Browsing by Author "Singh, Parampreet"

Now showing 1 - 7 of 7

Avoidance of future singularities in loop quantum cosmology
(2006-05-21) Sami, M.; Singh, Parampreet; Tsujikawa, Shinji
We consider the fate of future singularities in the eﬀective dynamics of loop quantum cosmology. Non-perturbative quantum geometric eﬀects which lead to ρ2 modiﬁcation of the Friedmann equation at high energies result in generic resolution of singularities whenever energy density ρ diverges at future singularities of Friedmann dynamics. Such quantum eﬀects lead to the avoidance of a Big Rip, which is followed by a recollapsing universe stable against perturbations. Resolution of sudden singularity, the case when pressure diverges but energy density approaches a ﬁnite value depends on the ratio of the latter to a critical energy density of the order of Planck. If the value of this ratio is greater than unity, the universe escapes the sudden future singularity and becomes oscillatory.
Can brane cosmology with a vanishing /\ explain the observations?
(2011-07-05) Vishwakarma, R. G.; Singh, Parampreet
A plethora of models of the universe have been proposed in recent years claiming that the present universe is accelerating, being driven by some hypothetical source with negative pressure collectively known as dark energy which though do not appear to resemble any known form of matter tested in the laboratory. These models are motivated by the high redshift supernovae Ia observations. Though low density models, without dark energy, also appear to ﬁt the SN Ia data reasonably well, however, they are ruled out by the CMB observations. In this paper, we present a warped brane model with an additional surface term of brane curvature scalar in the action. This results in shifting the dynamical curvature of the model from its geometrical counterpart, which creates profound consequences. Even for Λ = 0, the low energy decelerating model successfully explains the observed locations of the peaks in the angular power spectrum of CMB. This model also ﬁts the high redshift supernovae Ia observations, taken together with the recently observed SN 1997ﬀ at z ≈ 1.7, very well. Additionally, it also ﬁts the data on the angular size and redshift of the compact radio sources very well.
Cosmological Dynamics of Phantom Field
(2011-07-05) Singh, Parampreet; Sami, M.; Dadhich, Naresh
We study the general features of the dynamics of the phantom ﬁeld in the cosmological context. In the case of inverse coshyperbolic potential, we demonstrate that the phantom ﬁeld can successfully drive the observed current accelerated expansion of the universe with the equation of state parameter wφ < −1. The de-Sitter universe turns out to be the late time attractor of the model. The main features of the dynamics are independent of the initial conditions and the parameters of the model. The model ﬁts the supernova data very well, allowing for −2.4 < wφ < −1 at 95 % conﬁdence level
Derivation of the Maxwell equations and the relation between electric and magnetic charge
(2015-03-01) Singh, Parampreet; Dadhich, Naresh
Field theories from the relativistic law of motion
(2001-06-02) Singh, Parampreet; Dadhich, Naresh
From the relativistic law of motion we attempt to deduce the ﬁeld theories corresponding to the force law being linear and quadratic in 4-velocity of the particle. The linear law leads to the vector gauge theory which could be the abelian Maxwell electrodynamics or the non-abelian Yang-Mills theory. On the other hand the quadratic law demands spacetime metric as its potential which is equivalent to de- manding the Principle of Equivalence. It leads to the tensor theory of gravitational ﬁeld - General Relativity. It is remarkable that a purely dynamical property of the force law leads uniquely to the correspond- ing ﬁeld theories
Gravitationally induced neutrino asymmetry
(2011-07-05) Singh, Parampreet; Mukhopadhyay, B.
We study the propagation of Dirac neutrinos in gravitational backgrounds and show that the gravitational interaction can lead to neutrino asymmetry due to modi cations in dispersion relation. We give some examples of spacetime geometries where such asym- metry can arise. This asymmetry would have contributed to the relic neutrino asymmetry through the interaction of neutrinos with primordial black holes before neutrinos decou- pled. In the present epoch it may be generated in accretion around high temperature rotating black holes.
Non-conformally flat bulk spacetime and the 3-brane world
(2001-01-05) Singh, Parampreet; Dadhich, Naresh
We show that for non-conformally ﬂat bulk spacetime, there exist no bound modes for zero mass graviton on the 3-brane. The brane world model is therefore unstable for the bulk spacetime being diﬀerent from the conformally ﬂat anti - de Sitter space.