Generating a seed magnetic field à la the chiral Biermann battery

Cosmological and astrophysical observations indicate the presence of a magnetic field over all scales. In order to explain these magnetic fields, it is assumed that there exists a seed magnetic field which gets amplified by dynamos. These seed fields may have been produced during inflation, at phase transitions, or during some turbulent phase of the early Universe. One well-known mechanism to get the seed field is the Biermann battery, which was originally discussed in the context of generation in an astrophysical object. Requirements for this mechanism to work are (i) a nonzero gradient of the electron number density and pressure, and (ii) they are nonparallel to each other. In the present article we propose a similar mechanism to generate the seed field but in an inhomogeneous chiral plasma. Our mechanism works, in the presence of chiral anomaly, by the virtue of inhomogeneity in the chiral chemical potential and temperature. We discuss various scenarios where inhomogeneities in the chemical potential and temperature can arise. We find that, depending on the epoch of generation, the strength of the seed magnetic fields varies from a few nanogauss (nG) to a few hundred nG.