BICEP/Keck data and Quadratic Gravity

TL;DR

This paper explores how quadratic gravity modifications can reconcile certain inflationary models, like Higgs and natural inflation, with BICEP/Keck observational constraints, by computing their predictions within this extended gravity framework.

Contribution

It demonstrates that quadratic gravity can restore compatibility of Higgs and natural inflation models with observational data, extending their viability beyond Einstein gravity.

Findings

Quadratic gravity aligns Higgs inflation with BICEP/Keck constraints.

Natural inflation becomes compatible with observations under quadratic gravity.

Quadratic terms can UV complete gravity while maintaining stability and unitarity.

Abstract

The recent results of the BICEP and Keck collaborations have put stringent bounds on many inflationary models, including some well-motivated ones. This is certainly the case when gravity remains described by Einstein's theory up to the inflationary scale, but can be avoided by introducing quadratic-in-curvature terms that are effective at that scale. Recently it has also been shown that these terms can UV complete gravity respecting stability and unitarity. Here the predictions of such quadratic gravity are computed and compared with the BICEP/Keck constraints by focusing on some of the inflationary scenarios that are best-motivated from the particle physics point of view and are already ruled out in Einstein gravity: (critical) Higgs inflation and natural inflation. The first scenario can be considered as the most economical option as the inflaton is identified with the only known elementary scalar field in the Standard Model and the near criticality of the Standard Model is used to remain in the perturbative regime. In the second one a pseudo-Nambu-Goldstone boson contributes to the inflationary dynamics and its potential is naturally flat. It is shown that in both scenarios one can restore the agreement with the observational constraints in quadratic gravity.