arXiv subjects

Motoi Endo

Publications and source records attributed to Motoi Endo.

At least 55 records · Page 3Linked to original sources

arXiv2016

Chargino contributions in light of recent $ε'/ε$

Recently, the standard model prediction of $ε'/ε$ was improved, and a discrepancy from the experimental results was reported at the $2.9σ$ level. We study the chargino contributions to $Z$ penguin especially with the vacuum stability constraint. The vacuum decay rate is investigated, and it is shown that the discrepancy can be explained if superparticles are lighter than 4-6 TeV. Correlations with $\mathcal{B}(K_L\toπ^0ν\barν)$ and other experimental constraints are also discussed.

hep-ph↗

arXiv2016

ATLAS on-Z Excess Through Vector-Like Quarks

We investigate the possibility that the excess observed in the leptonic-$Z +$jets $+\slashed{E}_T$ ATLAS SUSY search is due to pair productions of a vector-like quark $U$ decaying to the first-generation quarks and $Z$ boson. We find that the excess can be explained within the 2$σ$ (up to 1.4$σ$) level while evading the constraints from the other LHC searches. The preferred range of the mass and branching ratio are $610 < m_{U} < 760$ GeV and ${\rm Br}(U \rightarrow Z q) > 0.3$-$0.45$, respectively.

hep-ph↗

arXiv2016

Diphoton Excess and Running Couplings

The recently observed diphoton excess at the LHC may suggest the existence of a singlet (pseudo-) scalar particle with a mass of 750 GeV which couples to gluons and photons. Assuming that the couplings to gluons and photons originate from loops of fermions and/or scalars charged under the Standard Model gauge groups, we show that here is a model-independent upper bound on the cross section $σ(pp\to S\to γγ)$ as a function of the cutoff scale $Λ$ and masses of the fermions and scalars in the loop. Such a bound comes from the fact that the contribution of each particle to the diphoton event amplitude is proportional to its contribution to the one-loop $β$ functions of the gauge couplings. We also investigate the perturbativity of running Yukawa couplings in models with fermion loops, and show the upper bounds on $σ(pp\to S\to γγ)$ for explicit models.

hep-ph↗

arXiv2015

Renormalization-Scale Uncertainty in the Decay Rate of False Vacuum

We study radiative corrections to the decay rate of false vacua, paying particular attention to the renormalization-scale dependence of the decay rate. The decay rate exponentially depends on the bounce action. The bounce action itself is renormalization scale dependent. To make the decay rate scale-independent, radiative corrections, which are due to the field fluctuations around the bounce, have to be included. We show quantitatively that the inclusion of the fluctuations suppresses the scale dependence, and hence is important for the precise calculation of the decay rate. We also apply our analysis to a supersymmetric model and show that the radiative corrections are important for the Higgs-stau system with charge breaking minima.

hep-ph↗

arXiv2015

Footprints of Supersymmetry on Higgs Decay

Motivated by future collider proposals that aim to measure the Higgs properties precisely, we study the partial decay widths of the lightest Higgs boson in the minimal supersymmetric standard model with an emphasis on the parameter region where all superparticles and heavy Higgs bosons are not accessible at the LHC. Taking account of phenomenological constraints such as the Higgs mass, flavor constraints, vacuum stability, and perturbativity of coupling constants up to the grand unification scale, we discuss how large the deviations of the partial decay widths from the standard model predictions can be. These constraints exclude large fraction of the parameter region where the Higgs widths show significant deviation from the standard model predictions. Nevertheless, even if superparticles and the heavy Higgses are out of the reach of 14TeV LHC, the deviation may be large enough to be observed at future $e^+e^-$ collider experiments.

hep-ph↗

arXiv2014

Reconstruction of Vector-like Top Partner from Fully Hadronic Final States

We investigate the potential to search for the vector-like top partner in fully hadronic final states at the LHC. An algorithm is developed that kinematically reconstructs the vector-like top. We show that for moderate masses and a large branching fraction into the top quark and Higgs boson, the reconstruction works with good quality.

hep-ph↗

arXiv2014

Heavy WIMP through Higgs portal at the LHC

LHC constraints on Higgs-portal WIMPs are studied. Scalar, vector and anti-symmetric tensor fields are considered. They are assumed to be heavier than a half of the Higgs boson mass. We investigate 8 TeV LHC results on signatures of the vector boson fusion, mono-jet and associated production of the $Z$ boson, which proceed via virtual exchange of the Higgs boson. We show that Higgs-portal interactions of the vector and tensor WIMPs are constrained to be less than 0.43 and 0.16, respectively, while those for the scalar are very weak. Prospects of the 14 TeV LHC are also discussed.

hep-ph↗

arXiv2014

Unitarity Bounds on Dark Matter Effective Interactions at LHC

The perturbative unitarity bound is studied in the monojet process at LHC. The production of the dark matter is described by the low-energy effective theory. The analysis of the dark matter signal is not validated, if the unitarity condition is violated. It is shown that the current LHC analysis the effective theory breaks down, at least, when the dark matter is lighter than O(100) GeV. Future prospects for $\sqrt{s}$ = 14 TeV are also discussed. The result is independent of physics in high energy scales.

hep-ph↗

arXiv2014

Lepton Universality Test of Extra Leptons using Hadron Decay

We study the flavor universality of the lepton couplings with the W and Z bosons. Currently, it is constrained by the electroweak precision observables. We focus on the leptonic decay of the pion. It is shown that the decay is expected to have a comparable or better sensitivity to the lepton-flavor universality in the near future. Furthermore, it provides a complementary information in determining the Wlnu couplings without assuming new physics models. This result is applied to a model of the extra lepton.

hep-ph↗

arXiv2014

Future Prospects for Stau in Higgs Coupling to Di-photon

We study future prospects of the stau which contributes to the Higgs coupling to di-photon. The coupling is sensitive to new physics and planned to be measured at percent levels in future colliders. We show that, if the excess of the coupling is measured to be larger than 4 %, the lightest stau is predicted to be lighter than about 200 GeV by taking vacuum meta-stability conditions into account. Such a stau can be discovered at ILC. Moreover, we show how accurately the stau contribution to the coupling can be reconstructed from the information that is available at ILC. We also argue that, if the stau mixing angle is measured, the mass of the heaviest stau can be predicted by measuring the Higgs coupling, even when the heaviest stau is not yet discovered at the early stage of ILC.

hep-ph↗

arXiv2013

Reconstructing Supersymmetric Contribution to Muon Anomalous Magnetic Dipole Moment at ILC

We study the possibility to determine the supersymmetric (SUSY) contribution to the muon anomalous magnetic dipole moment by using ILC measurements of the properties of superparticles. Assuming that the contribution is as large as the current discrepancy between the result of the Brookhaven E821 experiment and the standard-model prediction, we discuss how and how accurately the SUSY contribution can be reconstructed. We will show that, in a sample point, the reconstruction can be performed with the accuracy of ~ 13 % with the center-of-mass energy 500 GeV and the integrated luminosity ~ 500-1000 fb-1.

hep-ph↗

arXiv2013

Probing Bino Contribution to Muon g-2

We study SUSY models in which Bino contributions solve the muon g-2 anomaly. The contributions are enhanced by large left-right mixing of the smuons. However, it is constrained by the vacuum stability condition of the slepton--Higgs potential. Therefore, there are upper bounds on masses of sleptons and Bino. When the slepton soft masses are universal, the upper bound on the smuon mass becomes 330 (460)GeV in order to solve the g-2 anomaly at the 1 sigma (2 sigma) level. It is within the reach of LHC and ILC. If the stau is heavier than the smuon, the bound can be as large as 1.4 (1.9)TeV. Such non-universal slepton mass spectrum generically predicts too large LFV/CPV. We show that the models are expected to be probed by LHC/ILC and LFV/CPV complementarily in future.

hep-ph↗

arXiv2013

Axino dark matter with R-parity violation and 130 GeV gamma-ray line

We show that decaying axino dark matter with R-parity violation can explain the observed excess of the 130GeV gamma-ray line from the Galactic center in the Fermi data. The branching fraction of the axino decay into monochromatic photons can be O(1), and constraints from continuum gamma-rays and the anti-proton flux are ameliorated. The Peccei-Quinn scale of $O(10^{13}-10^{14})$\,GeV and the R-parity violation parameter of $O(10^{-12}-10^{-11})$ are cosmologically favored.

hep-ph↗

arXiv2013

Muon g-2 vs LHC in Supersymmetric Models

There is more than 3 sigma deviation between the experimental and theoretical results of the muon g-2. This suggests that some of the SUSY particles have a mass of order 100 GeV. We study searches for those particles at the LHC with particular attention to the muon g-2. In particular, the recent results on the searches for the non-colored SUSY particles are investigated in the parameter region where the muon g-2 is explained. The analysis is independent of details of the SUSY models. Future prospects of the collider searches are also discussed.

hep-ph↗

arXiv2012

Gauge Mediation Models with Vectorlike Matters at the LHC

Gauge mediation model with vectorlike matters (V-GMSB) is one of the few viable SUSY models that explains the 126 GeV Higgs boson mass and the muon anomalous magnetic moment simultaneously. We explore exclusion bounds on V-GMSB model from latest LHC SUSY searches.

hep-ph↗

arXiv2012

Constraints on Hidden Photon Models from Electron g-2 and Hydrogen Spectroscopy

The hidden photon model is one of the simplest models which can explain the anomaly of the muon anomalous magnetic moment (g-2). The experimental constraints are studied in detail, which come from the electron g-2 and the hydrogen transition frequencies. The input parameters are set carefully in order to take dark photon contributions into account and to prevent the analysis from being self-inconsistent. It is shown that the new analysis provides a constraint severer by more than one order of magnitude than the previous result.

hep-ph↗

arXiv2012

Scalar Decay into Gravitinos in the Presence of D-term SUSY Breaking

Scalar decay into gravitinos is studied in the presence of D-term supersymmetry (SUSY) breaking. The gravitinos produced by the decay of coherent oscillations of scalar fields, such as moduli and inflatons, cause cosmological problems. We show the general formula for the partial decay rate of the scalar into two gravitinos. Applying it to a concrete model of D-term SUSY breaking, we find that D-term SUSY breaking can suppress gravitino production.

hep-ph↗

arXiv2012

Mass Insertion Formula for Chargino Contribution to ΔB = 1 Wilson Coefficients and its Application to CP Asymmetries of B \to Kπ

The comprehensive mass insertion formula of the b \to s \bar q q transitions was provided for the chargino contributions. The method clarifies physics behind the calculations of the supersymmetric contributions to FCNCs. The result was applied to the analysis of the difference of the CP asymmetries of the B \to Kπdecays. It is shown that the supersymmetry is not responsible for the discrepancy.

hep-ph↗