Nordita Astrophysics seminars

Chiral Magnetic Effect

by Prof. Igor Rogachevskii (Ben-Gurion University of the Negev)

11:028 ()


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 small-scale turbulence; (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.