arXiv subjects

Shigeki Matsumoto

Publications and source records attributed to Shigeki Matsumoto.

At least 109 records · Page 6Linked to original sources

arXiv2010

Can WIMP Dark Matter overcome the Nightmare Scenario?

Even if new physics beyond the Standard Model (SM) indeed exists, the energy scale of new physics might be beyond the reach at the Large Hadron Collider (LHC) and the LHC could find only the Higgs boson but nothing else. This is the so-called "nightmare scenario". On the other hand, the existence of the dark matter has been established from various observations. One of the promising candidates for thermal relic dark matter is a stable and electric charge-neutral Weakly Interacting Massive Particle (WIMP) with the mass below the TeV scale. In the nightmare scenario, we introduce a WIMP dark matter singlet under the SM gauge group, which only couples to the Higgs doublet at the lowest order, and investigate a possibility that such WIMP dark matter can be a clue to overcome the nightmare scenario via various phenomenological tests such as the dark matter relic abundance, the direct detection experiments for the dark matter particle, and the production of the dark matter particle at the LHC.

hep-ph↗

arXiv2009

Cosmic Gamma-ray from Inverse Compton Process in Unstable Dark Matter Scenario

Motivated by the PAMELA anomaly in the fluxes of cosmic-ray positron and electron, we study the cosmic gamma-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the positron and electron emission by the decay of dark matter. We calculate the fluxes of IC-induced gamma-ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. We discuss a possibility that large dark matter mass over TeV scale might be constrained by the gamma-ray observation by Fermi Gamma-ray Space Telescope.

hep-ph↗

arXiv2009

Productions of second Kaluza-Klein gauge bosons in the minimal universal extra dimension model at LHC

We calculate the production rates of the second Kaluza-Klein (KK) photon $γ^{(2)}$ and Z boson $Z^{(2)}$ at the LHC including all significant processes in the minimal Universal Extra Dimension (MUED) model. For discrimination of the MUED model from other TeV scale models at the LHC, $γ^{(2)}$ and $Z^{(2)}$ play a crucial role. In order to discuss the discrimination and calculate their production rates, we derive KK number violating operators including the contribution of the top Yukawa coupling. Using these operators, we accurately calculate branching ratios of second KK particles. In addition we find that these KK number violating operators provide new processes for $γ^{(2)}$ and $Z^{(2)}$ productions, such as cascade decay from second KK quarks produced through these operators. They have large contributions to their total production rates. In particular, these production processes give the dominant contribution for $γ^{(2)}$ production for $1/R \gtrsim 800$ GeV. As a result, with an integrated luminosity of 100 fb$^{-1}$, the number of produced $γ^{(2)}$ and $Z^{(2)}$ are estimated as 10$^6$ - 10$^2$ for the compactification scale between 400 GeV and 2000 GeV.

hep-ph↗

arXiv2009

Gauge-Higgs Dark Matter

When the anti-periodic boundary condition is imposed for a bulk field in extradimensional theories, independently of the background metric, the lightest component in the anti-periodic field becomes stable and hence a good candidate for the dark matter in the effective 4D theory due to the remaining accidental discrete symmetry. Noting that in the gauge-Higgs unification scenario, introduction of anti-periodic fermions is well-motivated by a phenomenological reason, we investigate dark matter physics in the scenario. As an example, we consider a five-dimensional SO(5)$\timesU(1)_X$ gauge-Higgs unification model compactified on the $S^1/Z_2$ with the warped metric. Due to the structure of the gauge-Higgs unification, interactions between the dark matter particle and the Standard Model particles are largely controlled by the gauge symmetry, and hence the model has a strong predictive power for the dark matter physics. Evaluating the dark matter relic abundance, we identify a parameter region consistent with the current observations. Furthermore, we calculate the elastic scattering cross section between the dark matter particle and nucleon and find that a part of the parameter region is already excluded by the current experimental results for the direct dark matter search and most of the region will be explored in future experiments.

hep-ph↗

arXiv2009

Measurement of Heavy Gauge Bosons in Little Higgs Model with T-parity at ILC

The Littlest Higgs Model with T-parity is one of the attractive candidates of physics beyond the Standard Model. One of the important predictions of the model is the existence of new heavy gauge bosons, where they acquire mass terms through the breaking of global symmetry necessarily imposed on the model. The determination of the masses are, hence, quite important to test the model. In this paper, the measurement accuracy of the heavy gauge bosons at ILC is eported.

hep-ph↗

arXiv2009

Precision Measurements of the model parameters in the Littlest Higgs model with T-parity

We investigate a possibility of precision measurements for parameters of the Littlest Higgs model with T-parity at the International Linear Collider (ILC). The model predicts new gauge bosons which masses strongly depend on the vacuum expectation value that breaks a global symmetry of the model. Through Monte Carlo simulations of production processes of new gauge bosons, we show that these masses can be determined very accurately at the ILC for a representative parameter point of the model. From the simulation result, we also discuss the determination of other model parameters at the ILC.

hep-ph↗

arXiv2009

Cosmic Gamma-ray from Inverse Compton Process in Unstable Dark Matter Scenario

Motivated by the PAMELA anomaly in the fluxes of cosmic-ray electron and positron, we study the cosmic gamma-ray induced by the inverse Compton (IC) scattering process in unstable dark matter scenario assuming that the anomaly is due to the electron and positron emission by the decay of dark matter. We calculate the fluxes of IC-induced gamma-ray produced in our Galaxy and that from cosmological distance, and show that both of them are significant. If the gamma-ray flux is precisely determined by Fermi Gamma-ray Space Telescope for various line-of-sight directions, it will provide an important test of the decaying dark matter scenario.

astro-ph.CO↗

arXiv2009

High Energy Cosmic Rays from Decaying Supersymmetric Dark Matter

Motivated by the recent PAMELA and ATIC results, we calculate the electron and positron fluxes from the decay of lightest-superparticle (LSP) dark matter. We assume that the LSP is the dominant component of dark matter, and consider the case that the R-parity is very weakly violated so that the lifetime of the LSP becomes of the order of 10^26 sec. We will see that, with such a choice of the lifetime, the cosmic-ray electron and positron from the decay can be the source of the anomalous electron and positron fluxes observed by PAMELA and ATIC. We consider the possibilities that the LSP is the gravitino, the lightest neutralino, and scalar neutrino, and discuss how the resultant fluxes depend on the dark-matter model. We also discuss the fluxes of gamma-ray and anti-proton, and show that those fluxes can be consistent with the observed value in the parameter region where the PAMELA and ATIC anomalies are explained.

hep-ph↗

arXiv2009

Cosmic-Ray Positron from Superparticle Dark Matter and the PAMELA Anomaly

Motivated by the anomalous positron flux recently reported by the PAMELA collaboration, we study the cosmic-ray positron produced by the pair annihilation and the decay of superparticle dark matter. We calculate the cosmic-ray positron flux and discuss implications of the PAMELA data. We show that the positron excess observed by the PAMELA can be explained with some of the superparticle dark matter.

hep-ph↗

arXiv2009

Precision Measurements of Little Higgs Parameters at the International Linear Collider

We investigate a possibility of precision measurements for parameters of the Littlest Higgs model with T-parity at the International Linear Collider (ILC). The model predicts new gauge bosons (AH, ZH, and WH), among which the heavy photon (AH) is a candidate for dark matter. The masses of these new gauge bosons strongly depend on the vacuum expectation value that breaks a global symmetry of the model. Through Monte Carlo simulations of the processes: e+ e- ->AH ZH and e+ e- -> WH+ WH-, we show how precisely the masses can be determined at the ILC for a representative parameter point of the model. We also discuss the determination of the Little Higgs parameters and its impact on the future measurement of the thermal abundance of the dark matter relics in our universe.

hep-ph↗

arXiv2009

Production Rate of Second KK Gauge Bosons in UED Models at LHC

We calculate the production rates of the second Kaluza-Klein (KK) photon $γ^{(2)}$ and Z boson $Z^{(2)}$ at the LHC including all significant processes in the minimal universal extra dimension (MUED) model. For discrimination of the MUED model from other TeV scale models in hadron collider experiments, $γ^{(2)}$ and $Z^{(2)}$ play a crucial role. In order to discuss the discrimination and calculate their production rates, we derive effective Lagrangian containing KK number violating operators. We show that KK number violating processes are extremely important for the compactification scale larger than 800 GeV. We find that, with an integrated luminosity of 100 fb$^{-1}$, $γ^{(2)}$ and $Z^{(2)}$ are produced 10$^6$ - 10$^2$ for the compactification scale between 400 GeV and 2000 GeV.

hep-ph↗

arXiv2009

PAMELA and ATIC Anomalies in Decaying Gravitino Dark Matter Scenario

Motivated by the recent results from the PAMELA and ATIC, we study the cosmic-ray electron and positron produced by the decay of gravitino dark matter. We calculate the cosmic-ray electron and positron fluxes and discuss implications to the PAMELA and ATIC data. In this paper, we will show that the observed anomalous fluxes by the PAMELA and ATIC can be explained in such a scenario. We will also discuss the synchrotron radiation flux from the Galactic center in such a scenario.

hep-ph↗

arXiv2009

How accurately is the property of the Little Higgs Dark Matter determined at the ILC?

Little Higgs scenario provides us a new solution for the hierarchy problem of the Standard Model. The Littlest Higgs model with T-parity, which is one of models in the scenario, solves the dark matter problem in our universe. In this talk, we discuss how accurately the property of the dark matter is determined at linear collides. We also mention how precisely does the thermal abundance of the dark matter determined at the 500 GeV and 1 TeV collides, and compare the results with those at the LHC.

hep-ph↗

arXiv2009

Measurements of the model parameter in the littlest Higgs model with T-parity

In the Littlest Higgs model with T-parity, we study production processes of new gauge bosons at the international linear collider (ILC). Through Monte Carlo simulations of the production processes, we show that the heavy gauge boson masses can be determined very accurately at the ILC for a representative parameter point of the model. From the simulation result, we also discuss the determination of other model parameters at the ILC.

hep-ph↗

arXiv2009

Simulation study of ZHAH mode in Littlest Higgs Model with T-Parity

We investigate a possibility to measure parameters of the Littlest Higgs model with T-parity at the ILC with sqrt(s) = 500 GeV. The model predicts new gauge bosons (AH, ZH, and WH), among which the heavy photon (AH) is a candidate for dark matter. Through Monte Carlo simulations of the process of e+ e- -> AH ZH, we show that the masses can be determined with accuracies of 16.2% for m_AH and 4.3% for m_ZH. In additionally, the vacuum expectation value can be determined with accuracies of 4.3%.

hep-ph↗

arXiv2009

Observable Seesaw and its Collider Signatures

We discuss the scenario with TeV-scale right-handed neutrinos, which are accessible at future colliders, while holding down tiny seesaw-induced masses and sizable couplings to the standard-model particles. The signal with tri-lepton final states and large missing transverse energy is appropriate for studying collider signatures of the scenario with extra spatial dimensions. We show that the LHC experiment generally has a potential to discover the signs of extra dimensions and the origin of small neutrino masses.

hep-ph↗

arXiv2008

Synchrotron Radiation from the Galactic Center in Decaying Dark Matter Scenario

We discuss the synchrotron radiation flux from the Galactic center in unstable dark matter scenario. Motivated by the anomalous excess of the positron fraction recently reported by the PAMELA collaboration, we consider the case that the dark matter particle is unstable (and long-lived), and that energetic electron and positron are produced by the decay of dark matter. Then, the emitted electron and positron becomes the source of the synchrotron radiation. We calculate the synchrotron radiation flux for models of decaying dark matter, which can explain the PAMELA positron excess. Taking the lifetime of the dark matter of O(10^26 sec), which is the suggested value to explain the PAMELA anomaly, the synchrotron radiation flux is found to be O(1 kJy/str) or smaller, depending on the particle-physics and cosmological parameters.

astro-ph↗

arXiv2008

Universal Extra Dimension models with right-handed neutrinos

Relic abundance of dark matter is investigated in the framework of universal extra dimension (UED) models with right-handed neutrinos. These models are free from the KK graviton problem in the minimal UED model. The first KK particle of the right-handed neutrino is a dark matter candidate in this framework. When ordinary neutrino masses are large enough such as the degenerate mass spectrum case, the dark matter relic abundance can increase significantly. The scale of the extra dimension consistent with cosmological observations can be 500 GeV in the minimal setup of UED models with right-handed neutrinos.

hep-ph↗