Axion dark matter from Higgs inflation with an intermediate H_*

Abstract

In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H * O(10 9 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H * ∼ 10 8 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m 0 0.05 µeV for a quartic Higgs self-coupling λ φ = 0.1, which correspond to the PQ breaking scale v σ 10 14 GeV and tensor-to-scalar ratio r ∼ 10 −12 . Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.

Tracing the high energy theory of gravity: an introduction to Palatini inflation

“…[93] for a recent review on metric Higgs inflation and Refs. [14,22,30,32,36,39,42,43,46,47,53] for recent studies on Palatini-Higgs inflation. The model is specified by…”

Non-minimal (self-)running inflation: metric vs. Palatini formulation

“…At the present date, all the comparative studies between the metric and Palatini formulations either consider only a classical tree-level analysis [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] or assume that the leading contribution to radiative corrections is coming from some other additional particle (inside the Standard Model [54][55][56] or beyond it [57][58][59][60]) rather than the inflaton itself. While there have been several works about self-induced radiative corrections for a nonminimal inflaton in the metric case (e.g.…”

“…In figure 1 we are presenting the results for the metric formulation and plotting r vs. n s (a), r vs. ξ (b), ξ vs. n s (c) and λ 0 vs. ξ (d) for λ eff = λ app (cyan), λ eff = λ I (blue, dashed) and λ eff = λ II (magenta, dot-dashed) with N e = 50 e-folds. For reference we also plot predictions of quartic (brown), quadratic (black) and linear (yellow) inflation for N e ∈ [50,60]. The gray areas represent the 1, 2σ allowed regions coming from Planck 2018 data [9].…”

Reheating in R2 Palatini inflationary models

“…These couplings are different in the two approaches. This has been first pointed out in [13] and has attracted the interest of many authors since, , with still continuing activity, [43][44][45][46][47][48][49].…”