arXiv subjects

Minoru Tanaka

Publications and source records attributed to Minoru Tanaka.

At least 55 records · Page 3Linked to original sources

arXiv2011

Total curvatures of model surfaces control topology of complete open manifolds with radial curvature bounded below. III

Dedicated to Professor K. Shiohama on the occasion of his seventieth birthday: This article is the third in a series of our investigation on a complete non-compact connected Riemannian manifold $M$. In the first series [arXiv:0901.4010], we showed that all Busemann functions on an $M$ which is not less curved than a von Mangoldt surface of revolution are exhaustions, if the total curvature of the surface is greater than $π$. A von Mangoldt surface of revolution is, by definition, a complete surface of revolution homeomorphic to Euclidean plane whose Gaussian curvature is non-increasing along each meridian. Our purpose of this series is to generalize the main theorem in [arXiv:0901.4010] to an $M$ which is not less curved than a more general surface of revolution.

math.DG↗

arXiv2011

Applications of Toponogov's comparison theorems for open triangles

Recently we generalized Toponogov's comparison theorem to a complete Riemannian manifold with smooth convex boundary, where a geodesic triangle was replaced by an open (geodesic) triangle standing on the boundary of the manifold, and a model surface was replaced by the universal covering surface of a cylinder of revolution with totally geodesic boundary. The aim of this article is to prove splitting theorems of two types as an application. Moreover, we establish a weaker version of our Toponogov comparison theorem for open triangles, because the weaker version is quite enough to prove one of the splitting theorems.

math.DG↗

arXiv2010

H parity and the stable Higgs boson in the SO(5) x U(1) gauge-Higgs unification

In the SO(5) x U(1) gauge-Higgs unification model in the Randall-Sundrum warped space there results the conservation of the H parity. The H parity is assigned to all 4D fields including excited modes in Kaluza-Klein towers. The neutral Higgs boson is the lightest particle of odd H parity, consequently becoming absolutely stable. Its mass is found to be 70 \sim 135 GeV for the warp factor z_L = 10^5 \sim 10^{15}.

hep-ph↗

arXiv2010

Tau longitudinal polarization in B -> D tau nu and its role in the search for charged Higgs boson

We study the longitudinal polarization of the tau lepton in B -> D tau nu decay. After discussing possible sensitivities of tau decay modes to the tau polarization, we examine the effect of charged Higgs boson on the tau polarization in B -> D tau nu. We find a relation between the decay rate and the tau polarization, and clarify the role of the tau polarization measurement in the search for the charged Higgs boson.

hep-ph↗

arXiv2009

Stable Higgs Bosons as Cold Dark Matter

In a class of the gauge-Higgs unification models the 4D neutral Higgs boson, which is a part of the extra-dimensional component of the gauge fields, becomes absolutely stable as a consequence of the gauge invariance and dynamically generated new parity, serving as a promising candidate for cold dark matter (CDM). We show that the observed relic abundance of cold dark matter is obtained in the SO(5) x U(1) model in the warped space with the Higgs mass around 70 GeV. The Higgs-nucleon scattering cross section is found to be close to the current CDMS II and XENON10 bounds in the direct detection of dark matter.

hep-ph↗

arXiv2009

Total curvatures of model surfaces control topology of complete open manifolds with radial curvature bounded below. II

We prove, as our main theorem, the finiteness of topological type of a complete open Riemannian manifold $M$ with a base point $p \in M$ whose radial curvature at $p$ is bounded from below by that of a non-compact model surface of revolution $\tilde{M}$ which admits a finite total curvature and has no pair of cut points in a sector. Here a sector is, by definition, a domain cut off by two meridians emanating from the base point $\tilde{p} \in \tilde{M}$. Notice that our model $\tilde{M}$ does not always satisfy the diameter growth condition introduced by Abresch and Gromoll. In order to prove the main theorem, we need a new type of the Toponogov comparison theorem. As an application of the main theorem, we present a partial answer to Milnor's open conjecture on the fundamental group of complete open manifolds.

math.DG↗

arXiv2008

Patterns of flavor signals in supersymmetric models

Quark and lepton flavor signals are studied in four supersymmetric models, namely the minimal supergravity model, the minimal supersymmetric standard model with right-handed neutrinos, SU(5) supersymmetric grand unified theory with right-handed neutrinos and the minimal supersymmetric standard model with U(2) flavor symmetry. We calculate b --> s(d) transition observables in B_d and B_s decays, taking the constraint from the B_s--B_s-bar mixing recently observed at Tevatron into account. We also calculate lepton flavor violating processes mu --> e gamma, tau --> mu gamma and tau --> e gamma for the models with right-handed neutrinos. We investigate possibilities to distinguish the flavor structure of the supersymmetry breaking sector with use of patterns of various flavor signals which are expected to be measured in experiments such as MEG, LHCb and a future Super B Factory.

hep-ph↗

arXiv2003

Exploring flavor structure of supersymmetry breaking from rare B decays and unitarity triangle

We study effects of supersymmetric particles in various rare B decay processes as well as in the unitarity triangle analysis. We consider three different supersymmetric models, the minimal supergravity, SU(5) SUSY GUT with right-handed neutrinos, and the minimal supersymmetric standard model with U(2) flavor symmetry. In the SU(5) SUSY GUT with right-handed neutrinos, we consider two cases of the mass matrix of the right-handed neutrinos. We calculate direct and mixing-induced CP asymmetries in the b to s gamma decay and CP asymmetry in B_d to phi K_S as well as the B_s--anti-B_s mixing amplitude for the unitarity triangle analysis in these models. We show that large deviations are possible for the SU(5) SUSY GUT and the U(2) model. The pattern and correlations of deviations from the standard model will be useful to discriminate the different SUSY models in future B experiments.

hep-ph↗

arXiv2002

Exploring Flavor Structure of Supersymmetry Breaking at B factories

We investigate flavor physics at present and future B factories in order to distinguish supersymmetric models. We evaluate CP asymmetries in various B decay modes, Delta M(Bd), Delta M(Bs), and epsilon_K in three supersymmetric models, i.e. the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and a supersymmetric model with U(2) flavor symmetry. The allowed regions of Delta M(Bs)/Delta M(Bd) and CP asymmetries in B to J/psi K_S and b to s gamma are different for the three models so that it is possible to distinguish the three models by precise determinations of these observables in near future experiments.

hep-ph↗

arXiv2002

Effects of charged Higgs boson and QCD corrections in $\bar B \to D τ\barν_τ$

We study effects of charged Higgs boson exchange in $\bar B \to D τ\barν_τ$. The Yukawa couplings of Model II of two-Higgs-doublet model, which has the same Yukawa couplings as MSSM, is considered. We evaluate the decay rate including next-to-leading QCD corrections and estimate uncertainties in the theoretical calculation. Our analysis will contribute to probe an extended Higgs sector at B factory experiments.

hep-ph↗

arXiv2002

Exploring Flavor Structure of Supersymmetry Breaking at B factories

We investigate quark flavor signals in three different supersymmetric models, the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and the minimal supersymmetric standard model with U(2) flavor symmetry, in order to study physics potential of the present and future $B$ factories. We evaluate CP asymmetries in various B decay modes, $Δm_{B_s}$, $Δm_{B_d}$, and $ε_K$. The allowed regions of the CP asymmetry in $B\to J/ψK_S$ and $Δm_{B_s}/Δm_{B_d}$ are different for the three models so that precise determinations of these observables in near future experiments are useful to distinguish the three models. We also investigate possible deviations from the standard model predictions of CP asymmetries in other B decay modes. In particular, a large deviation is possible for the U(2) model. The consistency check of the unitarity triangle including $B\to ππ,ρπ,D^{(*)}K^{(*)},D^{(*)}π,D^{*}ρ$, and so on, at future high luminosity $e^+e^-$ $B$ factories and hadronic $B$ experiments is therefore important to distinguish flavor structures of different supersymmetric models.

hep-ph↗

arXiv1998

Lepton-Flavor Violation in the Left-handed Slepton Production at Future Lepton Colliders

The Super-Kamiokande atmospheric neutrino data suggest existence of the large lepton-flavor violating (LFV) interaction in the higher energy scale. If the minimal supersymmetric standard model is extended to have right-handed neutrinos, the left-handed sleptons in the second and third generations are expected to have the LFV masses in the minimal supergravity scenario. In this article we study the LFV signals in the left-handed slepton production at $μ^+μ^-$ colliders and $\e^+\e^-$ linear colliders (LC's), $μ^+μ^-(\e^+\e^-)\toτμ+4jets + \E$ and $μ^+μ^-(\e^+\e^-)\toτμl+ 2jets+ \E$. The main background comes from decay of a tau lepton into a muon in the lepton-flavor conserving slepton pair production. They are significantly reduced by the energy and the impact parameter cuts for the muon. At $μ^+μ^-$ colliders (LC's) it may be possible to reach the mixing angle $\sin 2θ_{\tildeν} \gsim 0.1(0.5)$ and the mass difference $Δm_{\tildeν}\gsim 0.1(0.4)$ GeV for the sneutrinos in the second and third generations at the statistical significance of $3σ$. Such small mass difference and a mixing angle may be induced radiatively even if the Yukawa coupling constant for the tau neutrino is of the order of 0.1.

hep-ph↗

arXiv1998

Unified Explanation of Quark and Lepton Masses and Mixings in the Supersymmetric SO(10) Model

We discussed neutrino masses and mixings in SUSY SO(10) model where quarks and leptons have Yukawa couplings to at least two 10 and one $\bar{126}$ Higgs scalars. In this model, the Dirac and the right-handed Majorana mass terms are expressed by linear combinations of quark and charged lepton mass matrices, which then determine the neutrino mass matrix by the see-saw mechanism. We show that there are various solutions to reproduce a large mixing angle for $ν_μ-ν_τ$ and a small mixing angle for $ν_e-ν_μ$, as well as the hierarchical mass spectrum of neutrinos.

hep-ph↗

arXiv1998

Enhancement of μ\to e γin the supersymmetric SU(5) GUT at large \tanβ

Branching ratio of $μ\to \e γ$ is evaluated in the supersymmetric SU(5) grand unified theory taking account of higher dimensional operators, which reproduce the realistic quark and lepton masses and the mixing parameters. It is shown by numerical calculation that at large $\tanβ$ the branching ratio is enhanced by a few orders of magnitude since the flavor mixings for both the left- and the right-handed sleptons are induced by the effect of the higher dimensional operators.

hep-ph↗

arXiv1997

Lepton flavor violation at linear collider experiments in supersymmetric grand unified theories

Lepton flavor violation at linear collider experiments is discussed. We show that detectable lepton flavor violation could occur through scalar lepton pair production and decay in the supersymmetric SU(5) grand unified theory in spite of the stringent present experimental constraints by rare process searches. Possible cross sections about 40fb for an e+e- collider and 280fb for an e-e- collider are illustrated.

hep-ph↗

arXiv1997

$b \to s \ell\overline{\ell}$ process and multi-Higgs doublet model

Rare $b$ decay processes are analyzed in the multi-Higgs doublet model. Taking account of the constraint from the $b\to s γ$ process, the branching ratio and the forward-backward asymmetry of the final leptons for the $b\to s \ell^+ \ell^-$ process are calculated. It is shown that the branching ratio can be a few times larger than the standard model prediction and the asymmetry can be significantly different from that in the standard model. Combining these observable quantities it is possible to determine complex coupling constants associated with the charged Higgs mixing matrix. The CP violating charge asymmetry in the $b\to s \ell^+ \ell^-$ process and the branching ratio of the $b\to s ν\barν$ process are also calculated.

hep-ph↗

arXiv1996

$b \to s l \bar l $ in the minimal supergravity model

The $b \rightarrow s l^+ l^-$ process is studied in the minimal supergravity model in detail. Taking account of the long distance contributions from the $c\overline{c}$ resonances, we calculate the branching ratio and the lepton forward-backward asymmetry in this model. We find that there is a strong correlation between the branching ratios of $b \rightarrow s γ$ and $b \rightarrow s l^+ l^-$ processes and that the interference effect can change the $b \rightarrow s l^+ l^-$ branching ratio in the off-resonance regions by up to $\pm 15%$ depending on the relative phase between the long and short distance contributions. Using various phenomenological constraints including the branching ratio of $b \rightarrow s γ$, we show that there are regions in the parameter space where the branching ratio of $b \rightarrow s l^+ l^-$ is enhanced by about 50% compared to the SM. We also show that the branching ratio of $b \rightarrow s ν{\overline ν}$ is reduced at most by 10% from the SM prediction.

hep-ph↗

arXiv1994

Charged Higgs Effects on Exclusive Semi-tauonic $\bbox{B}$ Decays

We study effects of charged Higgs boson exchange in the $B$ semileptonic decays $\bar B \rightarrow D^{(*)}τ\barν_τ$. Both branching ratio and $τ$ polarization are examined. We use the recent experimental data on semileptonic $B$ decays and the heavy quark effective theory in order to reduce theoretical uncertainty in the hadronic form factors. Theoretical uncertainty in the branching ratio is found to be rather small and that in the $τ$ polarization is almost negligible. Their measurements will give nontrivial constraints on the charged Higgs sector.

hep-ph↗