TY - JOUR

T1 - Efficiency of dynamos from an autonomous generation of chiral asymmetry

AU - Schober, Jennifer

AU - Rogachevskii, Igor

AU - Brandenburg, Axel

N1 - Publisher Copyright:
© 2024 American Physical Society.

PY - 2024/8/15

Y1 - 2024/8/15

N2 - At high energies, the dynamics of a plasma with charged fermions can be described in terms of chiral magnetohydrodynamics. Using direct numerical simulations, we demonstrate that chiral magnetic waves (CMWs) can produce a chiral asymmetry μ5=μL-μR from a spatially fluctuating (inhomogeneous) chemical potential μ=μL+μR, where μL and μR are the chemical potentials of left- and right-handed electrically charged fermions, respectively. If the frequency of the CMW is less than or comparable to the characteristic growth rate of the chiral dynamo instability, the magnetic field can be amplified on small spatial scales. The growth rate of this small-scale chiral dynamo instability is determined by the spatial maximum value of μ5 fluctuations. Therefore, the magnetic field amplification occurs during periods when μ5 reaches temporal maxima during the CMW. If the small-scale chiral dynamo instability leads to a magnetic field strength that exceeds a critical value, which depends on the resistivity and the initial value of μ, magnetically dominated turbulence is produced. Turbulence gives rise to a large-scale dynamo instability, which we find to be caused by the magnetic alpha effect. Our results have consequences for the dynamics of certain high-energy plasmas, such as the early Universe.

AB - At high energies, the dynamics of a plasma with charged fermions can be described in terms of chiral magnetohydrodynamics. Using direct numerical simulations, we demonstrate that chiral magnetic waves (CMWs) can produce a chiral asymmetry μ5=μL-μR from a spatially fluctuating (inhomogeneous) chemical potential μ=μL+μR, where μL and μR are the chemical potentials of left- and right-handed electrically charged fermions, respectively. If the frequency of the CMW is less than or comparable to the characteristic growth rate of the chiral dynamo instability, the magnetic field can be amplified on small spatial scales. The growth rate of this small-scale chiral dynamo instability is determined by the spatial maximum value of μ5 fluctuations. Therefore, the magnetic field amplification occurs during periods when μ5 reaches temporal maxima during the CMW. If the small-scale chiral dynamo instability leads to a magnetic field strength that exceeds a critical value, which depends on the resistivity and the initial value of μ, magnetically dominated turbulence is produced. Turbulence gives rise to a large-scale dynamo instability, which we find to be caused by the magnetic alpha effect. Our results have consequences for the dynamics of certain high-energy plasmas, such as the early Universe.

UR - http://www.scopus.com/inward/record.url?scp=85201215369&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.110.043515

DO - 10.1103/PhysRevD.110.043515

M3 - Article

AN - SCOPUS:85201215369

SN - 2470-0010

VL - 110

JO - Physical Review D

JF - Physical Review D

IS - 4

M1 - 043515

ER -