Fumihiko Toyoda

Phase Transitions in the NMSSM

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.

Multiquark baryons and color screening at finite temperature

We study baryons in SU(N) gauge theories at finite temperature according to the gauge/string correspondence based on IIB string theory. The baryon is constructed out of the D5-brane and N fundamental strings to form a color singlet N-quark bound state. At finite temperature and in the deconfining phase, we could find k(<N)-quark baryons. Thermal properties of such k-quark baryons and also of the N-quark baryon are examined. We study the temperature dependence of color screening distance and the Debye length of the baryon of the k quark and the N quark. We also estimate the melting temperature, where the baryons decay into quarks and gluons completely.

CP Violation in the Higgs Sector and a Phase Transition in the MSSM

We investigate the electroweak phase transition in the presence of a large CP violation in the squark sector of the MSSM. When the CP violation is large, scalar-pseudoscalar mixing of the Higgs bosons occurs, and a large CP violation in the Higgs sector is induced. It, however, weakens the first-order phase transition before the mixing reaches its maximal level. Even when the CP violation in the squark sector is not so large that the phase transition is strongly first order, the phase difference between the broken and symmetric phase regions grows to O(1), which leads to successful baryogenesis when the charged Higgs bosons are light.

Transitional CP Violation in the MSSM and Electroweak Baryogenesis

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

Spontaneous CP violation at finite temperature in the MSSM

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Sphalerons in the NMSSM

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.

CP-Violating Bubble Wall and Electroweak Baryogenesis

By studying the effective potential of the MSSM at finite temperature, we find that CP can be spontaneously broken in the intermediate region between the symmetric and broken phases separated by the bubble wall created at the phase transition. If CP is violated in this manner, there could be a bubble wall connecting CP conserving vacua and violating CP halfway, which would result in sufficient baryon asymmetry of the universe.

CP-Violating Profile of the Electroweak Bubble Wall

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 a wide range of parameter values, in spite of the negative contribution from the cubic term in the Higgs potential.

Numerical approach to CP violating Dirac equation

The electroweak baryogenesis depends on the profile of the CP-violating bubble wall created at the first order phase transition. We attempt to determine it by solving the coupled equations of motion for the moduli and phases of the two Higgs doublets at the transition temperature. A variety of CP-violating bubble walls are classified by boundary conditions. We point out that a sufficiently small explicit CP violation gives nonperturbative effects to yield the baryon asymmetry of the universe.The electroweak baryogenesis depends on the profile of the CP-violating bubble wall created at the first order phase transition. We attempt to determine it by solving the coupled equations of motion for the moduli and phases of the two Higgs doublets at the transition temperature. A variety of CP-violating bubble walls are classified by boundary conditions. We point out that a sufficiently small explicit CP violation gives nonperturbative effects to yield the baryon asymmetry of the universe.

Baryonium in confining gauge theories

In any scenario of the electroweak baryogenesis, the profile of the CP violating bubble wall, created at the first-order phase transition, playc an essential role. We attempt to determine it by solving the equations of motion for the scalars in the two-Riggs-doublet model at the transition temperature. According to the parameters in the potential, we found three solutions. Two of them smoothly connect the CP-violating broken phase and the symmetric phase, while the other connects CP-conserving vacua but violates CP in the intermediate region. We also estimate the chiral charge flux, which will be turned into the baryon density in the symmetric phase by the sphaleron process.In any scenario of the electroweak baryogenesis, the profile of the CP violating bubble wall, created at the first-order phase transition, plays an essential role. We attempt to determine it by solving the equations of motion for the scalars in the two-Higgs-doublet model at the transition temperature. According to the parameters in the potential, we found three solutions. Two of them smoothly connect the CP-violating broken phase and the symmetric phase, while the other connects CP-conserving vacua but violates CP in the intermediate region. We also estimate the chiral charge flux, which will be turned into the baryon density in the symmetric phase by the sphaleron process.