136,141 research outputs found
Emergent Schwarzschild and Reissner-Nordstrom black holes in 4D: An effective curvature sourced by a B2-field on a D4-brane
We obtain a Schwarzschild and a Reissner-Nordstrom emergent black holes, by
exploring the torsion dynamics in a generalized curvature formulation,
underlying an effective D4-brane on S1. It is shown that a constant effective
metric, sourced by a background fluctuation in B2-potential, on a D3-brane
receives a dynamical quantum correction in presence of an electric charge.Comment: 7-pages, minor corrections, references added, to appear in Physical
Review
Quintessence and effective AdS brane geometries
A geometric torsion dynamics leading to an effective curvature in a second
order formalism on a D4-brane is revisited with a renewed interest. We obtain
two effective brane geometries on a vacuum created pair of -brane. One of them is shown to describe an AdS Schwarzschild spinning
black hole and the other is shown to describe a spinning black hole bound
state. It is argued that a D-instanton in a vacuum created anti D3-brane within
a pair may describe a quintessence. It may seen to incorporate a varying vacuum
energy density in a brane universe. We consider the effective curvature scalar
on to analyze torsion-less geometries on a vacuum created pair
of -brane. The emergent brane is shown to describe a
Schwarzschild and a Reissner-Nordstrom (RN) geometries in presence of extra
dimension(s).Comment: 20 pages, expanded discussion and added referenc
An X-ray view of quasars
I present an overview of observational studies of quasars of all types, with
particular emphasis on X-ray observational studies. The presentation is based
on the most popularly accepted unified picture of quasars - collectively
referred to as AGN (active galactic nuclei) in this review. Characteristics of
X-ray spectra and X-ray variability obtained from various X-ray satellites over
the last 5 decades have been presented and discussed. The contribution of AGN
in understanding the cosmic X-ray background is discussed very briefly. Attempt
has been made to provide up-to-date information; however, this is a vast
subject and this presentation is not intended to be comprehensive.Comment: Accepted for publication in the Bulletin of the Astronomical Society
of India (22 pages, 6 figures
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