1992 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/2663
Browse
9 results
Search Results
Item Quantum effects near a point mass in 2+1 dimensional gravity(2014-11-26) Souradeep, Tarun; Sahni, VarunItem The search for gravitational waves(2014-11-26) Dhurandhar, S.V.The direct detection of gravitational waves is one of the most challenging problems in experimental physics today. Sustained efforts have led to impressive advances on both theoretical and experimental fronts. This article first deals with the theoretical aspects of gravitational waves and then continues on to describe the detectors in vogue, the present status and various gravitational waves sources.Item Choice of filters for the detection of gravitational waves from coalescing binaries II: detection in coloured noise(2014-11-25) Dhurandhar, S.V.; Sathyaprakash, B.S.We discuss the problem of detecting gravitational waves signals embedded in coloured noise from coalescing binary systems. The signal is assumed to be Newtonian and matched filtering techniques are employed to filter out the signal. The problem is discussed at first for a general power spectral density of the noise and then specific numerical results are obtained for the standard recycling case. Since the signal parameters are unknown, a bank of filters is needed to carry out the signal detection. The number of filters in a bank , the spacing between filter etc. is obainted for different values of minimum strength of the signal relative to the threshold. We also present an approximate analytical formula which relates the spacing between filter to the minimum strength. Finally we discuss the problem of detection probabilities given a data train.Item Constraints on the shape of the density spectrum from COBE and galaxy surveys(2014-11-23) Padmanabhan, T.; Narasimha, D.Item Zeldovich approximation and the probability distribution for the smoothed density field in the nonlinear regime(2014-11-23) Padmanabhan, T.; Subramanian, KandaswamyThe study of large-scale structure in the Universe is often based on the observed density distribution of matter smoothed by a suitable filter function. The probability distribution for this smoothed density field in the nonlinear regime is studied using the Zeldovich approximation. When the shear term of the velocity field is not too large, one can obtain a reasonably good analytic approximation to this probability distribution. The properties of this distribution are discussed and compared with other attempts along similar lines.Item A parallel algorithm for filtering gravitational waves from coalescing binaries(2014-11-23) Sathyaprakash, B.S.; Dhurandhar, S.V.Coalescing binary stars are perhaps the most promising sources for the observation of gravitational waves with laser interferometric gravity wave detectors. The waveform from these sources can be predicted with sufficient accuracy for matched filtering techniques to be applied. In this paper we present a parallel algorithm for detecting signals from coalescing compact binaries by the method of matched filtering. We also report the details of its implementation on a 256-node connection machine consisting of a network of transputers. The results of our analysis indicate that parallel processing is a promising approach to on-line analysis of data from gravitational wave detectors to filter out coalescing binary signals. The algorithm described is quite general in that the kernel of the algorithm is applicable to any set of matched filters.Item On gravitational charge of stationary spacetimes(2014-11-23) Dadhich, NareshWe point out that ours is a definition of gravitational charge and not of quasilocal mass [1] we have defined gravitational charge as the flux of effective gravitational acceleration across a closed 2- surface. It turns out that tidal force can change its sense from convergence to divergence outside the horizon for suitable range of values of rotation and electric charge parameters of the black hole.Item On active and passive gravitational mass of fluid sphere(2014-11-23) Dadhich, NareshItem Post-COBE prediction for inflationary gravity wave and density perturbation spectra(2014-11-22) Sahni, Varun;Souradeep,TarunWe assess the relative contribution to the COBE - measured microwave anisotropy arising both from relic gravity waves as well as primordial density perturbations originating during inflation. We show that the gravity wave contribution to the CMBR anisotropy depends sensitively upon n -- the primordial spectral index ($\dk^2 propto k^n$), increasing as n deviates from a Harrison - Zeldovich spectrum (n = 1). As a result, for n<0.84 the contribution from gravity waves towards δT/T is greater than the corresponding contribution from density perturbations, whereas for n>0.84 the reverse is true. (n=0.84 corresponds to an expansion index p=13.5 in models with power-law inflation a∝tp. ) Our results show that for a scale-invariant Harrison-Zeldovich spectrum generated by chaotic inflation, gravity waves contribute approximately 24% to the CMBR anisotropy measured by COBE. Applying our results to the cold dark matter scenario for galaxy formation, we find that in general CDM models with tilted power spectra (n<1), require the biasing parameter to be greater than unity, on scales of 16h−150Mpc. We also obtain an expression for the COBE - normalised amplitude and spectrum of the stochastic gravity wave background and compare it with the sensitivity of planned laser-interferometer gravity wave detectors.