Dynamical Baryogenesis in Rainbow Cosmology

Abstract

We investigate baryogenesis in the framework of rainbow cosmology employing a complex scalar field with a softly broken global $U(1)$-symmetry. The modified dispersion relation of rainbow cosmology leads to energy-dependent modification to the FLRW metric components, that modifies the Friedmann equation and the scalar field dynamics. We thereby obtain analytical solutions for the scalar field evolution in the radiation-dominated epoch, and show that baryon asymmetry is generated dynamically even from an initially baryon-symmetric state. We find that the baryon-to-photon ratio asymptotically approaches a constant value in the long-time limit, which is proportional to the symmetry-breaking coupling strength $λ$, and scales with the scalar field mass as $M^{-5/2}$. Our results demonstrate that requiring consistency with the observed baryon asymmetry constrains the $λ$ and $M$ values within reasonable ranges, thus providing a viable dynamical mechanism for baryogenesis during the radiation-dominated era without invoking supersymmetry.