Dynamical magnetic fields in heavy-ion collisions

TL;DR

This paper investigates how the evolution of magnetic fields in heavy-ion collisions is affected by the medium's electrical conductivity, using numerical solutions of Maxwell's equations coupled with hydrodynamics.

Contribution

It provides a detailed numerical analysis of the medium's effect on magnetic field evolution, highlighting the importance of conductivity and expansion dynamics.

Findings

Magnetic fields are significantly enhanced at late times due to medium effects.

The magnitude of magnetic fields depends on the medium's electric conductivity.

The expansion of the fireball influences the magnetic field evolution.

Abstract

The magnetic fields in heavy-ion collisions are important ingredients for many interesting phenomena, such as the Chiral Magnetic Effect, Chiral Magnetic Wave, the directed flow $v_1$ of $D^0$ mesons and the splitting of the spin polarization of the $\Lambda$/$\bar{\Lambda}$. Quantitative studies of these phenomena however suffer from limited understanding on the dynamical evolution of these fields in the medium created by the collisions, which remains a critical and challenging problem. The initial magnetic fields from the colliding nuclei decay very fast in the vacuum but their lifetime could be extended through medium response due to electrically conducting quarks and antiquarks. Here we perform a detailed analysis of such medium effect on the dynamical magnetic fields by numerically solving the Maxwell's equations concurrently with the expanding medium described by viscous hydrodynamics, under the assumption of negligible back reaction of the fields on the fluid evolution. Our results suggest a considerable enhancement of late time magnetic fields, the magnitude of which depends sensitively on the fireball expansion as well as the medium electric conductivity both before and during hydrodynamic stage.