arXiv subjects

Ken-ichi Okumura

Publications and source records attributed to Ken-ichi Okumura.

31 records · Page 2Linked to original sources

arXiv2004

Flavor Structure of Scherk-Schwarz Supersymmetry Breaking and Constraints from Low Energy Processes

5D orbifold has two attractive features: quasi-localized matter fields can naturally reproduce hierarchical Yukawa coupling, while supersymmetry breaking is inherently built in by the Scherk-Schwarz mechanism. We examine the consequence of this quasi-localization and the Scherk-Schwarz supersymmetry breaking in low energy flavor violating processes, under the assumption that physics below the compactification scale is described by the minimal supersymmetric standard model (MSSM) and find $BR(μ\to e,γ)$ and $ε_K$ impose stringent constraint on flavor structure of the Scherk-Schwarz supersymmetry breaking. Chirality measurement in lepton flavor violating processes is crucial to deduce the surviving flavor structure.

hep-ph↗

arXiv2004

Scherk-Schwarz Supersymmetry Breaking for Quasi-localized Matter Fields and Supersymmetry Flavor Violation

We examine the soft supersymmetry breaking parameters induced by the Scherk-Schwarz (SS) boundary condition in 5-dimensional orbifold field theory in which the quark and lepton zero modes are quasi-localized at the orbifold fixed points to generate the hierarchical Yukawa couplings. In such theories, the radion corresponds to a flavon to generate the flavor hierarchy and at the same time plays the role of the messenger of supersymmetry breaking. As a consequence, the resulting soft scalar masses and trilinear $A$-parameters of matter zero modes at the compactification scale are highly flavor-dependent, thereby can lead to dangerous flavor violations at low energy scales. We analyze in detail the low energy flavor violations in SS-dominated supersymmetry breaking scenario under the assumption that the compactification scale is close to the grand unification scale and the 4-dimensional effective theory below the compactification scale is given by the minimal supersymmetric standard model. Our analysis can be applied to any supersymmetry breaking mechanism giving a sizable $F$-component of the radion superfield, e.g. the hidden gaugino condensation model.

hep-ph↗

arXiv2004

Weakened Constraints from $b \to s γ$ on Supersymmetry Flavor Mixing Due to Next-To-Leading-Order Corrections

We examine the process $B \to X_s γ$ in minimal supersymmetry (SUSY) with general squark flavor mixings. We include all relevant next--to--leading order (NLO) QCD corrections and dominant NLO SUSY effects from the gluino. We find that gluino--squark corrections to down--type quark masses induce large NLO corrections to the dominant Wilson coefficients whose size is often similar to those at LO, especially at large $\tanβ$. For $μ>0$, destructive interference, and suppression by the renormalization group running lead to a ``focusing effect'' of reducing the size of gluino corrections to the branching ratio, and also of reducing the LO sensitivity to flavor mixings among squarks. Constraints from $B(B \to X_s γ)$ on the SUSY--breaking scale can become significantly weakened relative to the minimal flavor violation case, even, at large $\tanβ$, for small flavor mixings. The case of $μ<0$ can also becomes allowed.

hep-ph↗

arXiv2003

Electroweak Symmetry Breaking in Supersymmetric Gauge-Higgs Unification Models

We examine the Higgs mass parameters and electroweak symmetry breaking in supersymmetric orbifold field theories in which the 4-dimensional Higgs fields originate from higher-dimensional gauge supermultiplets. It is noted that such gauge-Higgs unification leads to a specific boundary condition on the Higgs mass parameters at the compactification scale, which is independent of the details of supersymmetry breaking mechanism. With this boundary condition, phenomenologically viable parameter space of the model is severely constrained by the condition of electroweak symmetry breaking for supersymmetry breaking scenarios which can be realized naturally in orbifold field theories. For instance, if it is assumed that the 4-dimensional effective theory is the minimal supersymmetric standard model with supersymmetry breaking parameters induced mainly by the Scherk-Schwarz mechanism, a correct electroweak symmetry breaking can not be achieved for reasonable range of parameters of the model, even when one includes additional contributions to the Higgs mass parameters from the auxiliary component of 4-dimensional conformal compensator. However if there exists a supersymmetry breaking mediated by brane superfield, sizable portion of the parameter space can give a correct electroweak symmetry breaking.

hep-ph↗

arXiv2003

Large Beyond-Leading-Order Effects in b -> s gamma in Supersymmetry with General Flavor Mixing

We examine squark--gluino loop effects on the process $b \to s γ$ in minimal supersymmetry with general flavor mixing in the squark sector. In the regime of heavy squarks and gluino, we derive analytic expressions for the beyond--LO corrections to the Wilson coefficients and find them to be often large, especially at large $\tanβ$ and $μ>0$. The ensuing ranges of values of the Wilson coefficients are typically smaller than in the LO approximation, and sometimes even change sign. This has the effect of often reducing, relative to the LO, the magnitude of supersymmetric contributions to $BR(B \to X_s γ)$. This ``focusing effect'' is caused by contributions from: (i) an RG evolution of the Wilson coefficients; (ii) a correction to the LO chargino contribution to the Wilson coefficients, which can considerably reduce the LO gluino contribution. This partial cancellation of the two contributions takes place only in the case of general flavor mixing. As a result, stringent lower bounds on the mass scale of superpartners, which apply in the case of minimal flavor violation, can be substantially reduced for even small departures from the scenario. The often disfavored case of $μ<0$ can also become allowed for $M_{SUSY}$ as small as $\sim$ 200 GeV, compared to > $\sim$ 500 GeV at LO and over 2 TeV in the case of minimal flavor violation. Limits on the allowed amount of flavor mixing among the 2nd and 3rd generation down--type squarks are also typically considerably weakened. The input CKM matrix element $K^{(0)}_{cb}$ can be larger than the experimental value by a factor of ten, or can be as small as zero.

hep-ph↗

arXiv2002

$B \to X_s γ$ in minimal supersymmetric standard model with general flavor mixing

We present the results of our analysis on $b \to s γ$ in the minimal supersymmetric standard model with a general flavor mixing in the squark sector. We identify the next--to--leading order focusing effect, which considerably reduces the gluino contribution to $b \to s γ$ relative to the leading order calculation. We illustrate that $BR(B \to X_s γ)$ is still very sensitive to the flavor mixing parameters, $δ^d_{ll}$ and $δ^d_{lr}$ so that the lower bound for $m_{1/2}$ obtained in the minimal flavor violation can be easily removed even at $μ<0$, while it is rather stable against $δ^d_{rr}$ and $δ^d_{rl}$.

hep-ph↗

arXiv2001

Lepton flavor violating process in a supersymmetric grand unified theory with right-handed neutrino

Motivated from the recent results of neutrino oscillation experiment, we investigated lepton flavor violating (LFV) processes in a SU(5) supersymmetric grand unified theory with right-handed neutrino. The current experimental upper bound for $μ\to eγ$ process gives already some constraint on the model. Correlation between $μ\to e γ$ and the SUSY contribution to the muon anomalous magnetic moment is also discussed. Future LFV experiments will give considerable impacts on this type of SUSY GUT models equipped with seesaw neutrino mass generation.

hep-ph↗

arXiv2001

Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino

Motivated by the large mixing angle solutions for the atmospheric and solar neutrino anomalies, flavor changing neutral current processes and lepton flavor violating processes as well as the muon anomalous magnetic moment are analyzed in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to explain realistic mass relations for quarks and leptons, we take into account effects of higher dimensional operators above the GUT scale. It is shown that the supersymmetric (SUSY) contributions to the CP violation parameter in $K^0-\bar{K}^0$ mixing, $ε_K$, the $μ\to e γ$ branching ratio, and the muon anomalous magnetic moment become large in a wide range of parameter space. We also investigate correlations among these quantities. Within the current experimental bound of $\text{B}(μ\to e γ)$, large SUSY contributions are possible either in the muon anomalous magnetic moment or in $ε_K$. In the former case, the favorable value of the recent muon anomalous magnetic moment measurement at the BNL E821 experiment can be accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa phase can be different from the prediction within the Standard Model (SM) and therefore the measurements of the CP asymmetry of $B\to J/ψK_S$ mode and $Δm_{B_s}$ could discriminate this case from the SM. We also show that the $τ\to μγ$ branching ratio can be close to the current experimental upperbound and the mixing induced CP asymmetry of the radiative B decay can be enhanced in the case where the neutrino parameters correspond to the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.

hep-ph↗

arXiv2000

Neutrino Yukawa couplings and FCNC processes in B decays in SUSY-GUT

Flavor changing neutral current and lepton flavor violating processes are studied in the SU(5) SUSY-GUT with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of $b \to s γ$ can be as large as 20%. We also show that the $B_s$-$\bar{B}_s$ mixing can be significantly different from the standard model prediction.

hep-ph↗

arXiv2000

$μ\to e γ$ and $μ\to 3e$ Processes with Polarized Muon and Supersymmetric Grand Unified Theories

Lepton flavor violating processes $μ\to e γ$ and $μ\to 3e$ with polarized muons are studied in the supersymmetric grand unified theory (SUSY GUT). As a result of a detailed numerical calculation, it is shown that the P- and T-odd asymmetries defined with the help of the muon polarization and the ratio of two branching fractions make a good contrast between the SU(5) and SO(10) SUSY GUT. These observables are useful to extract differences of the two theories. In particular, the P-odd asymmetry of $μ\to e γ$ varies 100%--100% in SO(10) whereas it is 100% in SU(5) and the T-odd asymmetry of $μ\to 3e$ can reach 15% in SU(5) within the EDM constraints whereas it is small in SO(10).

hep-ph↗

arXiv2000

Neutrino oscillation, SUSY GUT and B decay

Effects of supersymmetric particles on flavor changing neutral current and lepton flavor violating processes are studied in the supersymmetric SU(5) grand unified theory with right-handed neutrino supermultiplets. Using input parameters motivated by neutrino oscillation, it is shown that the time-dependent CP asymmetry of radiative B decay can be as large as 30% when the $τ\to μγ$ branching ratio becomes close to the present experimental upper bound. We also show that the $B_s$--$\bar{B}_s$ mixing can be significantly different from the presently allowed range in the standard model.

hep-ph↗

arXiv1999

$μ\to e γ$ and $μ\to 3e$ processes with polarized muons and supersymmetric grand unified theories

$μ^{+} \to e^{+} γ$ and $μ^{+} \to e^{+}e^{+}e^{-}$ processes are analyzed in detail with polarized muons in supersymmetric grand unified theories. We first present Dalitz plot distribution for $μ^{+} \to e^{+}e^{+}e^{-}$ decay based on effective Lagrangian with general lepton-flavor-violating couplings and define various P- and T-odd asymmetries. We calculate branching ratios and asymmetries in supersymmetric SU(5) and SO(10) models taking into account complex soft supersymmetry breaking terms. Imposing constraints from experimental bounds on the electron, neutron and atomic electric dipole moments, we find that the T-odd asymmetry for $μ^{+} \to e^{+}e^{+}e^{-}$ can be 15% in the SU(5) case. P-odd asymmetry with respect to muon polarization for $μ^{+} \to e^{+} γ$ varies from -20% to -100% for the SO(10) model while it is $+100%$ in the SU(5) case. We also show that the P-odd asymmetries in $μ^{+} \to e^{+}e^{+}e^{-}$ and the ratio of $μ^{+} \to e^{+}e^{+}e^{-}$ and $μ^{+} \to e^{+} γ$ branching fractions are useful to distinguish different models.

hep-ph↗

arXiv1998

CP violation in the $μ\to 3e$ process and supersymmetric grand unified theory

A triple vector correlation in the $μ^{+} \to e^{+} e^{+} e^{-}$ decay with polarized muons is investigated as a probe to CP violating coupling constants in supersymmetric models. A sizable triple correlation can be induced due to a complex phase in the supersymmetric soft-breaking terms in the SU(5) grand unified theory. Correlation with the electric dipole moments of electron and neutron are investigated and it is shown that these quantities give independent information on possible CP violating sources.

hep-ph↗