Nordita Astrophysics Seminars

Decay law of helical magnetic turbulence with chiral fermions

by Axel Brandenburg (Nordita, Stockholm)

Albano 3:6228 - Mega (22 seats) (Albano Building 3)

Albano 3:6228 - Mega (22 seats)

Albano Building 3



In relativistic plasmas of sufficiently high temperature, fermion chirality can be interchanged with magnetic helicity while preserving the total chirality through the quantum chiral anomaly. Here we show, using a high resolution numerical simulation, that in the case of zero total chirality, where the magnetic helicity density balances with the appropriately scaled chiral chemical potential to zero, the magnetic energy density decays and the correlation length increases with time just like in nonhelical turbulence with vanishing chiral chemical potential. But here, the magnetic helicity density is nearly maximum and shows a novel scaling with time $t$ proportional to $t^{-2/3}$. This is unrelated to the $t^{-2/3}$ decay of magnetic {\it energy} in fully helical magnetic turbulence. The modulus of the chiral chemical potential decays in the same fashion. These decay laws can be determined from the conservation of what is known as the Hosking integral, adapted here to include the effect of the chiral chemical potential. We compute the adapted Hosking integral and confirm that it is indeed approximately conserved.