Gravitational leptogenesis in axion inflation with SU(2) gauge field

Abstract

We present an intrinsic leptogenesis mechanism in models of axion inflation\nwith a classical SU(2) gauge field. The gauge field is coupled to the axion\nwith a Chern-Simons interaction and comprises a tiny fraction of the total\nenergy, $\\frac{\\rho_{_{\\rm YM}}}{\\rho_{_{\\rm tot}}}\\lesssim\\epsilon^2$.\nHowever, it has spin-2 fluctuations which breaks the parity and leads to the\ngeneration of chiral gravitational waves during inflation. By the gravitational\nanomaly in SM, it naturally creates a net lepton number density, sufficient to\nexplain the matter asymmetry. We show that this mechanism can generate the\nobserved value of baryon to photon number density in a natural range of\nparameters and yet has a small chiral tensor power spectrum on large scales.\n