False vacuum energy dominated inflation with large $r$ and the importance of $\kappa_s$

TL;DR

This paper explores the feasibility of false vacuum energy dominated inflation with a large tensor-to-scalar ratio, emphasizing the role of higher-order spectral index runnings and providing updated observational constraints.

Contribution

It derives bounds on false vacuum energy domination in inflation and highlights the significance of higher-order spectral runnings, especially $eta_s$, in such scenarios.

Findings

Upper bound on $V_0$ domination in inflation

Importance of $eta_s$ for $V_0$ dominated inflation

Updated cosmological parameter constraints including $eta_s$

Abstract

We investigate to which extent and under which circumstances false vacuum energy ($V_0$) dominated slow-roll inflation is compatible with a large tensor-to-scalar ratio $r = O(0.1)$, as indicated by the recent BICEP2 measurement. With $V_0$ we refer to a constant contribution to the inflaton potential, present before a phase transition takes place and absent in the true vacuum of the theory, like e.g. in hybrid inflation. Based on model-independent considerations, we derive an upper bound on the possible amount of $V_0$ domination and highlight the importance of higher-order runnings of the scalar spectral index (beyond $\alpha_s$) in order to realise scenarios of $V_0$ dominated inflation. We study the conditions for $V_0$ domination explicitly with an inflaton potential reconstruction around the inflaton field value 50 e-folds before the end of inflation, taking into account the present observational data. To this end, we provide the up-to-date parameter constraints within $\Lambda$CDM + $r$ + $\alpha_s$ + $\kappa_s$ using the cosmological parameter estimation code Monte Python together with the Boltzmann code CLASS.