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Abstract:

During (re)heating of the universe after inflation, the relativistic decay products of the inflaton field $\phi$ must lose energy and additional particles must be produced to attain a thermalised state at a temperature $T_{\reh}$. We estimate the rate of energy loss via elastic and inelastic scattering interactions. Elastic scattering is an inefficient energy loss mechanism so inelastic processes, although higher order in the coupling $\alpha$, can be faster because more energy is transfered. The timescale to produce a particle number density of ${\cal O}(T_{\reh}^3)$ is the inelastic energy loss timescale, $\sim(\alpha^3 n_\phi/T_{\reh}^2)^{-1}$.

Abstract:

The possibility that the Fermi scale is the only fundamental energy scale of Nature is under serious consideration at present, yet cosmic rays may already have provided direct evidence of new physics at a much higher scale. The recent detection of very high energy particles with no plausible astrophysical sources suggests that these originate from the slow decays of massive particles clustered in the halo of our Galaxy. Such particles had in fact been predicted to exist beforehand with mass and lifetime in the range required to explain the observations. I discuss recent work focussing on experimental tests of this speculative but exciting idea.