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.Comment: Prepared for the proceedings of Dark 2009:Seventh International Heidelberg Conference on Dark Matter in Astro and Particle Physic

Gravitino Dark Matter with Weak-Scale Right-Handed Sneutrino

We consider cosmological implications of supersymmetric models with right-handed (s)neutrinos where the neutrino masses are purely Dirac-type. We pay particular attention to the case where gravitino is the lightest superparticle while one of the right-handed sneutrinos is next-to-the-lightest superparticle. We study constraints from big-bang nuleosynthesis and show that the constraints could be relaxed compared to the case without right-handed sneutrinos. As a result, the gravitino-dark-matter scenario becomes viable with relatively large value of the gravitino mass. We also discuss constraints from the structure formation; in our model, the free-streaming length of the gravitino dark matter may be as long as O(1 Mpc), which is comparable to the present observational upper bound on the scale of free-streaming.Comment: 18 pages, 6 figure

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.Comment: 20 pages, 6 figure

Testing the Littlest Higgs Model with T-parity at the Large Hadron Collider

In the framework of the littlest Higgs model with T-parity (LHT), we study the production processes of T-even (T_+) and T-odd (T_-) partners of the top quark at the Large Hadron Collider (LHC). We show that the signal events can be distinguished from the standard-model backgrounds, and that information about mass and mixing parameters of the top partners can be measured with relatively good accuracies. With the measurements of these parameters, we show that a non-trivial test of the LHT can be performed. We also discuss a possibility to reconstruct the thermal relic density of the lightest T-odd particle A_H using the LHC results, and show that the scenario where A_H becomes dark matter may be checked.Comment: 26 pages, 6 figure