Direct Detection of Electroweak-Interacting Dark Matter

Assuming that the lightest neutral component in an SU(2)L gauge multiplet is the main ingredient of dark matter in the universe, we calculate the elastic scattering cross section of the dark matter with nucleon, which is an important quantity for the direct detection experiments. When the dark matter is a real scalar or a Majorana fermion which has only electroweak gauge interactions, the scattering with quarks and gluon are induced through one- and two-loop quantum processes, respectively, and both of them give rise to comparable contributions to the elastic scattering cross section. We evaluate all of the contributions at the leading order and find that there is an accidental cancellation among them. As a result, the spin-independent cross section is found to be O(10^-(46-48)) cm^2, which is far below the current experimental bounds.Comment: 19 pages, 7 figures, published versio

An N=2 SUSY Gauge Model for Dynamical Breaking of the Grand Unified SU(5) Symmetry

We construct an extension of the recently proposed dynamical model for the breaking of SU(5)$_{\rm GUT}$ gauge symmetry, in which a pair of massless chiral supermultiplets for Higgs doublets are naturally obtained. We point out that a model at a specific point in the parameter space of superpotential is regarded as a low-energy effective theory of an N=2 supersymmetric gauge model for the strongly interacting hypercolor sector.Comment: 7 page

Exact Results for Soft Supersymmetry Breaking Parameters in Supersymmetric Gauge Theories

We obtain exact relations (valid to all orders in the coupling constant) for the running gaugino mass in supersymmetric gauge theories, treating the soft supersymmetry breaking effects in the linear approximation. If a supersymmetry breaking squark (selectron) mass term is introduced, our relation connects the renormalization group equation for this term with that for the gaugino mass. Exact relations for the threshold effects in the gaugino masses are derived. The key ingredients of our analysis is the use of the Wilsonean action and holomorphy of this action with respect to relevant parameters.Comment: One correction, one reference added; the final version to be published in Phys. Rev.

Flavor and CP Violation Induced by Atmospheric Neutrino Mixing

Neutrino oscillation experiments suggest existence of new flavor-violating interactions in high energy scale. It may be possible to probe them by the flavor- and CP-violating processes in leptons and hadrons in the supersymmetric (SUSY) models. In this article the third-generation flavor violation is reviewed in the SUSY seesaw model and SUSY SU(5) GUT with the right-handed neutrinos.Comment: 12 pages. Talk at Fujihara Seminar on Neutrino Mass and Seesaw Mechanism (SEESAW 1979-2004), Tsukuba, Ibaraki, Japan, 23-25 Feb 200

Slepton Oscillation at Large Hadron Collider

Measurement of Lepton-Flavor Violation (LFV) in the minimal SUSY Standard Model (MSSM) at Large Hadron Collider (LHC) is studied based on a realistic simulation. We consider the LFV decay of the second-lightest neutralino, $\tilde{\chi}^0_2 \to \tilde{l} l' \to l l' \tilde{\chi}^0_1$, in the case where the flavor mixing exists in the right-handed sleptons. We scan the parameter space of the minimal supergravity model (MSUGRA) and a more generic model in which we take the Higgsino mass $\mu$ as a free parameter. We find that the possibility of observing LFV at LHC is higher if $\mu$ is smaller than the MSUGRA prediction; the LFV search at LHC can cover the parameter range where the $\mu \to e \gamma$ decay can be suppressed by the cancellation among the diagrams for this case.Comment: 29 pages, 10 figure

Probing physics beyond the standard model from lepton sector

In this review we discuss physics of the lepton sector, the anomalous dipole moment of muon, the charged lepton-flavor violation, and the electric dipole moments of charged leptons, from viewpoints of the minimal supersymmetric standard model and the extensions.Comment: ICRR-Report-487-2002-5, 10 pages;Talk given in The Fifth KEK Topical Conference (KEKTC5), KEK, Tsukuba, Japan, November 200

Neutrino Oscillation and Charged Lepton-Flavor Violation in the Supersymmetric Standard Models

The neutrino experiment results suggest that the neutrinos have finite masses and the lepton-flavor symmetries are violating in nature. In the supersymmetric models, the charged lepton-flavor violating processes, such as mu -> e gamma and tau -> mu gamma, may have the branching ratios accessible to the future experiments, depending on origins of the neutrino masses and the SUSY breaking. In this paper we discuss the branching ratios in the supergravity scenario using the current solar and atmospheric neutrino experimental data.Comment: 12 pages. Talk given at the Workshop on High Intensity Muon Sources (HIMUS99), Tsukuba, Japan, 1-4 Dec 199