Minimal spontaneous baryogenesis from flavor

Abstract

In its minimal realization, the Froggatt-Nielsen (FN) mechanism addresses the Standard Model (SM) flavor puzzle via the spontaneous breaking of a horizontal $U(1)_H$ symmetry. If $U(1)_H$ is global and broken before the end of inflation, it gives rise to a pseudo-Nambu-Goldstone boson (axion-like particle) with a homogeneous initial misalignment, whose subsequent coherent evolution sources spontaneous $CPT$ violation in the SM sector. We show that in the presence of $B-L$-violating processes $-$ parametrized here model-independently via the dimension-five Weinberg operator responsible for light neutrino masses $-$ the minimal FN setup can generate the baryon asymmetry of the Universe (BAU), linking the origin of flavor directly to the BAU and neutrino masses. Solving a complete set of evolution equations for SM asymmetries, we demonstrate that this mechanism can readily yield a baryon asymmetry comparable to the observed value, or even exceeding it by several orders of magnitude. Accounting for baryonic isocurvature and entropy dilution from axion decays, we find that the observed BAU is successfully reproduced for axion oscillation temperatures above $10^{11}$ GeV and axion decay constants ranging from $10^{13\cdots 14}$ GeV to above $10^{17}$ GeV. Finally, while we focus on a global $U(1)_H$ symmetry and axion motion from standard misalignment, our framework is readily extendable to other global horizontal symmetries and arbitrary axion motion.