Description |
We use the S-matrix unitarity to put constraints on the upper mass of a thermal dark matter whose annihilations proceed via generic k to 2 processes. These annihilations may be either within the standard model sector or dark sector. The bounds are first evaluated assuming radiation dominated universe during the freeze-out. We then extend the analysis to freeze-out during matter-dominated universe before the BBN era. Due to entropy dilution, the upper bound on the mass relaxes. We also find that reheating temperatures higher that O(200 GeV) for k=4, O(1 TeV) for k=3 and O(50 TeV) for k=2 are strongly disfavoured by the combined requirements of unitarity and dark matter relic abundance.
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