Constraints on decaying dark matter from the extragalactic gamma-ray background

If dark matter is unstable and the mass is within GeV-TeV regime, its decays produce high-energy photons that give contribution to the extragalactic gamma-ray background (EGRB). We constrain dark matter decay by analyzing the 50-month EGRB data measured with Fermi satellite, for different decay channels motivated with several supersymmetric scenarios featuring R-parity violation. We adopt the latest astrophysical models for various source classes such as active galactic nuclei and star-forming galaxies, and take associated uncertainties properly into account. The lower limits for the lifetime are very stringent for a wide range of dark matter mass, excluding the lifetime shorter than 10^28 s for mass between a few hundred GeV and ~1TeV, e.g., for b\bar{b} decay channel. Furthermore, most dark matter models that explain the anomalous positron excess are also excluded. These constraints are robust, being little dependent on astrophysical uncertainties, unlike other probes such as Galactic positrons or anti-protons.Comment: 20 pages, 6 figures, published versio

Grand Unification and Subcritical Hybrid Inflation

We consider hybrid inflation for small couplings of the inflaton to matter such that the critical value of the inflaton field exceeds the Planck mass. It has recently been shown that inflation then continues at subcritical inflaton field values where quantum fluctuations generate an effective inflaton mass. The effective inflaton potential interpolates between a quadratic potential at small field values and a plateau at large field values. An analysis of the allowed parameter space leads to predictions for the scalar spectral index n_s and the tensor-to-scalar ratio r similar to those of natural inflation. Using the range for n_s and r favoured by the Planck data, we find that the energy scale of the plateau is constrained to the interval (1.6 - 2.4) * 10^16 GeV which includes the energy scale of gauge coupling unification in the supersymmetric standard model. The tensor-to-scalar ratio is predicted to have the lower bound r > 0.049 for 60 e-folds before the end of inflation.Comment: 5 pages, 3 figures, published version, a few typos are correcte

Fourth generation bound states

We investigate the spectrum and wave functions of q̅ ′q′ bound states for heavy fourth generation quarks (q′) that have a very small mixing with the three observed generations of standard model quarks. Such bound states come with different color, spin and flavor quantum numbers. Since the fourth generation Yukawa coupling, λ_q′, is large we include all perturbative corrections to the potential between the heavy quark and antiquark of order λ_(q′)^(2)N_c/16π^2 where N_c is the number of colors, as well as relativistic corrections suppressed by (v/c)^2. We find that the lightest fourth generation quark masses for which a bound state exists for color octet states. For the color singlet states, which always have a bound state, we analyze the influence that the Higgs couplings have on the size and binding energy of the bound states

Direct Detection of Dark Matter Degenerate with Colored Particles in Mass

In this Letter we explore the direct detection of the dark matter in the universe, assuming the dark matter particles are degenerate in mass with new colored particles below TeV scale. The scenario with such a mass spectrum is difficult to be confirmed or excluded by the present analysis at the LHC experiments because the QCD jets in the cascade decay of the new particles produced in the proton-proton collision are too soft to be triggered in the event selection. It is shown that both of the spin-independent and spin-dependent couplings of the dark matter with a nucleon are enhanced and the scattering cross section may reach even the current bound of the direct detection experiments. Then such a degenerate scenario may be tested in the direct detection experiments.Comment: 11 pages, 4 figures. Version accepted for publication in Phys. Lett.

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