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## BD-FRW models in the framework of Israel-Stewart-Hiscock theory

### Pramana (1995-12-01) 45: 511-517 , December 01, 1995

BD-FRW universe filled with imperfect fluid having bulk viscosity is investigated under the framework of Israel-Stewart-Hiscock causal theory. The field equations have been solved by using the relation*φ*=*KR*^{α} where*K* and*α* are constants, between the Brans-Dicke scalar field*ϕ* and the scale factor*R*. This relation, in fact, leads to a constant deceleration parameter*q*. It is shown that the constancy of the deceleration parameter permits only two possibilities i.e. either*H*=constant with*m*=1 or*m*=(1+*b* −*α*)/(2(1+*b*) −*α*), irrespective of the value of*ɛ*.

## The quasi-steady state cosmology: Some recent developments

### Journal of Astrophysics and Astronomy (1997-12-01) 18: 353-362 , December 01, 1997

This paper summarises the recent work on the quasi-steady state cosmology. This includes, the theoretical formulation and simple exact solutions of the basic equations, their relationship to observations, the stability of solutions and the toy model for understanding the growth of structures in the universe.

## Cosmological models in general relativity

### Pramana (2003-12-01) 61: 1055-1063 , December 01, 2003

LRS Bianchi type-I space-time filled with perfect fluid is considered here with deceleration parameter as variable. The metric potentials*A* and*B* are functions of x as well as t. Assuming B′/B = f (x), where prime denotes differentiation with respect to x, it was found that*A = (l′/l)B* and*B = lS(t)*, where*l = f (x)* and*S* is the scale factor which is a function of t only. The value of Hubble’s constant*H*_{0} was found to be less than half for non-flat model and is equal to 1.3 for a flat model

## Higher dimensional spherically symmetric inhomogeneous cosmological model with heat flow

### Pramana (1995-06-01) 44: 495-500 , June 01, 1995

We study spherically symmetric inhomogeneous cosmological model with heat flow in higher dimensional space-time and present a class of solutions in which the velocity field is shear-free. Some of these solutions are analogous to the known solutions in 4-dimension while some are totally new.

## The Hubble relation for a comprehensive sample of QSOs

### Journal of Astrophysics and Astronomy (2003-03-01) 24: 11-21 , March 01, 2003

A correlation between redshifts (*z*) and apparent magnitudes (*V*) (Hubble relation) of Quasi Stellar Objects (QSOs) has long been sought. Such a correlation exists for galaxies whose redshifts are of cosmological origin. However, a plot of the two quantities representing the Hubble diagram for QSOs exhibits, in general, a wild scatter. This raises the question whether redshifts of QSOs are cosmological. On the other hand, most luminous QSOs in groups, and subsamples with particular properties, have been reported to show the Hubble relation. In the present paper, we analyse all optically non-variable QSOs in a comprehensive sample. In our analysis we grouped the objects into certain intervals of apparent magnitudes. Correlations obtained between redshifts and magnitudes are all statistically robust. Also, the Hubble relation in the usual form*V* = 5 log*z* +*C* is obeyed very convincingly for QSOs with*V* < 19.5.

## The inflationary Universe — From theory to observations

### Pramana (1998-07-01) 51: 27-37 , July 01, 1998

The inflationary Universe resolves some of the most outstanding issues of standard cosmology including the horizon and flatness problems and the origin of density fluctuations in the Universe. Inflationary models also predict the existence of a relic gravity wave background. Both gravity waves and density fluctuations induce fluctuations in the cosmic microwave background (CMB), the discovery of large angle anisotropies in the CMB having the scale invariant spectrum predicted by inflationary models has fuelled the hope that the inflationary scenario may indeed provide the correct description of the very early Universe. Upcoming large scale galaxy surveys (SDSS & 2dF) and CMB missions (MAP, Planck Surveyor) will further probe the inflationary scenario by throwing light on the origin and evolution of large scale structure in the Universe.

## Polarization of the cosmic microwave background radiation

### Pramana (1999-12-01) 53: 963-969 , December 01, 1999

In re-ionized models, the measurement of polarization of CMBR can be a good criterion to narrow down the parameter space for cosmological models. A Vishniac-type effect in second order polarization over arc minute scales has been calculated. It has been shown that while the effect is very small (∼10^{−2}*µ*K) for CDM models, it can be significant (∼0.3*µ*K) for some isocurvature models.

## Pancakes and filaments in cosmological gravitational clustering

### Pramana (1999-12-01) 53: 995-1000 , December 01, 1999

We consider the geometrical properties of a distribution of matter evolving under gravitational clustering. Such a distribution can be studied using standard statistical indicators such as the correlation function as well as geometrical descriptors sensitive to ‘connectedness’ such as percolation analysis and Minkowski functionals. Applying these methods to *N*-body simulations and galaxy catalogues we find that the filling factor at the percolation threshold is usually very small reflecting the fact that the Universe consists of a network of filaments and pancakes, the latter being statistically more prominent.

## Cosmology with cluster surveys

### Pramana (2004-10-01) 63: 871-875 , October 01, 2004

Surveys of clusters of galaxies provide us with a powerful probe of the density and nature of the dark energy. The red-shift distribution of detected clusters is highly sensitive to the dark energy equation of state parameter*w*. Upcoming Sunyaev-Zel’dovich (SZ) surveys would provide us large yields of clusters to very high red-shifts. Self-calibration of cluster scaling relations, possible for such a huge sample, would be able to constrain systematic biases on mass estimators. Combining cluster red-shift abundance with limited mass follow-up and cluster mass power spectrum can then give constraints on*w*, as well as on*σ*_{8} and Ω_{M} to a few per cents.

## Mini-bangs in cosmology and astrophysics

### Pramana (1974-03-01) 2: 158-170 , March 01, 1974

The ideas originally proposed to discuss continuous creation of matter are reconsidered in the context of the big bang cosmological models. It is shown that singularity-free big bang models are possible under the modified field equations of general relativity. However, the case is made out that matter creation takes place in several mini-bangs at different epochs rather than in one big bang. The implications of this idea for high energy astrophysics and for gravitational radiation are discussed.