Baryogenesis from Domain Walls in the Next-to-Minimal Supersymmetric Standard Model

TL;DR

This work explores baryogenesis from domain-wall collapse in the NMSSM, showing that a net baryon asymmetry can arise even when explicit CP violation is gravitationally suppressed, provided CP is spontaneously broken at the wall formation. The authors couple wall dynamics to a small explicit CP-violating bias that governs the collapse, not the direct generation of baryon number, and they demonstrate this using a $Z_3$-symmetric NMSSM with three CP-related vacua. Through both analytic estimates and 2D simulations of wall networks, they find that a net baryon-to-entropy ratio of order $n_B/s \sim 10^{-8}$ is plausible, with a baryogenesis efficiency $\kappa_{BG}$ around $0.2$ under reasonable conditions and $\Delta(\theta_1+\theta_2)\sim 2\pi/3$. The results suggest gravitationally induced CP violation could drive electroweak-scale baryogenesis in models with spontaneous CP breaking, linking Planck-scale physics to early-universe baryogenesis.

Abstract

We consider the production of baryon number from collapsing domain walls, and in particular examine the magnitude of CP violation which is required in such schemes. Taking the conventional solution to the domain wall problem in the Next-to-Minimal Supersymmetric Standard Model as an example, we show that the observed baryon assymmetry of the universe may have been generated, even if the initial {\em explicit} CP violation in the Lagrangian were so small ({\em i.e.} gravitational) that it could never be experimentally detected. This is possible by having the {\em explicit} CP violation affect the way in which the walls collapse, rather than be responsible for the generation of baryon number directly. Net baryon number is created at the domain walls by the spontaneous breaking of CP.