Sterile Neutrinos in a Grand Unified Model

The recent experimental results indicating the neutrino oscillations may strongly suggest that at least one more light neutrino species is required in order to reconcile the existing data. In the simple GUT frameworks, this fact seems difficult to preserve the parallelism between quarks and leptons. In this letter, we investigate an SO(10) grand unified model with a pair of extra generations in addition to the known three ones. Using the GUT relations, the obtained neutrino mass matrix naturally indicates that one of the SU(2) singlet (sterile) neutrino is very light and has large mixing with muon neutrino, which can explain the atmospheric neutrino anomaly, and the hot dark matter neutrino is also provided. The solar neutrino problem can be solved by the mixing with muon neutrino consistently with quark mixing, namely, the Cabibbo angle.Comment: 15 pages, 5 eps figure

Kaluza-Klein Mediated Supersymmetry Breaking

We discuss a framework for communicating supersymmetry breaking to the visible sector where the radius modulus, which determines the size of extra dimensions, has an auxiliary vacuum expectation value. The modulus couplings generate mass splitting in Kaluza-Klein supermultiplets and they act as messengers of supersymmetry breaking. The soft masses are expressed in terms of renormalization-group functions and the sparticle spectrum is determined by what kind of field propagates in the bulk. This framework also provides new possibilities for solving the supersymmetric flavor problem.Comment: 10 page

Soft Supersymmetry Breaking at Heavy Chiral Threshold

We discuss the structure of threshold corrections to soft supersymmetry-breaking parameters at the mass threshold of heavy chiral superfields. Nontrivial dependence on soft parameters of heavy matter fields originates from the `physical' definition of the threshold scale, at which the general form of soft supersymmetry breaking is derived in the superfield coupling formalism.Comment: 7 pages, no figur

Radiative CP Phases in Supergravity Theories

In this letter, we point out that possible sources of CP violation originate from radiative corrections to soft terms which are ubiquitous in supergravity theories and also in other high-energy frameworks of supersymmetry breaking. With these radiative phases of gaugino masses and scalar couplings, a complex phase of Higgs holomorphic mass parameter is generated via renormalization-group running down to low energy. It is found that its phase value is mainly controlled by wino as well as gluino, which generally receive different radiative corrections to their complex phases, even if the leading part of mass parameters follow from the universality hypothesis. The radiatively generated phases are constrained by the existing experimental bounds on electric dipole moments, and may be detectable in future measurements. They are also found to be available for the cancellation mechanism to be worked.Comment: 14 pages, 5 figures, references adde