120697597
Static cosmic strings in Brans-Dicke theory
119358901
WMAP constraints on Cardassian model
We have investigated the constraints on the Cardassian model using the recent results from the Wilkinson Microwave Anisotropy Probe (WMAP) for the locations of the peaks of the Cosmic Microwave Background (CMB) anistropy spectrum. We find that the model is consistent with the recent observational data for certain range of the model parameter $n$ and the cosmological parameters. We find that the Cardassian model is favoured compared to $\Lambda$CDM model, for a higher spectral index ($n_s \approx 1$) together with lower value of Hubble parameter $h$ ($h\leq 0.71$). But for smaller values of $n_s$, both $\Lambda$CDM and Cardassian are equally favoured. Also, irrespective of Supernova constraint, CMB data alone predicts current acceleration of the universe in this model. We have also studied the constraint on the $\sigma_{8}$, the rms density fluctuations at $8h^{-1}$ Mpc scale.
118614329
Reconstructing the interaction rate in holographic models of dark energy
Abstract We reconstruct the interaction rate of the holographic dark energy model recently proposed by Zimdahl and Pavon [W. Zimdahl, D. Pavon, Class. Quantum Grav. 24 (2007) 5461] in the redshift interval 0 z 1.8 with observational data from supernovae type Ia, baryon acoustic oscillations, gas mass fraction in galaxy clusters, and the growth factor. It shows a reasonable behavior in the sense that it increases with expansion from a small or vanishing value in the long past but starts decreasing at recent times. The later feature suggests that the equation of state parameter of dark energy does not cross the phantom divide.
118586619
Cosmology with non-minimally coupled k-field
We consider a non-minimally coupled (with gravity) scalar field with non-canonical kinetic energy. The form of the kinetic term is of Dirac–Born–Infeld form. We study the early evolution of the universe when it is sourced only by the k-field, as well as late time evolution when both the matter and k-field are present. For the k-field, we have considered constant potential as well as potential inspired from boundary string field theory. We show that it is possible to have an inflationary solution in early time as well as late time accelerating phases. The solutions also exhibit attractor properties in a sense that they do not depend on the initial conditions for certain values of the parameters.
118981720
The weak energy condition and the expansion history of the Universe
We examine flat models containing a dark matter component and an arbitrary dark energy component, subject only to the constraint that the dark energy satisfies the weak energy condition. We determine the constraints that these conditions place on the evolution of the Hubble parameter with redshift, H(z), and on the scaling of the coordinate distance with redshift, r(z). Observational constraints on H(z) are used to derive an upper bound on the current matter density. We demonstrate how the weak energy condition constrains fitting functions for r(z).
120897327
VACUUMLESS COSMIC STRINGS IN BRANS–DICKE THEORY
The gravitational fields of vacuumless global and gauge strings have been studied in Brans–Dicke theory under the weak field assumption of the field equations. It has been shown that both global and gauge string can have repulsive as well as attractive gravitational effect in Brans–Dicke theory which is not so in General Relativity.
16109922
Non-BPS D-branes in string theory
In this paper I shall discuss some aspects of non-BPS D-branes in string theory. PACS number: 1125