Type V singularities in non-standard cosmological backgrounds

TL;DR

This paper investigates the occurrence of Type V singularities, specifically w-singularities, across various non-standard cosmological models, revealing surprising similarities and differences with standard cosmology.

Contribution

It provides the first comprehensive analysis of w-singularities in multiple non-standard cosmologies, including braneworld, f(R) gravity, and quantum-inspired models.

Findings

w-singularities occur under similar conditions across different non-standard cosmologies with power series scale factors.

Exponential scale factors lead to similar singularity conditions in RS-II and Chern-Simons models as in standard cosmology.

f(R) gravity models exhibit distinct conditions for Type V singularities compared to other non-standard models.

Abstract

Interest in cosmological singularities has remarkably grown in recent times, particularly on future singularities with the discovery of late-time acceleration of the universe and dark energy. Recent work has seen a proper classification of such singularities into strong and weak based on their strength, with weak singularities being the likes of sudden, w and big freeze singularities and strong singularities like the big rip. While there has been an expansive literature which has discussed the occurrence of Type I-IV in many non-standard cosmologies, w-singularities have not yet been explored in exotic cosmological settings. So in this work we pursue the same and discuss the status quo of w-singularities in a variety of non-standard cosmologies. We consider the RS-II Braneworld cosmology, an F(R) gravity cosmology which gives viable late time acceleration. We also consider cosmologies due to modified area-entropy relations, generalized uncertainty principles, holographic renormalization and Chern-Simons gravity( all of which can be coincidentally described by the same form of the modified Friedmann equation). We show that w-singularities will occur in exactly the same conditions in all these vividly different cosmological settings as they do in the usual general relativistic cosmology if one considers a power series expansion ansatz for the scale factor. We also show that if one considers an exponential form of the scale factor then while Type V singularities in the RS-II Braneworld and Chern-Simons cosmologies occur in the same conditions as in the standard cosmology case, there is a significant difference in the conditions when one considers the f(R) gravity case. These results are surprising overall, as one would usually not expect cosmological singularities to occur in almost the same conditions in non-standard cosmologies as they do in the usual standard cosmology.