Abstract:
This thesis is devoted to explore stellar structures as well as evolution, gravitational
waves and viscous cosmology in the framework of modi¯ed theories of gravity. Firstly,
we study physical characteristics of stellar structures in the absence as well as presence
of electromagnetic ¯eld in the framework of f(R; T) theory. We consider the compact
stars whose pressure and density are related through polytropic equation of state
and MIT bag model. The energy conditions are satis¯ed and stellar con¯gurations
are found stable for the assumed values of free parameters. Secondly, we discuss
anisotropic non-static charged spherical as well as cylindrical sources describing the
phenomena of collapse and expansion in f(R; T) theory. We analyze the behavior of
density, pressures, anisotropic parameter as well as mass and examine the in°uence
of charge as well as model parameter on these quantities.
Thirdly, we ¯nd the polarization modes of gravitational waves for some f(R)
dark energy models with the help of Newman-Penrose formalism and ¯nd two extra
modes than general relativity. We also investigate the propagation of axial gravita-
tional waves in the background of °at FRW universe in f(R; T) theory through axial
perturbations. It is found that axial waves can induce velocity memory e®ect.
Finally, we consider viscous modi¯ed Chaplygin gas interacting with f(R; T) grav-
ity in °at FRW universe. We investigate the behavior of total energy density, pressure
and equation of state parameter for emergent, intermediate as well as logamediate
scenarios of the universe with two interacting models. It is found that bulk viscos-
ity enhances the expansion for the intermediate and logamediate scenarios. We also
study the evolution using LRS Bianchi type-I model and discuss the behavior of scale
factors as well as deceleration parameter in dark energy dominated era for di®erent
bulk viscosity models. We conclude that expansion is faster when bulk viscosity is
proportional to the Hubble parameter.
