Are There Closed Timelike Curves in $f(R,\mathcal{L}_m,\Phi,g^{\mu\nu}\nabla_\mu \Phi \nabla_\nu \Phi)$-Gravity?

TL;DR

This paper investigates the causal structure of specific rotating cosmological solutions within a generalized modified gravity model, finding these solutions inconsistent with the theory despite being solutions in general relativity.

Contribution

It analyzes the causal properties of rotating solutions in a broad class of modified gravity theories, revealing inconsistencies with these solutions.

Findings

Rotating cosmological solutions are exact in general relativity with matter.

Such solutions are inconsistent within the studied modified gravity model.

The analysis uses cylindrically symmetric and axially symmetric background geometries.

Abstract

A modified gravitational model whose action is given by an arbitrary function of the Ricci scalar, the matter Lagrangian density, a scalar field, and its kinetic term is investigated as an extension of the gravitational sector including an additional dynamical degree of freedom. Within this framework, the causal structure of rotating cosmological solutions is analyzed by considering a cylindrically symmetric Pertov-type N space-times and an axially symmetric Petrov type-III with a cosmological constant as background geometries used as theoretical probes of the model consistency. In both cases, pure radiation as matter sources are examined, including a scalar-field configurations. We demonstrate that, although the considered space-times are exact solutions to the field equations of general relativity with a matter source, they are inconsistent within the modified gravity theory considered here.