Abstract
High-precision observational data have confirmed with startling evidence that the Universe is currently undergoing a phase of accelerated expansion. This phase, one of the most important and challenging current problems in cosmology, represents a new imbalance in the governing gravitational equations. Historically, physics has addressed such imbalances by either identifying sources that were previously unaccounted for or by altering the gravitational theory. Several candidates, responsible for this expansion, have been proposed in the literature, in particular dark energy models and modified gravity models, amongst others. Outstanding questions are related to the nature of this so-called “dark energy” that is driving this acceleration, and whether it is due to the vacuum energy or a dynamical field. On the other hand, the late-time cosmic acceleration may be due to modifications of general relativity. In this work, we explore a generalised modified gravity theory, namely ƒ(R,Φ, X) gravity, where R is the Ricci scalar, R is a scalar field and X is a kinetic term. This theory contains a wide range of dark energy and modified gravity models. We considered specific models and applications to the late-time cosmic acceleration.
Highlights
A central theme in cosmology is the fact that the Universe is currently undergoing an accelerating expansion [1,2]
What is the so-called “dark energy” that is driving the cosmic acceleration? Is it a vacuum energy or a dynamical field? Is the acceleration due to modifications of Einstein’s theory of general relativity (GR)? How is structure formation affected in these alternative scenarios? What happens to the Universe in the asymptotic future?
Curvature-matter couplings have been extensively analysed [14,15,16,17,18,19,20]. While these modified theories of gravity offer an alternative explanation to the standard cosmological model for the expansion history of the Universe [21], it offers a paradigm for nature fundamentally distinct from dark energy models of cosmic acceleration [22], even those that perfectly mimic the same expansion history
Summary
A central theme in cosmology is the fact that the Universe is currently undergoing an accelerating expansion [1,2]. Curvature-matter couplings have been extensively analysed [14,15,16,17,18,19,20] While these modified theories of gravity offer an alternative explanation to the standard cosmological model for the expansion history of the Universe [21], it offers a paradigm for nature fundamentally distinct from dark energy models of cosmic acceleration [22], even those that perfectly mimic the same expansion history. It is fundamental to understand how one may differentiate these modified theories of gravity from dark energy models In this context, a promising way to explain the late-time cosmic acceleration is to assume that at large scales, Einstein’s theory of GR breaks down, and a more general action describes the gravitational field.
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