Chiral plasma instability and primordial Gravitational wave
  It is known that cosmic magnetic field, if present, can generate anisotropic
stress in the plasma and hence, can act as a source of gravitational waves.
These cosmic magnetic fields can be generated at very high temperature, much
above electroweak scale, due to the gravitational anomaly in presence of the
chiral asymmetry. The chiral asymmetry leads to instability in the plasma which
ultimately leads to the generation of magnetic fields. In this article, we
discuss the generation of gravitational waves, during the period of
instability, in the chiral plasma sourced by the magnetic field created due to
the gravitational anomaly. We have shown that such gravitational wave will have
a unique spectrum. Moreover, depending on the temperature of the universe at
the time of its generation, such gravitational waves can have a wide range of
frequencies. We also estimate the amplitude and frequency of the gravitational
waves and delineate the possibility of its detection by future experiments like
eLISA.
