1993 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/2786
Browse
Item Algorithm for optimally distributing quantized load on transputers with unequal speed: An application to the detection of gravitational wave signals from coalescing binaries(2015-01-13) Pitre, Sangita. N.; Dhurandhar, S.V.In a parallel computing system, we work with a network of a large number of processors wherein the performance characteristics each processer may have are different. This leads to a situation that when there is equal load on all the processer, some complete the job before the others. To make the optimum use of the available computing facility and optimise on time, it is necessary to balance the load on the processers according to there characteristics like speed etc. Here we present an algorithm to optimse to on ‘ time ‘ when difference processer have difference speed and the load is quantised in integral multiples of a given unit of load. The algorithm distribute the load in such a manner that all the processer work optimally and the processing time is minimal. The optimal distribution of the load is achived by employing the well known bisection technique for finding the rots of an equation. We discuss this algorithm in the context of our application for filtering the coalescing binary gravitational wave signals. Numerical result are finally discussed for the 64 transputer machine ( PARAM ) .Item Baryonic content of galactic halos and constraints on models for structure formation(2015-01-17) Padmanabhan, T.; Subramanian, K.Item Cosmology today-models and constraints(2015-01-17) Padmanabhan, T.Item Electric charge from spontaneous breaking of symmetry(2015-01-13) Gupta, Patrick DasThe duality symmetry present in the Maxwell equations admitting magnetic charges is gauged using a complex scalar field. In this new model, electromagnetic charge arises because of a "Yukawa" type coupling of the matter with the scalar field. Considering an interacting Dirac field we show that spontaneous symmetry breaking in the scalar field sector leads at low energy to the reduction of this theory to the usual electrodynamics without magnetic charges. The notion of electric charge as a coupling constant arises very naturally in this model. Higgs mechanism in this model gives rise to the existence of a scalar and a vector field, both real and massive.Item The evolution voids in the adhesion approximation(2015-01-17) Sahni, Varun; Sathyaprakash, B.S.; Shandarin, S.F.Item Geometric phase in vacuum instability: Applications in quantum cosmology(2015-01-13) Datta, Dhurjati PrasadThere different methods viz. i) a perturbative analysis of the schrodinger equation ii) abstract differential geometric method and iii) a semiclassical reduction of the Wheeler Dewitt equation, relating pancharatnam phase to vacuum instability are discussed. An improved semiclassical reduction is also shown to yield the correct zeroth order semiclassical Einstein equations with backreaction. This constitutes an extension of our earlier discussion on the topic.Item Gravity wave from mini-creation events(2015-01-13) Dasgupta, P.; Narlikar, J. V.This paper examines the possibility of testing the hypothesis recently proposed by some authors that, instead of the one-shot creation of the entire Universe in a big bang, creation of matter takes place in finite bursts at random in a Universe that is without a beginning and whose expansion on the large scale is as given by the steady state model. It is argued that if the creation events are anisotropic then they generate gravitational waves. Calculations are given to show that a laser interferometric detector of the UGO type would easily detect an event that generates -100-1000M0 .Further, the cosmological gravitational wave background generated by the minicreationevents is compared with the limits set by the analysis of the arrival time of pulses from millisecond pulsars. The existing data place severe constraints on the mass and anisotropies of the mini-creation events.Item Isolated pairs of spiral galaxies – A statistical study of far infrared and microwave characteristics(2015-01-13) Venugopal, V.R.; Narasimhan, K.S.V.S.A statistical study of the infrared and microwave luminosities of a sample of isolated pairs of spiral galaxies and a comparison sample of non- interacting galaxies selected from the lists given by Wunderlich and Klein (1991) does not reveal any significant between the two samples.Item Magnetic charges and local duality symmetry - II(2015-01-13) Gupta, Patrick DasThe notion of magnetic charges is intimately linked with the global duality symmetry exhibited by the extended Maxwell equation. We show that duality symmetry is meaning only in 3+1 dimensional space- times, implying thereby that magnetic monopoles as fundamental particle can be postulated only 3+1 dimensions. We also study the consequences of elevating the status of duality symmetry to a local symmetry. Local duality symmetry is achieved by introducing a complex scalar field in the theory. The new theory is generalization of the extended Maxwell theory. In this formalism, the electromagnetic charges arise due to a spontaneous symmetry breaking. By choosing a suitable gauge one can recover ordinary electrodynamics without the magnetic charges.Item A model for the declining rotation curves of cluster spirals(2015-01-17) Valluri, MonicaNumerical studies have shown that mean tidal field in clusters of galaxies can cause a significant increase in the planar velocity dispersions of stars, and gas clouds in disks of spiral galaxies. Since the perturbation caused by cluster tidal field are generally weak and fairly symmetric, the stellar distribution of galaxies would not necessary show obvious signs of tidal disturbance. In this paper it is shown that the increased non-circular velocities of stars can result in symmetric decline (at large radii) of the rotation curves of the perturbed spiral galaxies. This decline result from the well known phenomenon of the “asymmetric drift” a high velocity dispersion stellar population. This suggest that the observation of the declining rotation curves of spiral galaxies in clusters do not necessarily imply that their dark matter halos have been tidally truncated as is generally assumed.Item Nonlinear evolution of density perturbation(2015-01-17) Bagla, J. S.; Padmanabhan, T.From the epoch of recombination ( Z ≈103 ) till today, the typical density contrasts have grown by a factor of about 106 in Friedmann universe with Ω = 1. However, during the same epoch the typical gravitational potential has grown only by a factor of order unity. We present theoretical arguments explaining the origin of this approximate constancy of gravitational potential. This fact can be exploited to provide a new, powerful, approximation scheme to study the formation of nonlinear structures in the universe. The essential idea of this method is to evolve the initial distribution of particles using a gravitational potential frozen in time. We carry out this scheme for several standard models including the CDM and HDM and show that the results match quite well with those obtained by exact Numerical simulations. We compute different statistical measures of clustering and compare them for the description of nonlinear evolution. This approximation also provides valuable insight into understanding various features of nonlinear evolution; for example, it provides a simple explanation as to why pancakes remain thin during the evolution even in the absence of any artificial, adhesion-like, damping terms. We also compare this approximation with other schemes like Zeldovich approximation and frozen-flow. Our procedure has a far greater range of validity than the Zeldovic h approximation since it can handle motion across (and inside) caustic properly. Unlike in frozen-flow, actual shell-crossing does occur in the frozen-potential approximation; hence it provides a far more accurate description of the velocity field compared to frozen flow approximation.Item Nonlinear evolution of density perturbations using approximate constancy of gravitational potential(2015-01-13) Bagla, J. S.; Padmanabhan, T.Item Nonlinear sigma model for inflation scenarios.II(2015-01-17) Chervon, S.V.In this paper the self –gravitating nonlinear sigma model is considered in the context of inflation scenarios as an alternative to the self-interacting scalar field theory. The complete set of new exact solutions for the two-component sigma model in the frame work of spatially flat friendmann- Robertson- Walker and de sitter universes is obtained.Item On singularity free cosmological model(2015-01-13) Dadhich, Naresh; Tikekar, R.; Patel, L.K.Item On the closure of the universe: A note on the cosmological constant(2015-01-17) Masafumi, Seriu,Item On the relation between causality and topology in the semiclassical universe(2015-01-13) Seriu, Masafumi; Singh, T. P.We systematically derive a series of validity conditions for semiclassical gravity and deduce a strong restriction on the possible topology of the semiclassical universe founded on the path-integral formalism. We begin with the investigation of the fundamental setting of quantum gravity. We show that, in order to obtain the causal semiclassical Einstein equation at the later stage of the universe, we have to regard the in-in path-integral formalism as fundamental in quantum gravity. We then perform the stationary phase approximation for the gravity mode. From the first variation of the phase , we obtain a series of validity conditions of semiclassical gravity in a completely general manner.Item On the smallness of the cosmological constant(2015-01-17) Masafumi, Seriu,We investigate the possible values of the cosmological constant allowed by quantum cosmology. If we formulate quantum cosmology respecting the causal nature of fundamental equations in the semiclassical regime of the universe, then any classical universe should have at least one symmetric surface on which every component of the extrinsic curvature vanishes. Combined with the Hamiltonian constrain, this implies that the allowed values of the cosmological constant are bounded from above. Applying this argument to the Robertson- Walker Universe, we obtain the theoretical upperbound for the cosmological constant, being of order (H0 / c)2 . This upperbound can also be interpreted as being determined by the adiabatic Schwarzshild radius of the whole universe. In this way, the question as to why the cosmological constant is so small is reduced to the question, why there is so much matter in our universe.Item Performance of Newtonian filters in the detection of gravitational radiation from coalescing binaries(2015-01-13) Balasubramanian, R.; Dhurandhar, S.V.Post – Newtonian corrections to the gravitational waveform emitted by coalescing binaries have been found to lead to a secular phase accumulation error as compared with the signals calculated in the Newtonian approximation. The matched filtering process which relies on the correlation between the correlation between the signal and the filter is extremely sensitive to errors in phase. We explore the possibility of compensating for the phase difference caused by the post-Newtonian terms by allowing for a shift in the Newtonian filter parameters. We find that, on the average, we lose by about 30% in the correlation.Item Response of the interferometric antenna to gravitational radiation from pulsars(2015-01-13) Jotania, Kanti; Dhurandhar, S.V.We present here a full calculation of the response of a laser interferometric gravitational wave detector on which gravitational radiation from a continuous source is incident. The observation time is taken to be of the order of few months. The long observation time implies that the motion of the detector is important and must be included in the response as a modulation effect. For simplicity we consider only two motions of the Earth , namely the rotation of the Earth about axis and the orbital motions about the sun. The orbit is assumed to be circular. We consider the detector to be situated and oriented arbitrarily on the Earth, except that we assume the arms of the detector must lie in the tangent plane to the Earth at the point where the detector is situated. The gravitational wave incident on the detector is assumed to be a plane wave having arbitrary direction and polarization. We also present here the computation of the quadrupole wave form of a typical continuous source – a pulsar-which is modelled as an almost spherical object of uniform density, spinning about an arbitrary axis with uniform angular velocity. We use techniques of spherical tensors and Gel’fandfunction developed in the literature to compute the waveformItem Scaling properties of gravitational clustering in the non-linear regime(2015-01-13) Nityananda, R.