Numerical Simulation of Radio Signal from Extended Air Showers

The burst of radio emission by the extensive air shower provides a promising alternative for detecting ultra-high energy cosmic rays.We have developed an independent numerical program to simulate these radio signals. Our code is based on a microscopic treatment, with both the geosynchrotron radiation and charge excess effect included. Here we make a first presentation of our basic program and its results. The time signal for different polarizations are computed, we find that the pulses take on a bipolar pattern, the spectrum is suppressed towards the lower frequencies.We investigate how the shower at different heights in atmosphere contribute to the total signal, and examine the signal strength and distribution at sites of different elevations. We also study the signal from showers of different inclination angles and azimuth directions. In all these cases we find the charge excess effect important.Comment: 23 pages, 14 figure

Particle decays during the cosmic dark ages

We consider particle decays during the cosmic dark ages with two aims: (1) to explain the high optical depth reported by the Wilkinson Microwave Anisotropy Probe (WMAP), and (2) to provide new constraints to the parameter space for decaying particles. We delineate the decay channels in which most of the decay energy ionizes and heats the intergalactic medium gas [and thus affects the cosmic microwave background (CMB)], and those in which most of the energy is carried away—e.g. photons with energies 100 keV<~E<~1 TeV—and thus appears as a contribution to diffuse x-ray and gamma-ray backgrounds. The new constraints to the decay-particle parameters from the CMB power spectrum thus complement those from the cosmic x-ray and gamma-ray backgrounds. Although decaying particles can indeed produce an optical depth consistent with that reported by WMAP, in so doing they produce new fluctuations in the CMB temperature and polarization power spectra. For decay lifetimes less than the age of the Universe, the induced power spectra generally violate current constraints, while the power spectra are usually consistent if the lifetime is longer than the age of the Universe

Three-Body Annihilation of Neutralinos Below Two-Body Thresholds

We calculate the cross section for s-wave neutralino annihilation to three-body final states below the W^+ W^- and t-bar t thresholds. Such three-body channels may dominate the annihilation cross section if the neutralino mass is not too much less than m_t and m_W respectively. Furthermore, because neutrinos produced in these channels are much more energetic than those from the $b\bar{b}$ or tau^+ tau^- channels, they can dominate the energetic-neutrino fluxes from neutralino annihilation in the Sun or Earth far below these thresholds and significantly enhance the neutrino signal in certain regions of the supersymmetric parameter space.Comment: 19 pages, 8 postscript figures, use JHEP.cl

Relic Abundance of Asymmetric Dark Matter in Quintessence

We investigate the relic abundance of asymmetric Dark Matter particles in quintessence model with a kination phase. The analytic calculation of the asymmetric Dark Matter in the standard cosmological scenario is extended to the nonstandard cosmological scenario where we specifically discuss the quintessence model with a kination phase. We found that the enhancement of Hubble rate changes the relic density of particles and anti--particles. We use the present day Dark Matter abundance to constrain the Hubble rate in quintessence model with a kination phase for asymmetric Dark Matter.Comment: 13 pages, 9 figure