Gravitational Leptogenesis in the Axion Inflation with an SU(2) gauge field

Understand

We present an intrinsic leptogenesis mechanism in models of axion inflation with a classical SU(2) gauge field.

• The gauge field is coupled to the axion with a Chern-Simons interaction and comprises a tiny fraction of the total energy, $\frac{\rho_{_{\rm YM}}}{\rho_{_{\rm tot}}}\lesssim\epsilon^2$.
• However, it has spin-2 fluctuations which breaks the parity and leads to the generation of chiral gravitational waves during inflation.
• By the gravitational anomaly in SM, it naturally creates a net lepton number density, sufficient to explain the matter asymmetry.