Sudden singularities in generalized hybrid metric-Palatini cosmologies

TL;DR

This paper investigates the occurrence of sudden singularities in generalized hybrid metric-Palatini gravity, showing they can appear in higher derivatives of the scale factor and constraining their possible timing in the universe's evolution.

Contribution

It provides explicit solutions demonstrating sudden singularities in higher derivatives within this gravity model and compares these with observational data to constrain their occurrence.

Findings

Sudden singularities can occur in higher derivatives of the scale factor.

Explicit solutions show singularities appearing in the fourth derivative.

Observational constraints limit the possible timing of these singularities.

Abstract

In this work, we explore cosmological sudden singularities arising in the dynamically equivalent scalar-tensor representation of generalized hybrid metric-Palatini gravity. Using a FLRW background, we show that the structure of the field equations prevents sudden singularities from arising at time derivatives of the scale factor of orders lower than four, but that they are allowed to appear for time derivatives of higher orders. Imposing an ansatz for the scale factor, we provide an explicit solution where these sudden singularities appear in the fourth-order time derivative of the scale factor. A comparison of the Hubble and deceleration parameters arising from this model with the experimental measurements from the Planck Satellite allow us to impose constraints on the time span for which the occurrence of sudden singularities becomes likely in our universe, as measured from the Big Bang.