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research article

Chiral magnetohydrodynamics with zero total chirality

Brandenburg, Axel
•
Kamada, Kohei
•
Mukaida, Kyohei
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September 28, 2023
Physical Review D

We study the evolution of magnetic fields coupled with chiral fermion asymmetry in the framework of chiral magnetohydrodynamics with zero initial total chirality. The initial magnetic field has a turbulent spectrum peaking at a certain characteristic scale and is fully helical with positive helicity. The initial chiral chemical potential is spatially uniform and negative. We consider two opposite cases where the ratio of the length scale of the chiral plasma instability (CPI) to the characteristic scale of the turbulence is smaller and larger than unity. These initial conditions might be realized in cosmological models, including certain types of axion inflation. The magnetic field and chiral chemical potential evolve with inverse cascading in such a way that the magnetic helicity and chirality cancel each other at all times, provided there is no spin flipping. The CPI timescale is found to determine mainly the time when the magnetic helicity spectrum attains negative values at high wave numbers. The turnover time of the energy-carrying eddies, on the other hand, determines the time when the peak of the spectrum starts to shift to smaller wave numbers via an inverse cascade. The onset of helicity decay is determined by the time when the chiral magnetic effect becomes efficient at the peak of the initial magnetic energy spectrum, provided the CPI does not grow much. When spin flipping is important, the chiral chemical potential vanishes at late times and the magnetic helicity becomes constant, which leads to a faster increase of the correlation length. This is in agreement with what is expected from magnetic helicity conservation and also happens when the initial total chirality is imbalanced. Our findings have important implications for baryogenesis after axion inflation.

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Type
research article
DOI
10.1103/PhysRevD.108.063529
Web of Science ID

WOS:001093991600003

Author(s)
Brandenburg, Axel
Kamada, Kohei
Mukaida, Kyohei
Schmitz, Kai
Schober, Jennifer Waltraud  
Date Issued

2023-09-28

Publisher

American Physical Society

Published in
Physical Review D
Volume

108

Issue

6

Article Number

063529

Subjects

Physical Sciences

•

Primordial Magnetic-Fields

•

Baryon Number

•

Equilibrium

•

Decay

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LASTRO  
FunderGrant Number

Swedish Research Council

2019-04234

NASA ATP

80NSSC22K0825

JSPS KAKENHI

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Available on Infoscience
February 19, 2024
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/204116
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