Cosmology in time asymmetric extensions of general relativity

TL;DR

This paper explores how time asymmetric modifications to general relativity can lead to diverse cosmological behaviors, including accelerated expansion, matter domination, and cyclic universes, all consistent with observations.

Contribution

It introduces a novel class of modified gravity theories with time asymmetric terms that preserve local physics but significantly alter cosmological evolution.

Findings

Universe can be dark-energy dominated without a cosmological constant

Models exhibit quintessence-like, phantom-like, or effective cosmological constant behaviors

Possible cyclic or bouncing cosmologies in closed universe scenarios

Abstract

We investigate the cosmological behavior in a universe governed by time asymmetric extensions of general relativity, which is a novel modified gravity based on the addition of new, time-asymmetric, terms on the Hamiltonian framework, in a way that the algebra of constraints and local physics remain unchanged. Nevertheless, at cosmological scales these new terms can have significant effects that can alter the universe evolution, both at early and late times, and the freedom in the choice of the involved modification function makes the scenario able to produce a huge class of cosmological behaviors. For basic ansatzes of modification, we perform a detailed dynamical analysis, extracting the stable late-time solutions. Amongst others, we find that the universe can result in dark-energy dominated, accelerating solutions, even in the absence of an explicit cosmological constant, in which the dark energy can be quintessence-like, phantom-like, or behave as an effective cosmological constant. Moreover, it can result to matter-domination, or to a Big Rip, or experience the sequence from matter to dark energy domination. Additionally, in the case of closed curvature, the universe may experience a cosmological bounce or turnaround, or even cyclic behavior. Finally, these scenarios can easily satisfy the observational and phenomenological requirements. Hence, time asymmetric cosmology can be a good candidate for the description of the universe.