Constraining non-thermal dark matter by CMB

Abstract

A period of early matter domination can give rise to the correct dark matter abundance for a broad range of dark matter annihilation rate ⟨ σann v ⟩f. Here, we examine this scenario for situations where ⟨ σann v ⟩f is below the nominal value for thermal dark matter 3 × 10−26 cm3 s−1 as possibly indicated by some recent experiments. We show that obtaining the correct relic abundance sets a lower bound on the duration of early matter domination era in this case. On the other hand, provided that the post-inflationary universe has an equation of state characterized by w ⩽ 1/3, the requirement that the scalar spectral index ns be within the observationally allowed range limits the duration of this epoch from above. By combining these considerations, we show that the current and future cosmic microwave background experiments can tightly constrain the parameter space for this scenario. In particular, models of inflation with a scalar-to-tensor ratio below \U0001d4aa(0.01) may disfavor non-thermal supersymmetric dark matter from a modulus-driven early matter domination epoch.