# Effects of magnetic field on the plasma evolution in relativistic heavy-ion collisions

## TL;DR

This paper uses relativistic magnetohydrodynamics simulations to explore how strong magnetic fields influence plasma evolution, flow fluctuations, and related phenomena in ultrarelativistic heavy-ion collisions, revealing complex effects on elliptic flow and magnetic flux reorganization.

## Contribution

It introduces detailed RMHD simulations to analyze magnetic field effects on plasma dynamics and flow fluctuations in heavy-ion collisions, highlighting novel phenomena like flux reorganization and quadrupolar magnetic fields.

## Key findings

- Magnetic fields enhance elliptic flow at small impact parameters.
- Magnetic flux can temporarily increase due to plasma fluctuations.
- Strong magnetic fields cause even-odd patterns in flow coefficient spectra.

## Abstract

Very strong magnetic fields can arise in non-central heavy-ion collisions at ultrarelativistic energies, which may not decay quickly in a conducting plasma. We carry out relativistic magnetohydrodynamics (RMHD) simulations to study the effects of this magnetic field on the evolution of the plasma and on resulting flow fluctuations in the ideal RMHD limit. Our results show that magnetic field leads to enhancement in elliptic flow for small impact parameters while it suppresses it for large impact parameters (which may provide a signal for initial stage magnetic field). Interestingly, we find that magnetic field in localized regions can temporarily increase in time as evolving plasma energy density fluctuations lead to reorganization of magnetic flux. This can have important effects on chiral magnetic effect. Magnetic field has non-trivial effects on the power spectrum of flow fluctuations. For very strong magnetic field case one sees a pattern of even-odd difference in the power spectrum of flow coefficients arising from reflection symmetry about the magnetic field direction if initial state fluctuations are not dominant. We discuss the situation of nontrivial magnetic field configurations arising from collision of deformed nuclei and show that it can lead to anomalous elliptic flow. Special (crossed body-body) configurations of deformed nuclei collision can lead to presence of quadrupolar magnetic field which can have very important effects on the rapidity dependence of transverse expansion (similar to {\it beam focusing} from quadrupole fields in accelerators).