Masaki Asano

Cosmic positron signature from dark matter in the littlest Higgs model with T-parity

We calculate the flux of cosmic positrons from the dark matter annihilation in the littlest Higgs model with T parity. The dark matter annihilates mainly into weak gauge bosons in the halo, and high-energy positrons are produced through leptonic and hadronic decays of the bosons. We investigate a possibility to detect the positron signal in upcoming experiments such as PAMELA and AMS-02. We found that the dark matter signal can be distinguished from the background in the PAMELA experiment when the dark matter mass is less than 120 GeV and the signal flux is enhanced due to a small scale clustering of dark matter. Furthermore, the signal from the dark matter annihilation can be detected in the AMS-02 experiment, even if such enhancement does not exist. We also discuss the invisible width of the Higgs boson in this model.

Natural Supersymmetry at the LHC

If the minimal supersymmetric standard model is the solution to the hierarchy problem, the scalar top quark (stop) and the Higgsino should weigh around the electroweak scale such as 200GeV. A low messenger scale, which results in a light gravitino, is also suggested to suppress the quantum corrections to the Higgs mass parameters. Therefore the minimal model for natural supersymmetry is a system with stop/Higgsino/gravitino whereas other superparticles are heavy. We study the LHC signatures of the minimal system and discuss the discovery potential and methods for the mass measurements.

Indirect dark matter searches as a probe of degenerate particle spectra

We consider the possibility that the cosmological dark matter consists of particles very close in mass to new colored particles below the TeV scale. While such a scenario is inherently dicult to directly conrm at colliders, we nd that indirect dark matter searches may be a powerful alternative. In particular, we show that in this case dark matter annihilation to qqg nal states can give rise to signicant antiproton (but also gamma-ray)

Natural supersymmetric spectrum in mirage mediation

The current results of LHC experiments exclude a large area of the light new particle region, namely, natural parameter space, in supersymmetric extension models. One of the possibilities for achieving the correct electroweak symmetry breaking naturally is the low-scale messenger scenario. Actually, the next-to-minimal supersymmetric standard model with TeV scale mirage mediation realizes the natural electroweak symmetry breaking with various mass spectra. In this paper, we show the possible mass spectrum in the scenario, e.g., the degenerate and/or hierarchical mass spectrum, and discuss these features.

Can R-parity violation hide vanilla supersymmetry at the LHC?

A bstractCurrent experimental constraints on a large parameter space in supersymmetric models rely on the large missing energy signature. This is usually provided by the lightest neutralino which stability is ensured by R-parity. However, if R-parity is violated, the lightest neutralino decays into the standard model particles and the missing energy cut is not efficient anymore. In particular, the U DD type R-parity violation induces the neutralino decay to three quarks which potentially leads to the most difficult signal to be searched at hadron colliders. In this paper, we study the constraints on R-parity violating supersymmetric models using a same-sign dilepton and a multijet signatures. We show that the gluino and squarks lighter than TeV are already excluded in the constrained minimal supersymmetric standard model with the R-parity violation if their masses are approximately equal. We also analyze constraints in a simplified model with the R-parity violation. We compare how the R-parity violation changes some of the observables typically used to distinguish a supersymmetric signal from standard model backgrounds.

Non-anomalous discrete R-symmetry, extra matters, and enhancement of the lightest SUSY Higgs mass

Abstract We consider low-energy supersymmetric model with non-anomalous discrete R -symmetry. To make the R -symmetry non-anomalous, we add new particles to the particle content of the minimal supersymmetric standard model (MSSM). Those new particles may couple to the Higgs boson, resulting in a significant enhancement of the lightest Higgs mass. We show that, in such a model, the lightest Higgs mass can be much larger than the MSSM upper bound; the lightest Higgs mass as large as 140 GeV (or larger) becomes possible.

130 GeV gamma-ray line and generic dark matter model building constraints from continuum gamma rays, radio, and antiproton data

An analysis of the Fermi gamma ray space telescope data has recently revealed a resolved gammaray feature close to the galactic center which is consistent with monochromatic photons at an energy of about 130 GeV. If interpreted in terms of dark matter (DM) annihilating into (Z, h), this would correspond to a DM particle mass of roughly 130GeV (145GeV, 155GeV). The rate for these loop-suppressed processes, however, is larger than typically expected for thermally produced DM. Correspondingly, one would generically expect even larger tree level production rates of standard model fermions or gauge bosons. Here, we quantify this expectation in a rather model-independent way by relating the tree level and loop amplitudes with the help of the optical theorem. As an application, we consider bounds from continuum gamma rays, radio and antiproton data on the tree level amplitudes and translate them into constraints on the loop amplitudes. We find that, independently of the DM production mechanism, any DM model aiming at explaining the line signal in terms of charged standard model particles running in the loop is in rather strong tension with at least one of these constraints, with the exception of loops dominated by top quarks. We stress that attempts to explain the 130GeV feature with internal bremsstrahlung do not suffer from such difficulties.

Precision Measurements of Little Higgs Parameters at the International Linear Collider

We investigate the possibility of precision measurements for parameters of the littlest Higgs model with

Neutralino dark matter in light Higgs boson scenario

T

Constraints on scalar phantoms

parity at the International Linear Collider. The model predicts new gauge bosons (