f (R,T) reconstruction models in FLRW cosmologies

Abstract

The concept of gravity is very important yet there is no complete description on how this force actually works. It can be a manifestation of curvature in the geometry of spacetime, as postulated by Einstein, or something else. Although the General Relativity viewpoint turned out to be the most successful theory in describing gravity, it is still an incomplete theory of gravity since it fails at explaining certain phenomena that are currently being observed such as galactic rotation curves and the accelerated expansion of the Universe in recent times. As a result cosmologists are trying to find alternative theories of gravity that are consistent with the current observations. In this thesis, we will investigate f ( R, T) modified theories of gravity and by assuming that the expansion history of the universe is known, we invert the field equations to get to determine which modified theory gives a fiat Friedmann-Robertson-\i\Talker model. In this thesis we are also going to modify j(T) (where T is the trace of the energy-momentum tensor) models of gravity to obtain a new solution for the scale factor, Hubble parameter and deceleration parameter in terms of the cosmic time. A completely new toy model, that describes the cosmic evolution from 13. 7 billion years ago till the present time, will be proposed which is found to be consistent with dark energy; something that the original theory of general relativity does not predict. This toy model is further extended to examine the scale factor behaviour in the nearby and distant future so that the fate of the universe can be determined.