The Chiral MagnetoHydroDynamics of QCD fluid at RHIC and LHC

TL;DR

This paper reviews recent theoretical and experimental progress on the Chiral Magnetic Effect in QCD fluids produced in heavy ion collisions at RHIC and LHC, highlighting its potential role in observed charge asymmetry fluctuations.

Contribution

It provides a concise summary of recent developments and future tests regarding the Chiral Magnetic Effect in relativistic hydrodynamics of QCD plasma.

Findings

Evidence of charge asymmetry fluctuations at LHC and RHIC.

Disappearance of charge asymmetry fluctuations at low RHIC energies.

Theoretical insights into the role of anomalies in hydrodynamics.

Abstract

The experimental results on heavy ion collisions at RHIC and LHC indicate that QCD plasma behaves as a nearly perfect fluid described by relativistic hydrodynamics. Hydrodynamics is an effective low-energy Theory Of Everything stating that the response of a system to external perturbations is dictated by conservation laws that are a consequence of the symmetries of the underlying theory. In the case of QCD fluid produced in heavy ion collisions, this theory possesses anomalies, so some of the apparent classical symmetries are broken by quantum effects. Even though the anomalies appear as a result of UV regularization and so look like a short distance phenomenon, it has been realized recently that they also affect the large distance, macroscopic behavior in hydrodynamics. One of the manifestations of anomalies in relativistic hydrodynamics is the Chiral Magnetic Effect (CME). At this conference, a number of evidences for CME have been presented, including i) the disappearance of charge asymmetry fluctuations in the low-energy RHIC data where the energy density is thought to be below the critical one for deconfinement; ii) the observation of charge asymmetry fluctuations in Pb-Pb collisions at the LHC. Here I give a three-page summary of some of the recent theoretical and experimental developments and of the future tests that may allow to establish (or to refute) the CME as the origin of the observed charge asymmetry fluctuations.