About the isocurvature tension between axion and high scale inflationary models

TL;DR

This paper proposes a double field inflation model involving Peccei-Quinn Higgs to suppress axion isocurvature fluctuations at high inflation scales, potentially resolving the tension between axion models and high-scale inflation.

Contribution

It introduces a novel inflationary framework with explicit PQ symmetry violation terms, allowing a large axion decay constant and mitigating isocurvature issues at high inflation scales.

Findings

Suppression of axion isocurvature fluctuations at high inflation scales.

Large axion decay constant $f_a \\sim M_p$ achieved in the model.

Topological defect formation is analyzed and found not to be cosmologically problematic.

Abstract

The present work suggests that the isocurvature tension between axion and high energy inflationary scenarios may be avoided by considering a double field inflationary model involving the hidden Peccei-Quinn Higgs and the Standard Model one. Some terms in the lagrangian we propose explicitly violate the Peccei-Quinn symmetry but, at the present era, their effect is completely negligible. The resulting mechanism allows a large value for the axion constant, of the order $f_a\sim M_p$, thus the axion isocurvature fluctuations are suppressed even when the scale of inflation $H_{inf}$ is very high, of the order of $H_{inf}\sim M_{gut}$. This numerical value is typical in Higgs inflationary models. An analysis about topological defect formation in this scenario is also performed, and it is suggested that, under certain assumptions, their effect is not catastrophic from the cosmological point of view.