCD at high temperatures strongly resembles large N , N = 4 SYM, which according to (6.1) is likely to actually saturate the possible upper bound on the (ensemble averaged) entropy production rate, this mismatch between weak coupling results on the one side and phenomenology and holography on the other side is not surprising.…”