Standard model Higgs field and hidden sector cosmology

Understand

We consider scenarios where the inflaton field decays dominantly to a hidden dark matter (DM) sector.

• By studying the typical behavior of the Standard Model (SM) Higgs field during inflation, we derive a relation between the primordial tensor-to-scalar ratio $r$ and amplitude of the residual DM isocurvature perturbations $\beta$ which is typically generated if the DM is thermally decoupled from the SM sector.
• We consider different expansion histories and find that if the Universe was radiation- or matter-dominated after inflation, a future discovery of primordial DM isocurvature will rule out all simple scenarios of this type because generating observable $\beta$ from the Higgs is not possible without violating the bounds on $r$.
• Seen another way, the Higgs field is generically not a threat to models where both the inflaton and DM reside in a decoupled sector.