Inflation in scale-invariant theories of gravity

TL;DR

This paper explores scale-invariant gravity models with loop corrections that can produce a tensor-to-scalar ratio compatible with recent observational constraints, offering an alternative to traditional inflation models.

Contribution

It demonstrates that quadratic, renormalizable, and scale-invariant gravity models with loop corrections can generate observable inflationary predictions within current experimental bounds.

Findings

The model predicts a tensor-to-scalar ratio larger than Starobinsky's but within observational limits.

Loop corrections in scale-invariant gravity can produce viable inflationary scenarios.

The approach aligns with recent Planck and BICEP2 constraints.

Abstract

Thanks to the Planck Collaboration, we know the value of the scalar spectral index of primordial fluctuations with unprecedented precision. In addition, the joint analysis of the data from Planck, BICEP2, and KEK has further constrained the value of the tensor-to-scalar ratio $r$ so that chaotic inflationary scenarios seem to be disfavoured. Inspired by these results, we look for a model that yields a value of $r$ that is larger than the one predicted by the Starobinsky model but is still within the new constraints. We show that purely quadratic, renormalizable, and scale-invariant gravity, implemented by loop-corrections, satisfies these requirements.