Akira Kakuto

Aspects of Grand Unified Models with Softly Broken Supersymmetry

The minimal S U(3)× S U(2)× U(1) gauge model with softly broken supersymmetry is studied in the framework of the standard grand unification. It is assumed that the supersymmetry is left intact at an energy scale μ≃ M_X, the grand unification mass scale, except for Majorana masses of gauge fermions. The other soft breaking parameters at low energies are shown to be generated by renormalization effects. The gauge symmetry breaking S U(2)× U(1)→ U(1)em is also caused through radiative corrections. The super-GIM mechanism apparently works well to suppress flavor changing neutral interactions. The mass of the top quark is remarkably found to be constrained as 60 GeV ≾ mt ≾ 180 GeV. Futhermore various mass relations for unconventional particles are obtained as well as crude estimates for numerical masses of them. It is found that there is a plethola of new particles in a mass range from a few tens of GeV to a few hundred GeV.

Renormalization of Supersymmetry Breaking Parameters Revisited

On considere les equations du groupe de renormalisation dans le modele de jauge minimal SU(3)×SU(2)×U(1) a supersymetrie brisee doucement

The Effective Potential of Electroweak Theory with Two Massless Higgs Doublets at Finite Temperature

The effective potential of electroweak theory with two massless Higgs doublets at finite temperature is studied. We investigate phase structure and critical temperature in this model by numerical analysis without high-temperature expansion. The phase transition is found to be of first order. The critical temperature is shown to be relatively low for typical scalar masses. The free energy of the critical bubble is calculated with some approximations and we find that the bubble nucleation can occur at a temperature a little below the critical temperature. We also discuss the possibility of the electroweak baryogenesis

Spontaneous CP violation at finite temperature in the MSSM

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.

Weak-Symmetry Breaking in Locally Supersymmetric Grand Unified Theories

A possibility of the radiative breaking of the weak gauge symmetry is studied in the framework of grand unified theories coupled to the N = 1 supergravity. Some supersymmetry breaking mass parameters in the effective low energy theory, which do not emerge at the tree level from the spontaneous breakdown of the N = 1 supergravity, are found to become sizable when the loop effect of heavy particles is taken into account at the grand unification mass scale. These mass parameters, as well as those produced at the tree level, are considered as boundary values at the unification mass scale for the renormalization group equations. It is remarkably found that there isa possibility that the top quark can be as light as the present experimental lower bound in order for the radiative weak symmetry breaking to occur. It is further shown that gluinos acquire phenomenologically allowable masses even if the canonical kinetic term is assumed for the Yang-Mills supergravity coupling. Wiggsinos (i.e., mixed states of gauge and Higgs fermions) also obtain sizable masses.

Fermion scattering off a CP-violating electroweak bubble wall.

A general prescription to solve the Dirac equation in the presence of CP-violating electroweak bubble wall is presented. The profile of the bubble wall is not specified except that the wall height is

Sphalerons in the NMSSM

m_0

CP-Violating Bubble Wall and Electroweak Baryogenesis

and zero deep in the broken- and the symmetric-phase regions, respectively, where

CP-Violating Profile of the Electroweak Bubble Wall

m_0

Numerical approach to CP violating Dirac equation

is a fermion mass given by the Higgs-vacuum-expectation value and the Yukawa coupling. The CP-violating effects are evaluated by regarding CP-violating part of the bubble wall as a perturbation to CP-conserving solutions. The basic quantity,