## SEARCH

#### Author

##### ( see all 229)

- Pradhan, Anirudh 5 (%)
- Dubrovich, V. K. 4 (%)
- Grachev, S. I. 4 (%)
- Padmanabhan, T. 4 (%)
- Seshadri, T. R. 4 (%)

#### Publication

##### ( see all 8)

- Pramana 31 (%)
- Astrophysics and Space Science 29 (%)
- Astronomy Letters 15 (%)
- Journal of Astrophysics and Astronomy 15 (%)
- Astrophysics 8 (%)

#### Subject

##### ( see all 8)

- Astronomy [x] 102 (%)
- Physics [x] 102 (%)
- Astrophysics 69 (%)
- Physics, general 32 (%)
- Astronomy, Astrophysics and Cosmology 5 (%)

## CURRENTLY DISPLAYING:

Most articles

Fewest articles

Showing 1 to 10 of 102 matching Articles
Results per page:

## Modelling the merging history of Binary SMBHs in Hierarchical Models of Galaxy Formation

### Astrophysics and Space Science (2002-07-01) 281: 501-504 , July 01, 2002

We present a model describing the evolution of a Super Massive Black Holes (SMBHs) population within the framework of hierarchical models of galaxy formation. The occurrence of SMBHs binaries at different redshifts and the influence of the interacting SMBHS on the host galaxies are studied by means of Montecarlo realizations of halo merging histories, coupled with a semi-analytical treatment of the interactions between the systems. We find that the main parameters governing the coalescence timescale, and hence the fraction of binary systems, are the initial mass and the accretion history of the SMBHs.

## The dimensional reduction of eleven dimensional supergravity into a product of Robertson-Walker spacetime and the seven sphere

### Pramana (1991-03-01) 36: 245-252 , March 01, 1991

The dimensional reduction of eleven dimensional supergravity is discussed. It is shown that there is no dimensional reduction onto Robertson-Walker space with the asymmetric tensor*F* giving a realistic fluid. Furthermore it is shown that the ansatz’s for the scale factor*R:R=at*^{n}, R=a exp (*bt*^{n}), and*R=aZ*^{n}, there is no dimensional reduction except the known example of the Freund-Rubin-Englert solution.

## Role of a scalar field in the radiation dominated epoch of the development of the universe

### Astrophysics (2008-01-01) 51: 121-129 , January 01, 2008

The recently discovered accelerated expansion of the universe is of current interest in theoretical research on the evolution of the universe. The cause of this behavior is presumably the presence of dark energy, which has been estimated to form up to 70% of the universe and generates a “repulsive force.” In this paper a cosmological model is constructed which takes the dark energy into account in a Jordan-Brans-Dicke tensor-scalar model with a dominant, nonminimally coupled scalar field in the presence of a cosmological scalar. The radiation dominant epoch is discussed.

## Black hole physics in globally hyperbolic space-times

### Pramana (1982-05-01) 18: 385-396 , May 01, 1982

The usual definition of a black hole is modified to make it applicable in a globally hyperbolic space-time. It is shown that in a closed globally hyperbolic universe the surface area of a black hole must eventually decrease. The implications of this breakdown of the black hole area theorem are discussed in the context of thermodynamics and cosmology. A modified definition of surface gravity is also given for non-stationary universes. The limitations of these concepts are illustrated by the explicit example of the Kerr-Vaidya metric.

## The Evolution of the Galaxy Luminosity Function: Theoretical Predictions vs. Observations

### Astrophysics and Space Science (2002-07-01) 281: 509-513 , July 01, 2002

We show that the canonical prescriptions adopted by current semi-analytic models (SAMs) of hierarchical galaxy formation lead to luminosity functions (LFs) too steep when compared with existing data (obtained from deep multicolor surveys in the HDF-N, HDF-S, NTT-DF in rest-frame B and UV (1700 Å) bands) at redshifts *z* > 1; the discrepancy grows to a factor ∼ 8 at *z* ≈ 3. Such result is robust with respect to different recipes for the feedback if this is assumed to arise from the effect of Supernovae contained in the galaxies. When the depletion of satellite galaxies in common haloes due to binary aggregations is taken into account, the discrepancy of SAM predictions with the observed LFs at *z* > 1 and at *z* ∼ 3 is appreciably reduced. At *z* ≈ 0 the effect of binary aggregations is to yield a flatter LF for -20 < *M*_{B} < -18, but with an upturn at the very faint end for M_{B}−16.

## Non-singular cosmologies in the conformally invariant gravitation theory

### Pramana (1976-11-01) 7: 344-354 , November 01, 1976

It is shown that in the framework of a conformally invariant gravitation theory, the singularity which is present in some anisotropic universes in general relativity is due to a wrong choice of conformal frame. Frames exist in which these models can be made singularity free.

## Angular fluctuations in the cosmic microwave background owing to initial perturbations in the radiation temperature

### Astrophysics (2007-10-01) 50: 515-524 , October 01, 2007

A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian perturbations of the CMBR.

## Gravitational fields with space-times of Bianchi type IX

### Pramana (1986-07-01) 27: 63-72 , July 01, 1986

Spatially homogeneous space-times of Bianchi type IX are considered. A general scheme for the derivation of exact solutions of Einstein’s equations corresponding to perfect fluid plus pure radiation fields is outlined. Some simple rotating Bianchi type IX cosmological models are presented. The details of these solutions are also discussed.

## Causal dissipation in Robertson-Walker cosmological models

### Pramana (1998-02-01) 50: 105-108 , February 01, 1998

Some of the Robertson-Walker cosmological models filled with a fluid with bulk viscosity have been derived which are consistent with causal thermodynamics. The models are discussed briefly.

## Statistical isotropy of the cosmic microwave background

### Pramana (2004-03-01) 62: 793-796 , March 01, 2004

The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra-large scale structure of the cosmos, in particular, of non-trivial cosmic topology. The statistical isotropy (SI) of the cosmic microwave background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond the cosmic horizon. We propose a set of measures,*K*_{l} (*l* = 1, 2,3,...) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically compute the predicted*K*_{l} spectra for CMB anisotropy in flat torus universe models. Characteristic signatures of different models in the*K*_{l} spectrum are noted.