Abstract:
It is observed that the universe expanding with repulsive force. Dark en-
ergy is an unknown force and responsible for current cosmic acceleration.
Generally, in order to ¯nd the best-¯t model to discuss the cosmic accel-
eration and dark energy phenomenon, there are two directions that are
dynamical dark energy models and modi¯ed theories of gravity. One of
the dynamical model is holographic dark energy which is also modi¯ed
in di®erent forms such as modi¯ed, generalized, Tsallis, Renyi, Sharma-
Mittal holographic dark energy models, etc. The modi¯ed theories include
fractal cosmology, Dvali-Gabadadze-Porrati braneworld, second Randall-
Sundrum braneworld, loop quantum cosmology, dynamical Chern-Simons
gravity, f(R); f(T); f(R; T) theories of gravity etc. Taking some of these
models and theories, researchers established di®erent cosmological parame-
ters.
In this thesis, we use Tsallis holographic dark energy model with gen-
eralized ghost pilgrim dark energy as infra-red cuto® for modi¯ed theo-
ries of gravity such as cyclic universe, Dvali-Gabadadze-Porrati braneworld,
Randal-Sundrum II braneworld and dynamical Chern-Simons theory in the
°at Friedmann-Robertson-Walker universe. In these directions, we study
some cosmological parameters like equation of state, deceleration parame-
ter, squared sound speed and Om (combination of Hubble and cosmos red-
shift parameter) parameter. We also establish some cosmic planes such as
! ¡ !0 and r ¡ s on the basis of present day observational data.
