Decay Rate Asymmetry of Top Squark

We discuss a decay rate asymmetry of the top squark, which is induced by a new source of CP violation intrinsic in the supersymmetric standard model. Although new sources of CP violation in this model are severely constrained from the electric dipole moment of the neutron, an unsuppressed CP-violating phase can still coexist with a top squark whose mass is accessible by near-future colliders. Then the dominant decay mode of the top squark has a width different from its CP conjugate process. The magnitude of this $CP$ asymmetry becomes of order $10^{-3}$.Comment: 11 pages, 1 figur

CPCP violation in minimal supersymmetric standard model

$CP$ violating phenomena predicted by the minimal supersymmetric standard model are discussed in a case where the $CP$ violating phases in SUSY sector are not suppressed. The electric dipole moments of the neutron and the electron are large, but can be smaller than their experimental upper bounds if the scalar quarks and leptons are heavier than a few TeV. $T$ violating asymmetries in the production processes of the different neutralino pair and the different chargino pair emerge at the tree level. They could be as large as of order $10^{-2}$ in unpolarized electron beam experiments and $10^{-1}$ in polarized electron beam experiments. In a pair production of the charginos of the same mass, the asymmetry emerges through the electric and the weak "electric" dipole moments of the charginos at the loop level, but its magnitude is at most of order $10^{-4}$.Comment: 7 pages with 7 figures, TKU-HEP 94/02; IFM 2/94, LaTeX with Elsevir Science Publisher's style file, espcrc2.sty. (To appear in the proceedings of the Third KEK Topical Conference on CP Violation, November 1993) Figures are not included. The complete PostScript file can be obtained by anonymous ftp from ape.sp.u-tokai.ac.jp in the directr

Constraints on Light Top Squark from B0B^0-Bˉ0\bar{B}^0 mixing

We discuss the constraints on the mass of the lighter top squark from \bbbar\ mixing in the minimal supersymmetric standard model. A light top squark whose mass is less than half of the $Z^0$-boson mass has not yet been excluded from direct search experiments at LEP. However, the existence of the light top squark may exceedingly enhance \bbbar\ mixing, owing to the box diagrams exchanging the charginos and the up-type squarks. We show that for a sizable region of parameter space the light top squark contribution to \bbbar\ mixing becomes the same order of magnitude as the standard $W$-boson contribution. Taking into account the experimental results for \bbbar\ and \kkbar\ mixings, the existence of the light top squark is excluded in an appreciable region of the parameter space which LEP experiments have not ruled out.Comment: 8 pages latex file, 2 figure

Supersymmetric Extension of the Standard Model with Naturally Stable Proton

A new supersymmetric standard model based on N=1 supergravity is constructed, aiming at natural explanation for the proton stability without invoking an ad hoc discrete symmetry through R parity. The proton is protected from decay by an extra U(1) gauge symmetry. Particle contents are necessarily increased to be free from anomalies, making it possible to incorporate the superfields for right-handed neutrinos and an SU(2)-singlet Higgs boson. The vacuum expectation value of this Higgs boson, which induces spontaneous breakdown of the U(1) symmetry, yields large Majorana masses for the right-handed neutrinos, leading to small masses for the ordinary neutrinos. The linear coupling of SU(2)-doublet Higgs superfields, which is indispensable to the superpotential of the minimal supersymmetric standard model, is replaced by a trilinear coupling of the Higgs superfields, so that there is no mass parameter in the superpotential. The energy dependencies of the model parameters are studied, showing that gauge symmetry breaking is induced by radiative corrections. Certain ranges of the parameter values compatible with phenomena at the electroweak energy scale can be derived from universal values of masses-squared and trilinear coupling constants for scalar fields at a very high energy scale.Comment: 32 pages, Revtex, 7 figure

A Supersymmetric Model with an Extra U(1) Gauge Symmetry

In the standard model the proton is protected from decay naturally by gauge symmetries, whereas in the ordinary minimal supersymmetric standard model an ad hoc discrete symmetry is imposed for the proton stability. We present a new supersymmetric model in which the proton decay is forbidden by an extra U(1) gauge symmetry. Particle contents are necessarily increased to be free from anomalies, incorporating right-handed neutrinos. Both Dirac and Majorana masses are generated for neutrinos, yielding non-vanishing but small masses. The superpotential consists only of trilinear couplings and the mass parameter $\mu$ of the minimal model is induced by spontaneous breaking of the U(1) symmetry.Comment: 10 pages, Revte

Large effects on \BsBs mixing by vector-like quarks

We calculate the contributions of the vector-like quark model to \BsBs mixing, taking into account the constraints from the decay $B\to X_s\gamma$. In this model the neutral bosons mediate flavor-changing interactions at the tree level. However, \BsBs mixing is dominated by contributions from the box diagrams with the top quark and the extra up-type quark. In sizable ranges of the model parameters, the mixing parameter $x_s$ is much different from the standard model prediction.Comment: 11 pages, 4 figures, To be published in Phys. Rev.

Supersymmetric predictions for the inclusive b→sγb\to s\gamma decay

We study the penguin induced transition $b\to s\ \gamma$ in the minimal N=1 supersymmetric extension of the Standard Model with radiative breaking of the electroweak group. We include the effects of one-loop corrections to the Higgs potential and scalar masses. We show that the present upper and lower experimental limits on the inclusive decay sharply constrain the parameter space of the model in a wide range of $\tan\beta$ values. The implications of the recently advocated relation $|B|\ge 2$ for the bilinear SUSY soft breaking parameter in grand unified theories are also analyzed.Comment: 23 pages + 12 figures (hardcopies available on request), LATEX, SISSA 40/94/E

T-Violation in K+→μ+νγK^+ \to \mu^+ \nu \gamma Decay And Supersymmetry

Measurement of the transverse muon polarization $P^{\bot}_{\mu}$ in the $K^+ \rightarrow \mu^+\nu\gamma$ decay will be attempted for the first time at the ongoing KEK E246 experiment and also at a proposed BNL experiment. We provide a general analysis of how $P^{\bot}_{\mu}$ is sensitive to the physical $CP$-violating phases in new physics induced four-Fermi interactions, and then we calculate the dominant contributions to $P^{\bot}_{\mu}$ from squark family mixings in generic supersymmetric models. Estimates of the upper bounds on $P^{\bot}_{\mu}$ are also given. It is found that a supersymmetry-induced right-handed quark current from $W$ boson exchange gives an upper limit on $P^{\bot}_{\mu}$ as large as a few per cent, whereas with charged-Higgs-exchange induced pseudoscalar interaction, $P^{\bot}_{\mu}$ is no larger than a few tenths of a per cent. Possible correlations between the muon polarization measurements in $K^+ \rightarrow \mu^+\nu\gamma$ and $K^+ \rightarrow \pi^0\mu^+\nu$ decays are discussed, and distinctive patterns of this correlation from squark family-mixings and from the three-Higgs-doublet model are noted.Comment: Revtex, 29 pages including 4 epsf figure

Antisymmetric Higgs representation in SO(10) for neutrinos

A Model based on SO(10) grand unified theory (GUT) and supersymmetry is presented to describe observed phenomena for neutrinos. The large mixing angles among different generations, together with the small masses, are attributed to the Higgs boson structure at the GUT energy scale. Quantitative discussions for these observables are given, taking into account their energy evolution.Comment: 10 page

Analysis of CP Violation in Neutralino Decays to Tau Sleptons

In the minimal supersymmetric standard model, tau sleptons $\tilde \tau_{1,2}$ and neutralinos $\tilde \chi^0_{1,2}$ are expected to be among the lightest supersymmetric particles that can be produced copiously at future $e^+e^-$ linear colliders. We analyze $\tilde \tau$ pair and $\tilde \chi_1^0 \tilde \chi_2^0$ production under the assumption $m_{\tilde \chi_1^0} < m_{\tilde \tau_1} < m_{\tilde \chi_2^0}$, allowing the relevant parameters of the SUSY Lagrangian to have complex phases. We show that the transverse and normal components of the polarization vector of the $\tau$ lepton produced in $\tilde \chi_2^0$ decays offer sensitive probes of these phases.Comment: LaTeX, 30 pages with 10 .eps figure