Modified gravity. Problems and observational manifestations

TL;DR

This paper explores models of modified gravity, analyzing their evolution, singularities, and observational signatures, including implications for dark matter creation and universe dynamics during radiation domination.

Contribution

It introduces an analysis of $R^2$-extended gravity, examining singularity formation, particle production, and potential dark matter creation mechanisms.

Findings

Gravitating systems tend to evolve toward infinite curvature singularities.

Particle production by oscillating curvature is quantified.

Implications for non-thermal dark matter generation are discussed.

Abstract

Some models of modified gravity and their observational manifestations are considered. It is shown, that gravitating systems with mass density rising with time evolve to a singular state with infinite curvature scalar. The universe evolution during the radiation dominated epoch is studied in $R^2$-extended gravity theory. Particle production rate by the oscillating curvature is calculated. Possible implications of the model for cosmological creation of non-thermal dark matter are discussed.