Baryogenesis from scalar dynamics in the primordial Universe

Department of Physics, Indian Institute of Technology Guwahati - Guwahati 781 039, India

Received: 11 July 2025
Accepted: 13 March 2026

Abstract

We investigate a non-supersymmetric mechanism for baryogenesis driven by the nonlinear dynamics of a complex scalar field Φ with a self-interaction term that explicitly breaks the global U(1) symmetry. This self-interaction leads to dynamical generation of asymmetry associated with the U(1) sector in the primordial Universe. The coupled nonlinear dynamical equations governing the real and imaginary components of Φ, evolving in an expanding radiation-dominated background, induce different trajectories for the scalar charge components. Our numerical computation reveals that the resulting Noether charge density decays as at late times. Since the photon density in a radiation-dominated Universe also scales as , the Noether charge-to-photon ratio asymptotically approaches a constant in the long-time limit, . We find that this asymmetry mechanism can operate across different scales, with lower masses requiring weaker interactions and higher masses demanding stronger couplings for the scalar field.