Abstract

We show that spontaneous baryogenesis occurs automatically in relaxation models if the reheating temperature is larger than the weak scale, provided the Standard Model fields are charged under the U(1) of which the relaxion is a pseudo-Nambu-Goldstone boson. During the slow roll, the relaxion breaks CPT, biasing the thermal equilibrium in favor of baryons, with sphalerons providing the necessary baryon number violation. We calculate the resulting baryon asymmetry, explore the possible constraints on this scheme and show that there is a swath of parameter space in which the current observations are matched. Successful baryogenesis can be achieved for a range of relaxion masses between 10^-10 and 10^-5 eV. The mechanism operates precisely in the region of parameter space where recent work has shown the relaxion oscillation to be a dark matter candidate.