Reconciling inflation with openness

TL;DR

This paper demonstrates that an open universe with low density parameter can be naturally explained within inflationary models through bubble nucleation, aligning observational data with theoretical predictions.

Contribution

It shows that the probability of living in a bubble with the observed density parameter is high, reconciling open universe observations with inflationary theory using modified gravity models.

Findings

Probability of living in a suitable bubble is high

Open universe with low density parameter compatible with inflation

Supports primordial phase transition in inflationary models

Abstract

It is already understood that the increasing observational evidence for an open Universe can be reconciled with inflation if our horizon is contained inside one single huge bubble nucleated during the inflationary phase transition. In this frame of ideas, we show here that the probability of living in a bubble with the right $\Omega_0$ (now the observations require $\Omega_0 \approx .2$) can be comparable with unity, rather than infinitesimally small. For this purpose we modify both quantitatively and qualitatively an intuitive toy model based upon fourth order gravity. As this scheme can be implemented in canonical General Relativity as well (although then the inflation driving potential must be designed entirely ad hoc), inferring from the observations that $\Omega_0 < 1$ not only does not conflict with the inflationary paradigm, but rather supports therein the occurrence of a primordial phase transition.