http://arxiv.org/abs/1311.5297
The observed dark matter (DM) abundance can be created from a thermal bath after the interaction rate which keeps the DM particles in thermal equilibrium falls below the expansion rate of the Universe. DM can also be excited directly from the inflaton or moduli decay, along with the excitation of the Standard Model degrees of freedom. Here we discuss the evolution of the DM abundance from the very onset of its creation from the inflaton decay. Based on the initial conditions such as the inflaton mass and its decay branching ratio to the DM, the reheating temperature, and the mass and interaction rate of the DM with the thermal bath, the DM particles can either thermalize or remain non-thermal throughout their evolution history. In the thermal case, the final abundance can be set by the standard freeze-out mechanism for large annihilation rates, irrespective of the initial condition. For smaller annihilation rates, it can be set by the freeze-in mechanism, also independent of the initial abundance, provided it is small to begin with. For even smaller interaction rates, the DM becomes non-thermal, and the relic abundance will be essentially set by the initial condition. Also depending on its mass and interaction rate, the DM could remain relativistic, thus acting like a dark radiation, or could behave as a warm or cold relic. We put model-independent constraints on the DM mass and annihilation rate from over-abundance, and compare with complementary constraints derived from indirect search experiments, Big Bang Nucleosynthesis, Cosmic Microwave Background, Planck measurements, and theoretical constraints from the unitarity of the scattering matrix. For the non-thermal DM scenario, we also show the allowed parameter space in terms of the inflaton and DM masses for a given reheating temperature, and compute the comoving free-streaming length to identify the hot, warm and cold DM regimes.
Fri, 22 Nov 13
42/66
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