1999 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/2909

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Aspects of gravitational clustering
(2015-03-01) Padmanabhan, T.
Several issues related to the gravitational clustering of collisionless dark matter in an expanding universe is discussed. The discussion is pedagogical but the emphasis is on semianalytic methods and open questions-rather than on well established results.
Bulk viscosity of strange quark matter in density dependent quark
(2015-03-01) Anand, J.D.; Chandrika Devi, N.; Gupta, V.K.; Singh, S.
COBE and global topology: An example of the application of the identified circles principle
(2015-03-01) Roukema, B.F.
Constraining curvature parameters via topology
(2015-03-01) Roukema, B.F.; Luminet, Jean-pierre
Correlations among global photometric properties of disk galaxies
(2015-03-01) Khosroshahi, Habib G.; Wadadekar, Yogesh; Kembhavi, A.K.
Deep optical observations at the position of PSR1706-44 with the VLT-UT1
(2015-03-01) Lundqvist, Peter; Sollerman, Jesper; Ray, Alak; Leibundgut, Bruno; Sutaria, Firoza
Derivation of the Maxwell equations and the relation between electric and magnetic charge
(2015-03-01) Singh, Parampreet; Dadhich, Naresh
Detection of gravitational waves using a network of detectors
(2015-03-01) Bose, Sukanta; Dhurandhar, S.V.; Pai, Archana
We formulate the data analysis problem for the detection of the Newtonian coalescing-binary signal by a network of laser interferometric gravitational wave detectors that have arbitrary orientations, but are located at the same site. We use the maximum likelihood method for optimizing the detection problem. We show that for networks comprising of up to three detectors, the optimal statistic is just the matched network-filter. Alternatively, it is simply a linear combination of the signal-to-noise ratios of the individual detectors. This statistic, therefore, can be interpreted as the signal-to-noise ratio of the network. The overall sensitivity of the network is shown to increase roughly as the square-root of the number of detectors in the network. We further show that these results continue to hold even for the restricted post Newtonian filters. Finally, our formalism is general enough to be extended, in a straightforward way, to address the problem of detection of such waves from other sources by some other types of detectors, eg., bars or spheres, or even by networks of spatially well-separated detectors.
Domain walls in kaluza-klein spacetime
(2015-03-01) Patel, L.K.; Dadhich, Naresh; Tikekar, R.
Three families of exact solutions of Einstein field equations are found. Each family contains three parameters. Two of these families represent thick domain walls in a five dimensional Kaluza-Klein spacetime.The dynamical behaviour of our models is briefly discussed. The spacetime in all the cases is found to be reflection symmetric with respect to the wall.
Dual spacetimes, mach’s principle and topological defects
(2015-03-01) Dadhich, Naresh
By resolving the Riemann curvature relative to a unit timelike vector into electric and magnetic parts, we define a duality transformation which interchanges active and passive electric. parts. It implies interchange of roles of Ricci and Einstein curvatures. 'Further by modifying the vacuum/flat equation we construct spacetimes dual to the Schwarzschild solution and flat spacetime. The dual spacetimes describe the original spacetimes with global monopole charge and global texture. The duality so defined is thus intimately related to the topologiccJ, defects ~nd also renders the Schwarzschild field asymptotically non-flat which augurs well with Mach's Principle.
Effective radii and color gradients in radio galaxies
(2015-03-01) Mahabal, Ashish; Kembhavi, A.K.; Mccarthy, P.J
We present de Vaucouleurs' effective radii in B and R bands for a sample of Molonglo Reference Catalogue radio galaxies and a control sample of normal galaxies. We use the ratio of the scale lengths in the two bands as an indicator to show that the radio galaxies tend to have excess of blue color in their inner region much more frequently than the control galaxies. We show that the scale length ratio is a useful indicator of radial color variation even when the conventional color gradient is too noisy to serve the purpose.
Electromagnetic duality in general relativity
(2015-03-01) Dadhich, Naresh
By resolving the Riemann curvature relative to a unit timelike vector into electric and magnetic parts, we consider duality relations analogous to the electromagnetic theory. It turns out that the duality symmetry of the Einstein action implies the Einstein vacuum equation without the cosmological term. The vacuum equation is invariant under interchange of active and passive electric parts giving rise to the same vacuum solutions but the gravitational constant changes sign. Further by modifying the equation it is possible to construct interesting dual solutions to vacuum as well as to flat spacetimes.
Evidence for filamentarity in the las campanas redshift survey
(2015-03-01) Bharadwaj, Somanath; Sahni, Varun; Sathyaprakash, B.S.; Shandarin, S.F.; Yess, Capp
Exact solutions for null fluid collapse in higher dimensions
(2015-03-01) Patel, L.K.; Dadhich, Naresh
A large family of inhomogeneous non-static spherically symmetric solutions of the Einstein equation for null fluid in higher dimensions has been obtained. It encompasses higher dimensional versions of many previously known solutions such as Vaidya, charged Vaidya and Husain solutions and also some new solutions representing global monopole or string dust. It turns out that physical properties of the solutions carry over to higher dimensions.
Faraday effect : A field theoretical point of view
(2015-03-01) Ganguly, Avijit K.; Konar, Sushan; Pal, Palash. B.
We analyze the structure of the vacuum polarization tensor in the presence of a background electromagnetic field in a medium. The most general gauge invariant structure contains many form factors. We use various discrete symmetries and crossing symmetry to constrain these form factors. From these symmetry arguments, we show why the vacuum polarization tensor has to be even in the background field when there is no background medium. Taking then the background field to be purely magnetic, we evaluate the vacuum polarization to linear order in it. The result shows the phenomenon of Faraday rotation, i.e., the rotation of the plane of polarization of a plane polarized light passing through this background. Finally, we calculate the amount of Faraday rotation in different kinds of media - non-relativistic, completely degenerate, and ultra-relativistic.
Formation of proto-quasar from magnetized accretion flows
(2015-03-01) Mangalam, A.
Galaxy clustering at Z~2 and halo radii
(2015-03-01) Roukema, B. F.; Valls-Gabaud, D.; Mobasher, B.; Bajtlik, Stanislaw
Generating lambda from the vacuum
(2015-03-01) Sahni, Varun
The close relationship between the cosmological constant and the vacuum has been emphasised in the past by Zeldovich amongst others. We briefly discuss different approaches to the cosmological constant issue including the possibility that A could be generated by vacuum polarization in a static Universe. Fresh possibilities occur in an expanding Universe. An Inflationary Universe generically leads to particle creation from the vacuum, the nature and extent of particle production depending upon the mass of the field and ~ts coupling to gravity. For ultra-light, non-minimally coupled scalar fields, particle production can be large and the resulting vacuum energy-momentum tensor will have the form of an effective cosmological constant. The Inflationary scenario therefore, could give rise to a Universe that is both flat and A-dominated, in agreement with observations.
Global monopole as dual-vacuum solution in kaluza-klein spacetime
(2015-03-01) Dadhich, Naresh; Patel, L.K.; Tikekar, R.
By application of the duality transformation, which implies interchange of active and passive electric parts of the Riemann curvature (equivalent to interchange of Ricci and Einstein tensors) it is shown that the global monopole solution in the Kaluza-Klein spacetime is dual to the corresponding vacuum solution. Further we also obtain solution dual to flat space which would in general describe a massive global monopole in 4-dimensional Euclidean space and would have massless limit analogus to the 4-dimensional dual-flat solution.
Gravoelectric-dual of the kerr solution
(2015-03-01) Dadhich, Naresh; Patel, L.K.
By decomposing the Riemann curvature into electric and magnetic parts, we define the gravoelectric duality transformation by interchange of active and passive electric parts which amounts to interchange of the Ricci and Einstein tensors. It turns out that the vacuum equation is duality-invariant. We obtain solutions dual to the Kerr solution by writing an effective vacuum equation in such a way that it still admits the Kerr solution but is not duality invariant. The dual equation is then solved to obtain the dual-Kerr solution which can be interpreted as the Kerr black hole sitting in a string dust universe.