Sudden singularities in generalized hybrid metric-Palatini cosmologies

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.

Finite-time cosmological singularities and the possible fate of the Universe

“…This pioneering work initiated the investigation of the possible occurrence of finitetime future singularities in the context of various DE models originating from various theoretical contexts. It was reported by a number of investigators that cosmological models may develop a variety of finite-time singularities in the future and the Big Rip singularity is not alone in the list of finite-time future singularities appearing in several cosmological models, there may appear other types of finite-time singularities in the cosmological models, such as the sudden singularity [350] (also see [351][352][353][354][355][356][357][358][359][360][361][362][363][364][365][366][367][368][369]), the big freeze singularity [370], the generalized sudden singularity [371], w singularity [372,373]. The appearance of such finite-time future cosmological singularities became an important part of modern cosmology and this got massive attention in the scientific community.…”

“…[374] and for an important stream of articles on finitetime cosmological singularities, see Refs. [361,363,367, and the references therein. Note that the possibility of finite time singularities in the context of inflation was investigated and some models along this line were proposed [447,448].…”

Weak-field regime of the generalized hybrid metric-Palatini gravity

“…This implies the existence of a long-range scalar field, which is able to modify the cosmological [26,27] and galactic dynamics [28,29], but leaves the Solar System unaffected [30]. A plethora of applications exist in the literature, such as in cosmology [31][32][33][34][35][36] and extra-dimensions [37,38], stringlike configurations [39,40], black holes and wormholes [41][42][43][44][45], stellar configurations [46], tests of binary pulsars [47], observational constraints [48], among other applications (we refer the reader to [23,24] for more details). However, one may consider further generalizations of the linear hybrid metric-Palatini theory, by taking into account an fðR; RÞ extension [49,50].…”