Baryogenesis from cosmological CP breaking

We show that baryogenesis can arise from the cosmological evolution of a scalar field that governs CP-violating parameters, such as the Yukawa couplings and the theta terms of the Standard Model. During the big bang, this scalar may reach a CP-violating minimum, where its mass can be comparable to the inflationary Hubble scale. Such dynamics can emerge in theories featuring either a spontaneously broken local U(1) symmetry or modular invariance. The latter arises naturally as the effective field theory capturing the geometric origin of CP violation in toroidal string compactifications. Modular baryogenesis is compatible with the modular approach to resolving the strong CP problem.