Lambodar P. Singh

COSMIC EVOLUTION IN GENERALISED BRANS–DICKE THEORY

We have studied the generalised Brans–Dicke theory and obtained exact solutions of a(t), ϕ(t) and ω(t) for different epochs of the cosmic evolution. We discuss how inflation, deceleration, cosmic acceleration can result from this solution. The time variation of G(t) is also examined.

TIME DEPENDENCE OF BRANS–DICKE PARAMETER ω FOR AN EXPANDING UNIVERSE

We have studied the time dependence of ω for an expanding universe in the generalised B-D theory and have obtained its explicit dependence on the nature of matter contained in the universe in different era. Lastly, we discuss how the observed accelerated expansion of the present universe can be accommodated in the formalism.We have studied the time dependence of w for an expanding universe in the generalised B-D theory and have obtained its explicit dependence on the nature of matter contained in the universe,in different era.Lastly we discuss how the observed accelerated expansion of the present universe can be accomodated in the formalism.

PRESENT ACCELERATION OF THE UNIVERSE, HOLOGRAPHIC ENERGY AND BRANS–DICKE THEORY

The present day accelerated expansion of the universe is naturally addressed within the Brans-Dicke theory just by using holographic dark energy model with inverse of Hubble scale as IR cutoff. It is also concluded that if the universe continues to expand, then one day it might be completely filled with dark energy.

Evolution of primordial black holes in Jordan–Brans–Dicke cosmology

We consider the evolution of primordial black holes in a generalized Jordan-BransDicke cosmological model where both the Brans-Dicke scalar field and its coupling to gravity are dynamical functions determined from the evolution equations. The evaporation rate for the black holes is different from the case in standard cosmology. We show that the accretion of radiation can proceed effectively in the radiation dominated era. It follows that the black hole lifetime shortens for low initial mass, but increases considerably for larger initial mass, thus providing a mechanism for the survival of primordial black holes as candidates of dark matter. We derive a cut-off value for the initial black hole mass, below which primordial black holes evaporate out in the radiation dominated era, and above which they survive beyond the present era.

GRAVITATIONAL WAVES IN GENERALISED BRANS–DICKE THEORY

We have solved cosmological gravitational Wave(GW)equation in the frame work of Generalised Brans-Dicke(GBD) theory for all epochs of the Universe.The solutions are expressed in terms of the present value of the Brans-Dicke coupling parameter

Astrophysical constraints on primordial black holes in Brans-Dicke theory

\omega(\phi)

Accretion, primordial black holes and standard cosmology

.It is seen that the solutions represent travelling growing modes for negative values of

DIRAC EQUATION IN SPATIALLY NONFLAT ROBERTSON-WALKER SPACE-TIMES: II

\omega_{0}

Evolution of Primordial Black Holes in Loop Quantum Cosmology

for all epochs of the Universe.

Phantom energy accretion and primordial black holes evolution in Brans-Dicke theory

We consider cosmological evolution in Brans-Dicke theory with a population of primordial black holes. Hawking radiation from the primordial black holes impacts various astrophysical processes during the evolution of the Universe. The accretion of radiation by the black holes in the radiation dominated era may be effective in imparting them a longer lifetime. We present a detailed study of how this affects various standard astrophysical constraints coming from the evaporation of primordial black holes. We analyze constraints arising from the present density of the Universe, the present photon spectrum, the distortion of the cosmic microwave background spectrum and also from processes affecting light element abundances after nucleosynthesis. We find that the constraints on the initial primordial black hole mass fractions are tightened with increased accretion efficiency.