Recent development of hydrodynamic modeling in heavy-ion collisions

Abstract

We present a concise review of the recent development of relativistic hydrodynamics and its applications to heavy-ion collisions. Theoretical progress on the extended formulation of hydrodynamics towards out-ofequilibrium systems is addressed, emphasizing the so-called attractor solution. On the other hand, recent phenomenological improvements in the hydrodynamic modeling of heavy-ion collisions with respect to the ongoing Beam Energy Scan program, the quantitative characterization of transport coefficients in the three-dimensionally expanding quark-gluon plasma, the fluid description of small colliding systems, and some other interdisciplinary connections are discussed.

Convergence of hydrodynamic modes: insights from kinetic theory and holography

“…As originally found in reference [34] for the real k case, ω ⊥ can cross the branch cut joining ω + bp and ω − bp . 2 This crossing does not entail that ω ⊥ ceases to exist [35]; it just means that ω ⊥ migrates to a different sheet of the retarded two-point function defined by analytical continuation. While this branch cut crossing does not pose any obstruction to the convergence of the series expansion of ω ⊥ around k = 0, it has to be taken into account when obtaining ω ⊥ numerically.…”

“…Understanding the foundations of relativistic hydrodynamics as a description of nonequilibrium physics has been an important research theme of the past decade. The experimental motivation behind it comes from the field of ultrarelativistic heavy-ion collisions, where relativistic hydrodynamics is the framework successfully used to connect the early time physics of quantum chromodynamics (QCD) with the properties of the particle spectrum in the detectors [1,2]. On the theoretical side, how the hydrodynamic regime emerges from QCD in particular and quantum field theories in general has turned out to be a subject ripe for discoveries.…”

Transseries for causal diffusive systems

“…Apart from MIS itself, examples of theories featuring a diffusion-to-sound crossover described 3 by the telegrapher's equation include quantum fluctuating superconductors [34], systems breaking spatial translations spontaneously in the presence of phase relaxation [35] and, in the AdS/CFT context, probe branes at finite temperature and large baryon density [36][37][38], models of momentum relaxation [39], higherderivative gravity [40,41], and constructions based on generalized global symmetries that describe dynamical electromagnetism in the boundary QFT [42,43] or viscoelastic media [44]. 4 Furthermore, with a straightforward modification, our methods also apply to the chiral magnetic waves in the presence of axial charge relaxation discussed in [46,47]. These observations suggest that the results we will derive in this work are potentially relevant for a wide range of distinct physical systems.…”

“…Understanding nonequilibrium phenomena with hydrodynamic tails has been a very active research direction of the past two decades. One motivation for this quest has been ultrarelativistic heavy-ion collisions at RHIC and LHC and the success of hydrodynamic modelling there [1][2][3][4]. Another set of motivations came from condensed matter and quantummany body physics [5].…”

“…In the AdS/CFT context, the natural counterpart of this problem would be a shear channel fluctuation in all-order hydrodynamics as discussed in[31,32] 3. It is worth remarking that the telegrapher's equation might only emerge in a suitable parametric limit 4. See also[45] for an embedding of the telegrapher's equation into a field-theoretic context.…”