Wednesday 20 September 2017
to 15:00 at
Igor Rogachevskii (Ben-Gurion University and Nordita)
The magnetohydrodynamic (MHD) description of plasmas with relativistic
particles necessarily includes an additional new field, the chiral
chemical potential associated with the axial charge (i.e., the
number difference between right- and left-handed relativistic fermions).
This chiral chemical potential gives rise to a contribution to the electric
current density of the plasma (chiral magnetic effect).
We present a self-consistent treatment of the chiral
MHD equations, which include the back-reaction of the magnetic
field on a chiral chemical potential and its interaction
with the plasma velocity field.
A number of novel phenomena are exhibited.
We show that the chiral magnetic effect decreases
the frequency of the Alfven wave for incompressible
flows, increases the frequencies of the Alfven wave
and of the fast magnetosonic wave for compressible flows,
and decreases the frequency of the slow magnetosonic wave.
In the presence of turbulence with vanishing mean kinetic helicity,
the derived mean-field chiral MHD equations
describe turbulent large-scale dynamos caused by the chiral alpha effect,
which is not related to kinetic helicity and
is dominant for large fluid and magnetic Reynolds numbers.
Using numerical simulations, we show that in chiral MHD, magnetic field
evolution proceeds in distinct stages:
(i) small-scale chiral dynamo instability;
(ii) first nonlinear stage when the Lorentz force drives
(iii) development of inverse energy transfer
with a k^-2 magnetic energy spectrum;
(iv) generation of large-scale magnetic field
by chiral magnetically driven turbulence,
decrease of the chiral chemical potential, saturation,
and eventual decay.
These dynamo effects may have interesting consequences
in the dynamics of the early universe, neutron stars,
and the quark--gluon plasma.