MG12 - Talk detail
 

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 Participant 

Institution

Session

Talk

Abstract

On the Propagation of Gravitational Waves across the Universe: Interaction with the Neutrino Component.

The stochastic background of primordial gravitational waves is a target for several experiments, spanning many orders of magnitude in frequency. At large wavelengths, it can be detected in the B-modes of the cosmic microwave background. At small scales, it is the target of detectors like LISA. Gravitational waves interact with the anisotropic stress of the cosmological fluid, mainly given by its neutrino component. While at the large scales this is effectively collisionless, in the small-scale limit, the collisions between neutrinos should be properly taken into account for the computation of the anisotropic stress. In this talk we will present the results of the integration of the Einstein-Boltzmann system of differential equations for the coupled gravitational wave-neutrino system, and we will discuss how this will affect the expected signal of stochastic gravitational waves.

Enhancement of the dark matter annihilation cross section in cold substructures

One of the possible explanations of the positron excess observed by the PAMELA experiment is that it is produced by the annihilation of TeV dark matter particles. However, if this interpretation is correct, the DM annihilation cross section has to be boosted with respect to the primordial value needed to obtain the correct dark matter abundance. A possible way to obtain the boost is via a low-energy enhancement of the cross section due to the presence of a potential between the annihilating particles (Sommerfeld effect). We will show that very large "boost factors" (of order ~ 10^3 or more) can be obtained in this way, and that the main contribution inside the galactic halo comes from the small, cold subhaloes, more than from the smooth halo component. We will discuss the expected diffuse gamma signal and the possibility of constraining the enhancement through the observation of dwarf galaxies like Draco and Sagittarius.

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