2005 (IPP)
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Item Anomalous obsorption in H2Co molecule(2005-12-01) Chandra, Suresh; Musrif, P. G.; Shinde, S. V.Item Winding Road to Quantum Gravity(2005-09-01) Ashtekar, AbhayThe goal of this article1 is to present a brief history of quantum gravity for the general readership of Current Science which is much broader than the community of research physicists. While familiarity with basic ideas and notions of contemporary physics is assumed, technicalities are kept to a minimum and use of equations is avoided. Rather, the emphasis is on providing a coherent picture of the evolution of ideas and the current status of the subject.Item VLT-UVES survey for molecular hydrogen in high-redshift damped Lyman-alpha systems: Physical conditions in the neutral gas(2005-06-01) Srianand, R.; Petitjean, Patrick; Ledoux, C´edric; et al.We study the physical conditions in damped Lyman-α systems (DLAs), using a sample of 33 systems toward 26 QSOs acquired for a recently completed survey of H2 by Ledoux et al. (2003). We use the column densities of H2 in different rotational levels, together with those of C i, C i ∗, C i ∗∗, C ii ∗ and singly ionized atomic species to discuss the kinetic temperature, the density of hydrogen and the electronic density in the gas together with the ambient UV radiation field. Detailed comparisons are made between the observed properties in DLAs, the interstellar medium (ISM) of the Galaxy, the large and small Magellanic clouds (LMC and SMC).The mean kinetic temperature of the gas corresponding to DLA subcomponents in which H2 absorption line is detected, derived from the ortho-to-para ratio (153±78 K), is higher than that measured in the ISM (77±17 K) and the Magellanic clouds (82±21 K). Typical pressure in these components (corresponding to T = 100−300 K and nH = 10−200 cm−3), measured using C i fine-structure excitation, are higher than what is measured along ISM sightlines. This is consistent with the corresponding higher values for N(H2,J=2)/N(H2,J=0) seen in DLAs. From the column densities of the high-J rotational levels, we derive that the typical radiation field in the H2 bearing components is of the order of or slightly higher than the mean UV field in the Galactic ISM. Determination of electron density in the gas with H2 and C i show the ionization rate is similar to that of a cold neutral medium (CNM) in a moderate radiation field. This, together with the fact that we see H2 in 13-20% of the DLAs, can be used to conclude that DLAs at z > 1.9 could contribute as much as 50% star formation rate density seen in Lyman break galaxies (LBGs).C ii ∗ absorption line is detected in all the components where H2 absorption line is seen. The excitation of C ii in these systems is consistent with the physical parameters derived from the excitation of H2 and C i. We detect C ii ∗ in about 50% of the DLAs and therefore in a considerable fraction of DLAs that do not show H2. In part of the later systems, physical conditions could be similar to that in the CNM gas of the Galaxy. However, the absence of C i absorption line and the presence of Al iii absorption lines with a profile similar to the profiles of singly ionized species suggest an appreciable contribution from warm (WNM) and/or partially ionized gas. The absence of H2, for the level of metallicity and dust depletion seen in these systems, are consistent with low densities (i.e nH 6 1 cm−3) for a radiation field similar to the mean Galactic UV field.Item Understanding Our Universe : Current Status and Open Issues(2005-03-01) Padmanabhan, T.Last couple of decades have been the golden age for cosmology. High quality data confirmed the broad paradigm of standard cosmology but have thrusted upon us a preposterous composition for the universe which defies any simple explanation, thereby posing probably the greatest challenge theoretical physics has ever faced. Several aspects of these developments are critically reviewed, concentrating on conceptual issues and open questions.Item Time-Delay interferometry(2005-07-01) Tinto, Massimo; Dhurandhar, SanjeevEqual-arm interferometric detectors of gravitational radiation allow phase measurements many orders of magnitude below the intrinsic phase stability of the laser injecting light into their arms. This is because the noise in the laser light is common to both arms, experiencing exactly the same delay, and thus cancels when it is differenced at the photo detector. In this situation, much lower level secondary noises then set overall performance. If, however, the two arms have different lengths (as will necessarily be the case with space-borne interferometers), the laser noise experiences different delays in the two arms and will hence not directly cancel at the detector. In order to solve this problem, a technique involving heterodyne interferometry with unequal arm lengths and independent phase-difference readouts has been proposed. It relies on properly time-shifting and linearly combining independent Doppler measurements, and for this reason it has been called Time-Delay Interferometry (or TDI). This article provides an overview of the theory and mathematical foundations of TDI as it will be implemented by the forthcoming space-based interferometers such as the Laser Interferometer Space Antenna (LISA) mission. We have purposely left out from this first version of our “Living Review” article on TDI all the results of more practical and experimental nature, as well as all the aspects of TDI that the data analysts will need to account for when analyzing the LISA TDI data combinations. Our forthcoming “second edition” of this review paper will include these topics.Item Statistical isotropy of CMB anisotropy from WMAP(2005-02-01) Souradeep, Tarun; Hajian, AmirThe statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003. The Bipolar Power Spectrum (BiPS) is estimated for the full sky CMB anisotropy maps of the first year WMAP data. The method allows us to isolate regions in multipole space and study each region independently. This search shows no evidence for violation of statistical isotropy in the first-year WMAP data on angular scales larger than that corresponding to l ≈ 60 .Item Solutions of Certain Types of Linear and Nonlinear Diffusion-Reaction Equations in One Dimension(2005-01-01) Kaushal, R. S.With a view to having further insight into the mathematical content of the non-Hermitian Hamiltonian associaterd with the diffusion-reaction (D-R) equation in one dimension, we investigate (a) the solitary wave solutions of certain types of its nonlinear versions, and (b) the problem of real eigenvalue spectrum associated with its linear version or with this class of non-Hermitian Hamiltonians. For the case (a) we use the standard techniques to handle the quadratic and cubic nonlinearities in the D-R equation whereas for the case (b) a newly proposed method, based on an extended complex phase space, is employed. For a particular class of solutions, an Ermakov system of equations is also found for the linear case. Further, corresponding to the ’classical’ version of the above one-dimensional complex Hamiltonian, an equivalent integrable system of two, two-dimensional real Hamiltonians is suggested.Item Scattering properties and composition of cometary dust(2005-04-01) Gupta, Ranjan; Vaidya, D.B.; Dobbie, J.S.; et al.Composition of the Comet dust obtained by the dust impact analyzer on the Halley probes indicated that the comet dust is a mixture of silicate and carbonaceous material. The collected interplanetary dust particles (IDP’s) are fluffy and composite, having grains of several different types stuck together. Using Discrete Dipole Approximation (DDA) we study the scattering properties of composite grains. In particular, we study the angular distribution of the scattered intensity and linear polarization of composite grains. We assume that the composite grains are made up of a host silicate sphere/spheroid with the inclusions of graphite. Results of our calculations on the composite grains show that the angle of maximum polarization shifts, and the degree of polarization varies with the volume fraction of the inclusions. We use these results on the composite grains to interpret the observed scattering in cometary dust.Item Probabitlity for Primordial Black holes Pair in 1/R Gravity(2005-08-01) Paul, Dilip; Paul, B. C.The probability for quantum creation of an inflationary universe with a pair of black holes in 1/R - gravitational theory has been studied. Considering a gravitational action which includes a cosmological constant (Λ) in addition to δ R−1 term, the probability has been evaluated in a semiclassical approximation with Hartle-Hawking boundary condition. We obtain instanton solutions determined by the parameters δ and Λ satisfying the constraint δ ≤ 4Λ23 . However, we note that two different classes of instanton solutions exists in the region 0 < δ < 4Λ23 . The probabilities of creation of such configurations are evaluated. It is found that the probability of creation of a universe with a pair of black holes is strongly suppressed with a positive cosmological constant except in one case when 0 < δ < Λ2. It is also found that gravitational instanton solution is permitted even with Λ = 0 but one has to consider δ < 0. However, in the later case a universe with a pair of black holes is less probable.Item Reliability checks on the Indo-Us stellar spectral library using artificial neural networks and principal component analysis(2005-09-01) Singh, Harinder P.; Gupta, Ranjan