Singular cosmological evolution using canonical and phantom scalar fields

TL;DR

This paper explores how Type IV finite time singularities can be integrated into cosmological models using single or multiple scalar fields, offering new scenarios for inflation and late-time acceleration, including in $F(R)$ gravity.

Contribution

It introduces two-field scalar-tensor models that avoid instabilities during phantom-divide crossing and realize various cosmological singularities, expanding the landscape of viable cosmological scenarios.

Findings

Type IV singularities can occur during inflation or late-time acceleration.

Two scalar fields help avoid instabilities at phantom-divide crossing.

Multiple scenarios including inflation and Big Rip are achievable.

Abstract

We demonstrate that finite time singularities of Type IV can be consistently incorporated in the Universe's cosmological evolution, either appearing in the inflationary era, or in the late-time regime. While using only one scalar field instabilities can in principle occur at the time of the phantom-divide crossing, when two fields are involved we are able to avoid such instabilities. Additionally, the two-field scalar-tensor theories prove to be able to offer a plethora of possible viable cosmological scenarios, at which various types of cosmological singularities can be realized. Amongst others, it is possible to describe inflation with the appearance of a Type IV singularity, and phantom late-time acceleration which ends in a Big Rip. Finally, for completeness, we also present the Type IV realization in the context of suitably reconstructed $F(R)$ gravity.