2001 (IPP)

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About the Dunham coefficients Y20 and Y11 for diatomic molecules
(2001-01-12) Sharma, A. K.; Chandra, S.
For a diatomic molecule, when the Dunham coefficients Y20 is negative, all fea- tures of potential-energy curve can be reproduced. When Y20 is positive; it is not possible to reproduce all features of the potential-energy curve. However, turning points for some lower vibrational states can be obtained.
Accretion powered spherical wind in general relativity
(2001-04-14) Das, Tapas K.
Using full general relativistic calculations, we investigate the possibility of generation of mass outﬂow from spherical accretion onto non-rotating black holes. Introducing a relativistic hadronic-pressure-supported steady, standing, spherically-symmetric shock surface around a Schwarzschild black hole as the eﬀective physical barrier that may be responsible for the generation of spherical wind, we calculate the mass outﬂow rate R ˙ m in terms of three accretion parameters and one outﬂow parameter by simultaneously solving the set of general relativistic hydrodynamic equations describing spherically symmetric, transonic, polytropic accretion and wind around a Schwarzschild black hole. Not only do we provide a suﬃciently plausible estimation of R ˙ m, we also successfully study the dependence and variation of this rate on various physical parameters governing the ﬂow. Our calculation indicates that independent of initial boundary conditions, the baryonic matter content of this shock-generated wind always correlates with post-shock ﬂow temperature.
Algebraic approach to time-delay data analysis for LISA
(2001-12-20) Dhurandhar, Sanjeev; Nayak, K. R.; Vinet, J-Y.
Cancellation of laser frequency noise in interferometers is crucial for attaining the requisite sensitivity of the triangular 3-spacecraft LISA conﬁguration. Raw laser noise is several orders of magnitude above the other noises and thus it is essential to bring it down to the level of other noises such as shot, acceleration, etc. Since it is impossible to maintain equal distances between spacecrafts, laser noise cancellation must be achieved by appropriately combining the six beams with appropriate time-delays. It has been shown in several recent papers that such combinations are possible. In this paper, we present a rigorous and systematic formalism based on algebraic geometrical methods involving computational commutative algebra, which generates in principle all the data combinations cancelling the laser frequency noise. The relevant data combinations form the ﬁrst module of syzygies, as it is called in the literature of algebraic geometry. The module is over a polynomial ring in three variables, the three variables corresponding to the three time-delays around the LISA triangle. Speciﬁcally, we list several sets of generators for the module whose linear combinations with polynomial coeﬃcients generate the entire module. We ﬁnd that this formalism can also be extended in a straight forward way to cancel Doppler shifts due to optical bench motions. The two modules are infact isomorphic. We use our formalism to obtain the transfer functions for the six beams and for the generators. We speciﬁcally investigate monochromatic gravitational wave sources in the LISA band and carry out the maximisiation over linear combinations of the generators of the signal-to-noise ratios with the frequency and source direction angles as parameters.
Anisotropy dissipation in brane-world inflation
(2001-02-14) Maartens, Roy; Sahni, Varun; Saini, Tarun Deep
We examine the behavior of an anisotropic brane-world in the presence of inﬂationary scalar ﬁelds. We show that, contrary to naive expectations, a large anisotropy does not adversely aﬀect inﬂation. On the contrary, a large initial anisotropy introduces more damping into the scalar ﬁeld equation of motion, resulting in greater inﬂation. The rapid decay of anisotropy in the brane-world signiﬁcantly increases the class of initial conditions from which the observed universe could have originated. This generalizes a similar result in general relativity. A unique feature of Bianchi I brane-world cosmology appears to be that for scalar ﬁelds with a large kinetic term the initial expansion of the universe is quasi-isotropic. The universe grows more anisotropic during an intermediate transient regime until anisotropy ﬁnally disappears during inﬂationary expansion.
Astrophysical consequences of diquark formation on the surface of strange star
(2001-05-12) Dey, Mira; Sinha, Monika; Ray, Subharthi
Compactness of some stars is explained if they are strange stars (SS) as shown by Dey et al.(1998) (D98) and Li et al. (1999a,b). In D98, a realistic potential was used in a Fock mean eld approximation within Dirac phe- nomenology, thereby simplifying the spinorial structure of the quarks. Using the plane wave states for the beta equi- librated u, d and s quark Fermi seas from D98 and the conventional spin dependent force between these quarks, we now nd energy lowering in some speci c spin-aligned states. This is a short range pairing between quarks of dif- ferent ﬂavours and may lower the energy by several MeV for each diquark pair. The accretion driven X-ray and γ ray bursts in com- pact objects are believed to be due to thermonuclear or some other explosions which are short lived. These may in fact destroy the spin alignment of the quarks if these stars are SS. The subsequent alignment and production of copious diquark pairing may produce su cient energy to produce recurrent very long bursts seen in some such stars. The long time involved in these processes, we claim, is due to the weak interactions which are responsible for the equilibration of strange quark matter. In such a the case the elusive properties of some of the most massive objects in nature, the compact stars, can be accounted for by spin alignment of pairs of the smallest components of matter, - namely the quarks.
BeppoSAX observation of the rich cluster of galaxies Abell 85
(2001-01-06) Lima Neto, G. B.; Pislar, V.; Bagchi, Joydeep
We report the observation of the Intra-Cluster Medium (ICM) of Abell 85 by the X-ray satellite Bep- poSAX. We have both analysed the spectrum obtained in the central 8 arcmin circular region centred on the Very Steep Spectrum Radio Source (VSSRS) and the spec- tra from a number of sub-regions. Analysis of the spec- tra allowed us to independently obtain new estimates of the temperature, metallicity and line-of-sight hydro- gen density column, both globally (T = 6.6 ± 0.3 keV, Z = 0.38 ± 0.06Z⊙ and NH = 5.5+0.9 −0.71020cm−2) and lo- cally. These measures are in good agreement with previ- ous measures based on ROSAT and ASCA data. In the region of the VSRSS, we have tried to disentangle the thermal from the non-thermal X-ray emission. Although we could not do this unambiguously, we have nonethe- less estimated the extended magnetic ﬁeld using the radio spectrum available for this region.We obtain a lower limit intensity of 0.9µG, consistent with our previous estimate. We also derive α-elements/iron abundance ratios that turn out to be higher than 1. Such a result tends to support the burst model for elliptical galaxies, where a strong galac- tic wind develops early in the galaxy history and type II supernovae (SN) may have the main role in the enrich- ment of the ICM. A two-temperature ICM model was ﬁt- ted in the central region yielding a main component with roughly the mean cluster temperature and a cooler com- ponent with temperature less than 0.1 keV.
Binned cosmic microwave background anisotropy power spectra : Peak location
(2001-02-15) Podariu, Silviu; Souradeep, Tarun; Gott, J. Richard; et al.
We use weighted mean and median statistics techniques to combine individual cosmic microwave background (CMB) anisotropy detections and determine binned, multipole- space, CMB anisotropy power spectra. The resultant power spectra are peaked. The derived weighted-mean CMB anisotropy power spectrum is not a good representation of the individual measurements in a number of multipole-space bins, if the CMB anisotropy is Gaussian and correlations between individual measurements are small. This could mean that some observational error bars are underestimated, possibly as a consequence of undetected systematic eﬀects. Discarding the most discrepant 5% of the measure- ments alleviates but does not completely resolve this problem. The median-statistics power spectrum of this culled data set is not as constraining as the weighted-mean power spectrum. Nevertheless it indicates that there is more power at multipoles ℓ ∼ 150 − 250 than is expected in an open cold dark matter (CDM) model, and it is more consistent with a ﬂat CDM model. Unlike the weighted-mean power spectrum, the median-statistics power spectrum at ℓ ∼ 400 − 500 does not exclude a second peak in the ﬂat CDM model.
Collisional rates for vib-rotational transitions in diatomic molecules
(2001-06-24) Chandra, S.; Sharma, A. K.
A number of diatomic molecules have been found in vibrationally excited states in several cosmic objects. The molecules in vibrationally excited states provide valuable information about the physical conditions prevailing near star forming regions and in circumstellar envelopes of late-type stars. To analyze the spectrum of such molecules, some of the important parameters required are the collisional rate coe cients for vib-rotational transitions in the molecule. Currently, knowledge of collisional rate coe cients is very poor. Here, we discuss a method for calculating the collisional rate coe cients for vib-rotational transitions in a diatomic molecule, where the colliding partner H2 is considered as a structureless particle. This method is quite good for high temperatures (usually found in star-forming regions and in circumstellar envelopes of late-type stars), but may be questioned for low temperatures. As an example, calculations for the CS molecule at 500 K for three vibrational states are presented.
Combining general relativity and quantum theory : points of conflict and contact
(2001-09-12) Padmanabhan, T.
The issues related to bringing together the principles of general relativity and quantum theory are discussed. After brieﬂy summarising the points of conﬂict between the two formalisms I focus on four speciﬁc themes in which some contact has been established in the past between GR and quantum ﬁeld theory: (i) The role of planck length in the microstructure of spacetime (ii) The role of quantum eﬀects in cosmology and origin of the universe (iii) The thermodynamics of spacetimes with horizons and especially the concept of entropy related to spacetime geometry (iv) The problem of the cosmological constant.
Computational cost for detecting inspiraling binaries using a network of laser interferometric detectors
(2001-08-15) Pai, A.; Bose, Sukanta; Dhurandhar, Sanjeev
We extend a coherent network data-analysis strategy developed earlier for detecting Newtonian waveforms to the case of post-Newtonian (PN) waveforms. Since the PN waveform depends on the individual masses of the inspiraling binary, the parameter-space dimension increases by 1 from that of the Newtonian case. We obtain the number of templates and estimate the computational costs for PN waveforms: For a lower mass limit of 1M⊙, for LIGO-I noise, and with 3% maximum mismatch, the online computational speed requirement for single detector is a few Gﬂops; for a two-detector network it is hundreds of Gﬂops and for a three-detector network it is tens of Tﬂops. Apart from idealistic networks, we obtain results for realistic networks comprising of LIGO and VIRGO. Finally, we compare costs incurred in a coincidence detection strategy with those incurred in the coherent strategy detailed above
Consequences on some dark energy-candidates from SN 1997ff
(2001-07-28) Vishwakarma, R. G.
We examine the status of various dark energy-models in light of the recently observed SN 1997ﬀ at z ≈ 1.7. The modiﬁed data still ﬁt a pure cosmological constant Λ or a quintessence with an equation of state similar to that of Λ. The kinematical Λ-models, Λ ∼ S−2 and Λ ∼ H2 , also ﬁt the data reasonably well and require less dark energy density (hence more matter energy density) than is required by the constant Λ-model. However, the model Λ ∼ S−2 with low energy density becomes unphysical as it cannot accommodate higher redshift objects. We also examine an alternative explanation of the data, viz., the absorp- tion by the intervening whisker-like dust and ﬁnd that the quasi-steady state model and the FRW model Ωm0 = 0.33, without any dark energy also ﬁt the data reasonably well. We notice that the addition of SN 1997ﬀ to the old data has worsened the ﬁt to most of the models, except a closed FRW model with a constant Λ and a closed quintessence-model with ωφ = −0.82, and the models have started departing from each other as we go above z = 1. However, to make a clear discrimination possible, a few more supernovae with z > 1 are required. We have also calculated the age of the universe in these models and ﬁnd that, in the models with a constant Λ, the expansion age is uncomfortably close to the age of the globular clusters. Quintessence-models show even lower age. The kinematical Λ-models are, however, interesting in this con- nection (especially the model Λ ∼ H2 ), which give remarkably large age of the universe.
Consequences on variable /\ - models from distant type Ia supernovae and compact radio sources
(2001-02-20) Vishwakarma, R. G.
We study the magnitude-redshift relation for the Type Ia super- novae data and the angular size-redshift relation for the updated compact radio sources data (from Gurvits et al) by considering four variable Λ-models: Λ ∼ S−2 , Λ ∼ H2 , Λ ∼ ρ and Λ ∼ t −2 . It is found that all the variable Λ-models, as well as the constant Λ- Friedmann model, ﬁt the supernovae data equally well with χ2 /dof ≈ 1 and require non-zero, positive values of Λ and an accelerating expansion of the universe. The estimates of the density parameter for the variable Λ-models are found higher than those for the constant Λ-Friedmann model. From the compact radio sources data, it is found, by assuming the no- evolution hypothesis, that the Gurvits et al’ model (Friedmann model with Λ = 0) is not the best-ﬁtting model for the constant Λ case. The best-ﬁtting Friedmann model (with constant Λ) is found to be a low density, vacuum- dominated accelerating universe. The ﬁts of this data set to the (variable, as well as, constant Λ-) models are found very good with χ2 /dof ≈ 0.5 and require non-zero, positive values of Λ with either sign of the deceleration parameter. However, for realistic values of the matter density parameter, the only interesting solutions are (a) estimated from the supernovae data: the best-ﬁt solutions for the ﬂat models (including the constant Λ case); (b) estimated from the radio sources data: the global best-ﬁt solutions for the models Λ ∼ H2 and Λ ∼ ρ, the best-ﬁt solution for the ﬂat model with Λ = constant and the Gurvits et al’ model. It is noted that, as in the case of recent CMB analyses, the data sets seem to favour a spherical universe (k > 0).
Cosmic inventory of energy densities : issues and concerns
(2001-02-10) Padmanabhan, T.
The dynamics of our universe is characterised by the density parameters for cos- mological constant (ΩV ), nonbaryonic darkmatter(Ωwimp), radiation (ΩR) and baryons (ΩB). To these parameters — which describe the smooth background universe — one needs to add at least another dimensionless number (∼ 10−5) characterising the strength of primordial ﬂuctuations in the gravitational potential, in order to ensure formation of structures by gravi- tational instability. I discuss several issues related to the description of the universe in terms of these numbers and argue that we do not yet have a fundamental understanding of these issues
Cosmic Microwave Background Anisotropy Measurement from Python V
(2001-03-01) Coble, Kim; Dodelson, S.; Dragovan, Mark; et al.
We analyze observations of the microwave sky made with the Python exper- iment in its ﬁfth year of operation at the Amundsen-Scott South Pole Station in Antarctica. After modeling the noise and constructing a map, we extract the cosmic signal from the data. We simultaneously estimate the angular power spectrum in eight bands ranging from large (ℓ ∼ 40) to small (ℓ ∼ 260) angular scales, with power detected in the ﬁrst six bands. There is a signiﬁcant rise in the power spectrum from large to smaller (ℓ ∼ 200) scales, consistent with that ex- pected from acoustic oscillations in the early Universe. We compare this Python V map to a map made from data taken in the third year of Python. Python III observations were made at a frequency of 90 GHz and covered a subset of the region of the sky covered by Python V observations, which were made at 40 GHz. Good agreement is obtained both visually (with a ﬁltered version of the map) and via a likelihood ratio test.
Cosmological Constant and Quintessence from a Correlation Function Comoving Fine Feature in the 2dF Quasar Redshift Survey
(2001-06-05) Roukema, B. F.; Mamon, G. A.
Local maxima at characteristic comoving scales have previously been claimed to exist in the density perturbation spectrum at the wavenumber k = 2π/LLSS, where LLSS ∼ 100–200 h−1 Mpc (comoving), at low redshift (z < ∼0.4) for several classes of tracer objects, at z ≈ 2 among quasars, and at z ≈ 3 among Lyman break galaxies. Here, this cosmic standard ruler is sought in the “10K” initial release of the 2dF QSO Redshift Survey (2QZ-10K), by estimating the spatial two-point autocorrelation functions ξ(r) of the three-dimensional (comoving, spatial) distribution of the N = 2378 quasars in the most completely observed and “covered” sky regions of the catalogue, over the redshift ranges 0.6 < z < 1.1 (“low-z”), 1.1 < z < 1.6 (“med-z”) and 1.6 < z < 2.2 (“hi-z”). Because of the selection method of the survey and sparsity of the data, the analysis was done conservatively to avoid non-cosmological artefacts. (i) Avoiding a priori estimates of the length scales of features, local maxima in ξ(r) are found in all three diﬀerent redshift ranges. The requirement that a local maximum be present in all three redshift ranges at a ﬁxed comoving length scale implies strong, purely geometric constraints on the local cosmological parameters, in which case the length scale of the local maximum common to the three redshift ranges is 2LLSS = 244±17 h−1 Mpc. (ii) For a standard cosmological constant FLRW model, the matter density and cosmological constant are constrained to Ωm = 0.25 ± 0.10, ΩΛ = 0.65±0.25 (68% conﬁdence), Ωm = 0.25±0.15, ΩΛ = 0.60±0.35 (95% conﬁdence), respectively, from the 2QZ-10K alone. Independently of the type Ia supernovae data, the zero cosmological constant model (ΩΛ = 0) is rejected at the 99.7% conﬁdence level. (iii) For an eﬀective quintessence (wQ) model and zero curvature, wQ < −0.5 (68% conﬁdence), wQ < −0.35 (95% conﬁdence) are found, again from the 2QZ-10K alone. In a diﬀerent analysis of a larger (but less complete) subset of the same 2QZ-10K catalogue, Hoyle et al. (2001) found a local maximum in the power spectrum to exist for widely diﬀering choices of Ωm and ΩΛ, which is diﬃcult to understand for a genuine large scale feature at ﬁxed comoving length scale. A resolution of this problem and deﬁnitive results should come from the full 2QZ, which should clearly provide even more impressive constraints on ﬁne features in density perturbation statistics, and on the local cosmological parameters Ωm, ΩΛ and wQ
Data analysis of continuous gravitational wave : All sky search and study of templates
(2001-07-01) Srivastava, D. C.; Sahay, S. K.
We have studied the problem of all sky search in reference to continuous gravita- tional wave particularly for such sources whose wave-form are known in advance. We have made an analysis of the number of templates required for matched ﬁlter analysis as applicable to these sources. We have employed the concept of ﬁtting factor (FF); treating the source location as the parameters of the signal manifold and have studied the matching of the signal with templates corresponding to different source locations. We have investigated the variation of FF with source location and have noticed a sym- metry in template parameters, θT and φT . It has been found that the two different template values in source location, each in θT and φT , have same FF. We have also computed the number of templates required assuming the noise power spectral density Sn(f) to be ﬂat. It is observed that higher FF requires exponentially increasing large number of templates.
Data analysis of continuous gravitational wave : Fourier transform - I
(2001-03-12) Srivastava, D. C.; Sahay, S. K.
We present the Fourier Transform of a continuous gravitational wave. We have analysed the data set for one day observation time and our analysis is applicable for arbitrary location of detector and source. We have taken into account the effects arising due to rotational as well as orbital motions of the earth.
Data analysis of continuous gravitational wave: Fourier transform-II
(2001-06-02) Srivastava, D. C.; Sahay, S. K.
In this paper we obtain the Fourier Transform of a continuous gravitational wave. We have analysed the data set for (i) one year observation time and (ii) arbitrary obser- vation time, for arbitrary location of detector and source taking into account the effects arising due to rotational as well as orbital motion of the earth. As an application of the transform we considered spin down and N-component signal analysis.
Detection of rotational lines of NaSH molecule
(2001-07-02) Sharma, A. K.; Chandra, Suresh
Diamagnetic screening of the magnetic field in accreting neutron stars
(2001-09-20) Choudhuri, Arnab Rai; Konar, Sushan
A possible mechanism for screening of the surface magnetic ﬁeld of an accreting neutron star, by the accreted material, is investigated. In particular, we investigate the nature of the evolution of the internal ﬁeld conﬁguration in the case of a) a polar cap accretion and b) a spherical accretion