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Takashi Shimomura

Publications and source records attributed to Takashi Shimomura.

At least 55 records · Page 3Linked to original sources
arXiv2016

MeV scale leptonic force for cosmic neutrino spectrum and muon anomalous magnetic moment

Characteristic patterns of cosmic neutrino spectrum reported by the IceCube collaboration and long-standing inconsistency between theory and experiment in muon anomalous magnetic moment are simultaneously explained by an extra leptonic force mediated by a gauge field with a mass of the MeV scale. With different assumptions for redshift distribution of cosmic neutrino sources, diffuse neutrino flux is calculated with the scattering between cosmic neutrino and cosmic neutrino background through the new leptonic force. Our analysis sheds light on a relation among lepton physics at the three different scales, PeV, MeV, and eV, and provides possible clues to the distribution of sources of cosmic neutrino and also to neutrino mass spectrum.

hep-ph↗
arXiv2016

Phenomenology of NMSSM in TeV scale mirage mediation

We study the next-to-minimal supersymmetric standard model (NMSSM) with the TeV scale mirage mediation, which is known as a solution for the little hierarchy problem in supersymmetry. Our previous study showed that 125 GeV Higgs boson is realized with O(10) % fine-tuning for 1.5 TeV gluino (1 TeV stop) mass. The $μ$ term could be as large as 500 GeV without sacrificing the fine-tuning thanks to a cancellation mechanism. The singlet-doublet mixing is suppressed by $\tanβ$. In this paper, we further extend this analysis. We argue that approximate scale symmetries play a role behind the suppression of the singlet-doublet mixing. They reduce the mixing matrix to a simple form that is useful to understand the results of the numerical analysis. We perform a comprehensive analysis of the fine-tuning including the singlet sector by introducing a simple formula for the fine-tuning measure. This shows that the singlet mass of the least fine-tuning is favored by the LEP anomaly for moderate $\tanβ$. We also discuss prospects for the precision measurements of the Higgs couplings at LHC and ILC and direct/indirect dark matter searches in the model.

hep-ph↗
arXiv2015

Combinatorial embedding of chain transitive zero-dimensional systems into chaos

We show that a zero-dimensional chain transitive dynamical system can be embedded into a densely uniformly chaotic system, with dense uniformly chaotic set $K$. We concretely construct a Mycielski set $K$ that is also invariant. Furthermore, every point in $K$ is positively and negatively transitive. The uniform proximality and recurrence of $K$ are also bidirectional.

math.DS↗
arXiv2015

Aperiodic homeomorphisms approximate chain mixing endomorphisms on the Cantor set

Let $f$ be a chain mixing continuous onto mapping from the Cantor set onto itself.Let $g$ be an aperiodic homeomorphism on the Cantor set. We show that homeomorphisms that are topologically conjugate to g approximate $f$ in the topology of uniform convergence if a trivial necessary condition on periodic points is satisfied.In particular, let $f$ be a chain mixing continuous onto mapping from the Cantor set onto itself with a fixed point and g, an aperiodic homeomorphism on the Cantor set. Then, homeomorphisms that are topologically conjugate to $g$ approximate $f$.

math.DS↗
arXiv2015

Non-homeomorphic topological rank and expansiveness

Downarowicz and Maass (2008) have shown that every Cantor minimal homeomorphism with finite topological rank $K > 1$ is expansive. Bezuglyi, Kwiatkowski and Medynets (2009) extended the result to non-minimal cases. On the other hand, Gambaudo and Martens (2006) had expressed all Cantor minimal continuou surjections as the inverse limit of graph coverings. In this paper, we define a topological rank for every Cantor minimal continuous surjection, and show that every Cantor minimal continuous surjection of finite topological rank has the natural extension that is expansive.

math.DS↗
arXiv2015

Chain mixing endomorphisms are approximated by subshifts on the Cantor set

Let f be a chain mixing continuous onto mapping from the Cantor set onto itself. Let g be a homeomorphism on the Cantor set that is topologically conjugate to a subshift. Then, homeomorphisms that are topologically conjugate to g approximate f in the topology of uniform convergence if a trivial necessary condition on the periodic points holds. In particular, if f is a chain mixing continuous onto mapping from the Cantor set onto itself with a fixed point, then homeomorphisms on the Cantor set that are topologically conjugate to a subshift approximate f in the topology of uniform convergence. In addition, homeomorphisms on the Cantor set that are topologically conjugate to a subshift without periodic points approximate any chain mixing continuous onto mappings from the Cantor set onto itself. In particular, let f be a homeomorphism on the Cantor set that is topologically conjugate to a full shift. Let g be a homeomorphism on the Cantor set that is topologically conjugate to a subshift. Then, a sequence of homeomorphisms that is topologically conjugate to g approximates f.

math.DS↗
arXiv2015

Graph covers and ergodicity for 0-dimensional systems

Bratteli--Vershik systems have been widely studied. In the context of general 0-dimensional systems, Bratteli--Vershik systems are homeomorphisms that have Kakutani--Rohlin refinements. Bratteli diagram has a strong power to analyze such systems. Besides this approach, general graph covers can be used to represent any 0-dimensional system. Indeed, all 0-dimensional systems can be described as a certain kind of sequences of graph covers that may not be brought about by the Kakutani--Rohlin partitions. In this paper, we follow the context of general graph covers to analyze the relations between ergodic measures and circuits of graph covers. First, we formalize the condition for a sequence of graph covers to represent minimal Cantor systems. In constructing invariant measures, we deal with general compact metrizable 0-dimensional systems. In the context of Bratteli diagrams with finite rank, it has previously been mentioned that all ergodic measures should be limits of some combinations of towers of Kakutani--Rohlin refinements. We demonstrate this for general 0-dimensional case, and develop a theorem that expresses the coincidence of the time average and the space average for ergodic measures. Additionally, we formulate a theorem that signifies the old relation between uniform convergence and unique ergodicity in the context of graph circuits for general 0-dimensional systems. Unlike previous studies, in our case of general graph covers, there arise a possibility of linear dependence of circuits. We give a condition for a full circuit system to be linearly independent. Previous researches also showed that the bounded combinatorics imply unique ergodicity. We present a lemma that enables us to consider unbounded ranks of winding matrices.

math.DS↗
arXiv2014

Mind the gap on Icecube: Cosmic neutrino spectrum and muon anomalous magnetic moment in the gauged L_μ - L_τ model

The energy spectrum of cosmic neutrinos, which was recently reported by the IceCube collaboration, shows a gap between 400 TeV and 1 PeV. An unknown neutrino interaction mediated by a field with a mass of the MeV scale is one of the possible solutions to this gap. We examine if the leptonic gauge interaction L_μ - L_τ can simultaneously explain the two phenomena in the lepton sector: the gap in the cosmic neutrino spectrum and the unsettled disagreement in muon anomalous magnetic moment. We illustrate that there remains the regions in the model parameter space, which account for both the problems. Our results also provide a hint for the distance to the source of the high-energy cosmic neutrinos.

hep-ph↗
arXiv2014

Big-bang nucleosynthesis through bound-state effects with a long-lived slepton in the NMSSM

We show that the Li problems can be solved in the next-to-minimal supersymmetric standard model where the slepton as the next-to-lightest SUSY particle is very long-lived. Such a long-lived slepton induces exotic nuclear reactions in big-bang nucleosynthesis, and destroys and produces the $^7$Li and $^6$Li nuclei via bound state formation. We study cases where the lightest SUSY particle is singlino-like neutralino and bino-like neutralino to present allowed regions in the parameter space which is consistent with the observations on the dark matter and the Higgs mass.

hep-ph↗
arXiv2013

A first evidence of the CMSSM is appearing soon

We explore the coannihilation region of the constrained minimal supersymmetric standard model (CMSSM) being consistent with current experimental/observational results. The requirements from the experimental/observational results are the 125GeV Higgs mass and the relic abundances of both the dark matter and light elements, especially the lithium-7. We put these requirements on the caluculated values, and thus we obtain allowed region. Then we give predictions to the mass spectra of the SUSY particles, the anomalous magnetic moment of muon, branching fractions of the B-meson rare decays, the direct detection of the neutralino dark matter, and the number of SUSY particles produced in 14TeV run at the LHC experiment. Comparing these predictions with current bounds, we show the feasibility of the test for this scenario in near future experiment.

hep-ph↗
arXiv2012

Neutrino Mass and Proton Decay in a ${U(1)}_R$ Symmetric Model

We study a ${U(1)}_R$ symmetric extenstion of supersymmetric standard model with supersymmetry breaking in the visible as well as hidden sectors. Specifically we study ${U(1)}_R$ breaking effects parametrized by the gravitino mass. A special $R$-charge assignment of right-handed neutrinos allows us to have neutrino Yukawa couplings with the $R$-charged Higgs field, which develops a tiny vacuum expectation value after the inclusion of $U(1)_R$ symmetry breaking. Even with O(1) Yukawa couplings, a suitable size of Dirac neutrino masses can be generated if the gravitino mass is very small, $m_{3/2}=1\hbox{---}10\,\mathrm{eV}$. Our flipped $R$-charge assignment also allows a new type of dimension five operator that can induce the proton decay. It turns out that the proton stability mildly constrains the allowed range of the gravitino mass: Gravitino heavier than $10 \ \mathrm{keV}$ can evade the proton decay constraint as well as cosmological ones. In this case, the largest neutrino Yukawa coupling is comparable to the electron Yukawa. We also calculate the mass of the pseudo goldsino and its mixing to neutralinos, and briefly discuss its implications in cosmology and Higgs phenomenology.

hep-ph↗
arXiv2012

TeV scale mirage mediation in NMSSM

We study the next-to-minimal supersymmetric standard model. We consider soft supersymmetry breaking parameters, which are induced by the mirage mediation mechanism of supersymmetry breaking. We concentrate on the mirage mediation, where the so-called mirage scale is the TeV scale. In this scenario, we can realize the up-type Higgs soft mass of O(200) GeV, while other masses such as gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation between the effective μ-term and the down-type Higgs soft mass ameliorates the fine-tuning in the electroweak symmetry breaking even for μ=O(500) GeV. The mixing between the doublet and singlet Higgs bosons is suppressed by (λ/κ)/tanβ. Then the lightest doublet Higgs mass naturally reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino are light and their linear combination is the lightest superparticle.

hep-ph↗
arXiv2012

Allowed slepton intergenerational mixing in light of light element abundances

We studied allowed region on the intergenerational mixing parameters of sleptons from a viewpoint of big-bang nucleosynthesis in a slepton-neutralino coannihilation scenario. In this scenario, $^7$Li and $^6$Li problems can be solved by considering exotic reactions caused by bound-state effects with a long-lived slepton. Light element abundances are calculated as functions of the relic density and lifetime of the slepton which considerably depend on the intergenerational mixing parameters. Compared with observational light element abundances, we obtain allowed regions on the intergenerational mixing. Ratio of selectron component to stau component, $c_e$, is allowed in $2\times 10^{-11} \lesssim c_e \lesssim 2\times 10^{-9}$ with solving both the $^7$Li and $^6$Li problems. Similarly, the ratio for smuon, $c_μ$, is allowed in $%2\times 10^{-7} \lesssim c_μ \lesssim 5\times 10^{-5}$ for mass difference between slepton and neutralino, which is smaller than muon mass, and $ %10^{-11}\lesssim c_μ \lesssim 2\times 10^{-10}$ for the mass difference in range between muon mass and 125 MeV. We also discuss collider signatures of the slepton decays. We find characteristic double peaks in momentum distribution of event number of the slepton decays with allowed mixing parameters. Discoveries of the double peaks at future collider experiments should confirm our scenario.

hep-ph↗
arXiv2012

Constraining the Higgs sector from False Vacua in the Next-to-Minimal Supersymmetric Standard Model

We study the mass, the mixing and the coupling with $Z$ boson of the lightest Higgs boson in the next-to-minimal supersymmetric standard model. The vacuum structure of the Higgs potential is analyzed and the new false vacua are discussed. The significant parameter region can be excluded by requiring that the realistic vacuum is deeper than false vacua, which result in constraints on the properties of the lightest Higgs boson.

hep-ph↗
arXiv2011

Masses of dark matter and neutrino from TeV scale spontaneous $U(1)_{B-L}$ breaking

We propose a simple testable model with mass generation mechanisms for dark matter and neutrino based on the gauged $U(1)_{B-L}$ symmetry and an exact $Z_2$ parity. The $U(1)_{B-L}$ symmetry is spontaneously broken at the TeV scale, by which $Z_2$-odd right-handed neutrinos receive Majorana masses of the electroweak scale. The lightest one is a dark matter candidate, whose stability is guaranteed by the $Z_2$ parity. Resulting lepton number violation is transmitted to the left-handed neutrinos $ν_L^i$ via the loop-induced dimension-six operator. Consequently, the tiny masses of $ν_L^i$ can be generated without excessive fine tuning. The observed dark matter abundance can be reproduced by the pair annihilation via the s-channel scalar exchange due to mixing of neutral components of $Φ$ and $S$, where $Φ$ and $S$ respectively represent the Higgs doublet and the additional scalar singlet with the $B-L$ charge. The model can be tested at collider experiments as well as flavor experiments through the discriminative predictions such as two light neutral Higgs bosons with large mixing, invisible decays of the Higgs bosons as well as the $B-L$ gauge boson, and lepton flavor violation.

hep-ph↗
arXiv2011

Constraints from Color and/or Charge Breaking Minima in the $ν$SSM

We consider a model where right-handed neutrinos and sneutrinos are introduced to the minimal supersymmetric standard model. In the scalar potential of this model, there exist trilinear and quartic terms in scalar potential that are proportional to Yukawa couplings of neutrinos. Due to these trilinear and quartic terms, Color and/or Charge Breaking (CCB) and Unbounded-From-Below (UFB) directions appear along which sneutrinos have a vacuum expectation value, making the vacuum of the electroweak symmetry breaking unstable. We analyze scalar potential of this model and derive necessary conditions for CCB and UFB directions to vanish.

hep-ph↗
arXiv2011

Constraints from Unrealistic Vacua in the Next-to-Minimal Supersymmetric Standard Model

We study constraints to avoid deep unrealistic minima in the next-to-minimal supersymmetric standard model. We analyze a scalar potential along directions where all of and one of the three Higgs fields develop their vacuum expectation values, and find unrealistic minima deeper than the electroweak symmetry breaking (EWSB) vacuum. These unrealistic minima threaten the realization of the successful EWSB and therefore should be avoided. Necessary conditions to avoid these minima result in constraints of parameters. We show that a wide and significant region of the parameter space, especially large λ, is ruled out by our constraints.

hep-ph↗