Unsuccessful cosmology with modified gravity models

Modified gravity and cosmology

Non-singular Cosmology in Modified Gravity

A non-singular cosmology is derived in modified gravity (MOG). The universe begins in the distant past in a contracting de Sitter phase, is non-singular at t = 0 and then describes approximately the standard radiation dominated solution before the time of decoupling. The spacetime in the neighborhood of t = 0 is described by Minkowski spacetime in which the Weyl curvature tensor vanishes and th...

Inflationary Cosmology in Modified Gravity Theories

We review inflationary cosmology in modified gravity such as R gravity with its extensions in order to generalize the Starobinsky inflation model. In particular, we explore inflation realized by three kinds of effects: modification of gravity, the quantum anomaly, and the R term in loop quantum cosmology. It is explicitly demonstrated that in these inflationary models, the spectral index of sca...

Cuscuton Cosmology: Dark Energy meets Modified Gravity

In a companion paper [1], we have introduced a model of scalar field dark energy, Cuscuton, which can be realized as the incompressible (or infinite speed of sound) limit of a k-essence fluid. In this paper, we study how Cuscuton modifies the constraint sector of Einstein gravity. In particular, we study Cuscuton cosmology and show that even though Cuscuton can have an arbitrary equation of sta...

Viscous Frw Cosmology in Modified Gravity

We discuss a modified form of gravity implying that the action contains a power α of the scalar curvature. Coupling with the cosmic fluid is assumed. As equation of state for the fluid, we take the simplest version where the pressure is proportional to the density. Based upon a natural ansatz for the time variation of the scale factor, we show that the equations of motion are satisfied for gene...