Lorentzian Vacuum Transitions in $f(R)$ gravity

TL;DR

This paper investigates vacuum transition probabilities in $f(R)$ gravity, extending quantum cosmology methods to modified gravity, providing analytic solutions for specific models and analyzing the effects of curvature and Ricci scalar assumptions.

Contribution

It extends the analysis of vacuum transitions to $f(R)$ gravity, deriving analytic expressions for transition probabilities in various curvature scenarios and models.

Findings

Transition probabilities are similar to Einstein gravity with quantum corrections.

Constant Ricci scalar assumption simplifies calculations but is invalid in positive curvature cases.

Explicit solutions are obtained for power-law $f(R)$ models.

Abstract

We study Lorentzian vacuum transition probabilities between two minima of a scalar field potential within the framework of $f(R)$ gravity. The analysis extends the previously considered WKB expansion of the Wheeler-DeWitt equation to modified gravity theories, up to second order. We apply the general method for homogeneous and isotropic FLRW universes, with zero and positive spatial curvature, for any $f(R)$ model. For the flat case we obtain analytic expressions for the transition probabilities for any model if we assume a constant Ricci scalar; this assumption has been considered in previous studies, in the Euclidean approach, from symmetry arguments. On the other hand, we also obtain explicit solutions without this assumption for power-law $f(R)=R^{1+n}$ models. Moreover, in the positive curvature scenario, we obtain that the assumption of a constant Ricci scalar is not consistent, but we are able to find analytical solutions in approximated regimes. In all cases we have found that the general behavior of the probabilities already found for Einstein Gravity is preserved, including the prediction of a non-singular initial state due to quantum corrections, even though the probabilities increase or decrease in a model dependent way.