The Higgs Portal to Cosmology

Abstract

The discovery of the Higgs boson has opened a new avenue for exploring physics beyond the Standard Model. In this review, we discuss cosmological aspects of the simplest Higgs couplings to the hidden sector, known as the Higgs portal. We focus on implications of such couplings for inflation, vacuum stability and dark matter, with the latter including both the traditional weakly interacting massive particles as well as feebly interacting scalars. The cosmological impact of the Higgs portal can be important even for tiny values of the couplings.

Exotic Higgs Decays

“…It is worth observing that while the "WIMP miracle" ensures that DM freezing out via (extended) Higgs portal interactions has a mass scale not too dissimilar from the electroweak scale, a priori there is no compelling theoretical reason to prefer DM masses either above or below m h /2. Detailed discussion of Higgs portal DM across the full viable mass range can be found in the recent reviews [39,40].…”

Challenges for Inflaton Dark Matter

“…In what follows, we take ξ φ , ξ h ≥ 0 to avoid a singularity at large field values. Cosmological implications of the Higgs portal models of this type have been reviewed in [28].…”

“…The Higgs pairs are generated by an oscillating classical background [43], [44], and the corresponding inflaton decay rate for 4 massless Higgs d.o.f. is given by [28]…”

“…In reality, the Higgs production is much more suppressed since the Higgs is heavy: the effective Higgs mass is much greater than the principal oscillation frequency of the inflaton, m eff h = λ φh /2 φ ω ∼ λ φ φ. This leads to exponential suppression of the decay rate by e −2π m eff h /ω [28]. Thus, perturbative decay can be neglected.…”

“…This bound applies at the TeV scale, while the couplings at the inflation scale are obtained by the solving the renormalization group (RG) equations. The list of the RG equations can be found in [28], while the most important one for us reads…”