Bounce universe with finite-time singularity

TL;DR

This paper investigates how a mild Type-IV singularity influences bouncing universe models within ghost-free Gauss-Bonnet gravity, finding that local effects of the singularity can produce observable predictions consistent with Planck data.

Contribution

It introduces a novel bouncing cosmology scenario where a Type-IV singularity has local effects, leading to viable models compatible with observational data.

Findings

Global effects of Type-IV singularity lead to incompatible perturbation spectra.

Local effects of the singularity produce perturbation modes consistent with observations.

Different timings of the singularity significantly alter the cosmological predictions.

Abstract

This work explains how the presence of a Type-IV singularity (a mild singularity) can influence the dynamics of a bouncing universe. In particular, we examine bounce cosmology that appears with a Type-IV singularity in the context of a ghost free Gauss-Bonnet theory of gravity. Depending on the time of occurrence of the Type-IV singularity, three different cases may arise -- when the singularity occurs before the bounce or after the bounce or at the instant of the bounce respectively. However in all of these cases, we find that in the case when the singularity "globally" affects the spacetime, the scalar power spectrum becomes red tilted and the tensor-to-scalar ratio is too large to be consistent with the observational data. Based on these findings, we investigate a different bouncing scenario which also appears with a Type-IV singularity, and the singularity affects the spacetime "locally" around the time when it occurs. As a result, and unlike to the previous scenario, the perturbation modes in the second bouncing scenario are likely to generate far away from the bounce in the deep contracting phase. This finally results to the simultaneous compatibility of the observable quantities with the Planck data, and ensures the viability of the bounce model where the Type-IV singularity has local effects on the spacetime around the time of the singularity.