arXiv subjects
Publications and source records attributed to Fumihiko Toyoda.
We study sphaleron solutions in the next-to-minimal supersymmetric standard model. We find that the boundary condition on the singlet field at the origin of the radial coordinate is of Neumann type, while the other boundary conditions are of Dirichlet type. The sphaleron energy takes almost the same value as in the MSSM for wide range of parameters, in spite of the negative contribution from the cubic term in the Higgs potential.
We study phase transitions in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with the weak scale vacuum expectation values of the singlet scalar, constrained by Higgs spectrum and vacuum stability. We find four different types of phase transitions, three of which have two-stage nature. In particular, one of the two-stage transitions admits strongly first order electroweak phase transition, even with heavy squarks. We introduce a tree-level explicit CP violation in the Higgs sector, which does not affect the neutron electric dipole moment. In contrast to the MSSM with the CP violation in the squark sector, a strongly first order phase transition is not so weakened by this CP violation.
Electroweak baryogenesis depends on the profile of the bubble wall created in the first-order phase transition. It is pointed out that CP violation in the Higgs sector of the MSSM could become large enough to explain the baryon asymmetry. We confirm this by solving the equations of motion for the Higgs fields with the effective potential at the transition temperature. That is, we present an example such that the transitional CP violation is realized and show the possibility that the baryon asymmetry of the universe may be produced, if marginally, by the $τ$ lepton interacting with the wall, when an explicit CP breaking in the Higgs sector, which is consistent with experimental bounds, is induced at the phase transition.
We investigate spatial behaviors of the CP-violating angle $θ$ by solving the equation of motion of the two-Higgs-doublet model in the presence of a small explicit CP breaking $δ$. The moduli of the two Higgs scalars are fixed to be the kink shape with a common width. In addition to solutions $θ\sim O(δ)$ in all the region, we find several sets of two solutions of opposite signs, whose magnitudes become as large as $O(1)$ around the surface of the bubble wall while the CP violation in the broken phase limit is of $O(δ)$. Such set of solutions not only yield sufficient amount of the chiral charge flux, but also avoid the cancellation in the net baryon number because of a large discrepancy in their energy densities driven nonperturbatively by the small $δ$.