Gauss-Bonnet Chern-Simons gravitational wave leptogenesis

Understand

The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly.

• We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term.
• We find that the lepton production can be exponentially enhanced.
• The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales.