Higgs-Dilaton cosmology: Universality vs. criticality

TL;DR

The Higgs-Dilaton model explains both early inflation and late dark energy acceleration, with predictions sensitive to parameters, especially near critical points where observable values can significantly deviate from standard predictions.

Contribution

This work analyzes the Higgs-Dilaton model's predictions near criticality, revealing potential for large tensor-to-scalar ratios and deviations in dark energy behavior.

Findings

Predicted tensor-to-scalar ratio varies with model parameters.

Near criticality, the model allows for larger r and positive scalar tilt running.

Dark energy equation of state can significantly differ from a cosmological constant.

Abstract

The Higgs-Dilaton model is able to produce an early inflationary expansion followed by a dark energy dominated era responsible for the late time acceleration of the Universe. At tree level, the model predicts a small tensor-to-scalar ratio ($0.0021\leq r \leq 0.0034$), a tiny negative running of the spectral tilt ($-0.00057 \leq dn_s/d\ln k \leq -0.00034$) and a nontrivial consistency relation between the spectral tilt of scalar perturbations and the dark energy equation of state, which turns out to be close to a cosmological constant ($0 \leq 1+w_{DE} \leq 0.014$). We reconsider the validity of these predictions in the vicinity of the critical value of the Higgs self-coupling giving rise to an inflection point in the inflationary potential. The value of the inflationary observables in this case strongly depends on the parameters of the model. The tensor-to-scalar ratio can be large [$r\sim {\cal O}(0.1)$] and notably exceed its tree-level value. If that happens, the running of the scalar tilt becomes positive and rather big [$dn_s/d\ln k \sim {\cal O}(0.01)$] and the equation-of-state parameter of dark energy can significantly differ from a cosmological constant [$1+w_{DE}\sim {\cal O}(0.1)$].