A viable Starobinsky-like inflationary scenario in the light of Planck and BICEP2 results

TL;DR

This paper compares three Starobinsky-like inflation models against recent Planck and BICEP2 data, highlighting a class of running vacuum models that predict a tensor-to-scalar ratio compatible with observations.

Contribution

It introduces a class of decaying vacuum $ ext{Λ}(H)$ cosmologies that unify the universe's entire evolution and match recent CMB measurements.

Findings

The $ ext{Λ}(H)$ models predict $r \,\simeq\, 0.16$, consistent with BICEP2 results.

The models provide a complete cosmic history from inflation to late-time acceleration.

They offer a viable alternative to traditional inflationary scenarios.

Abstract

The recent CMB data from Planck and BICEP2 observations have opened a new window for inflationary cosmology. In this Essay we compare three Starobinsky-like inflationary scenarios: (i) the original Starobinsky proposal; (ii) a family of dynamically broken SUGRA models; and (iii) a class of "decaying" vacuum $\Lambda(H)$ cosmologies. We then focus on the $\Lambda(H)$ variant, which spans the complete cosmic history of the universe from an early inflationary stage, followed by the "graceful exit" into the standard radiation regime, the matter epoch and, finally, the late-time accelerated expansion. Computing the effective potential we find that the "running" $\Lambda(H)$ models also provide a prediction for the tensor-to-scalar ratio of the CMB spectrum, $r \simeq 0.16$, which is compatible to within $1\sigma$ with the value $r=0.20^{+0.07}_{-0.05}$ recently measured by the BICEP2 collaboration.