2004 (IPP)
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Item Suggestions for an interstellar C7H2 Search(2011-07-06) Chandra, Suresh; Musrif, P. G.; Dharmkare, Ram M.Laboratory detection of the ring-chain molecule c-C7H2 has been reported by McCarthy et al. [McCarthy, M.C., Travers, M.J., Gottlieb, C.A., Thaddeus, P., 1997. A&A 483, L139]. Two ring-chain molecules c-C3H2 and c-C5H2 of this series have already been detected in the cosmic objects. We suggest that the c-C7H2 may be identified in cool cosmic objects through its transitions 414–505,515–606,616–707 and 717–808 at 23.241, 21.105, 18.953 and 16.787 GHz, respectively, in absorption against the CMB. Since, in absence of the availability of collisional rates, we have used scaled values for them, we have checked the sensitivity of the results on the collisional rates, by enhancing the rates for the transitions with Dka = 0 by a factor of 10. Though the transitions are not found sensitive to the collisional rates, our results still may be treated as qualitative in nature. These absorption lines may play an important role for identification of c-C H in cool cosmic objects.Item What is needed of a tachyon if it is to be the dark energy?(2011-07-06) Copeland, E. J.; Garousi, M. R.; Sami, M.; et al.We study a dark energy scenario in the presence of a tachyon field φ with potential V (φ) and a barotropic perfect fluid. The cosmological dynamics crucially depends on the asymptotic behavior of the quantity λ = −MpVφ/V 3/2 . If λ is a constant, which corresponds to an inverse square potential V (φ) ∝ φ−2 , there exists one stable critical point that gives an acceleration of the universe at late times. When λ → 0 asymptotically, we can have a viable dark energy scenario in which the system approaches an “instantaneous” critical point that dynamically changes with λ. If |λ| approaches infinity asymptotically, the universe does not exhibit an acceleration at late times. In this case, however, we find an interesting possibility that a transient acceleration occurs in a regime where |λ| is smaller than of order unity.Item Unifying Brane World Inflation with Quintessence(2011-07-06) Sami, M.; Dadhich, NareshWe review the recent attempts of unifying inflation with quintessence. It appears natural to join the two ends in the framework of brane world cosmology. The models of quintessential inflation belong to the class of non-oscillatory models for which the mechanism of conventional reheating does not work. Reheating through gravitational particle production is inefficient and leads to the excessive production of relic gravity waves which results in the violation of nucleosynthesis constraint. The mechanism of instant preheating is quite efficient and is suitable for brane world quintessential inflation. The model is shown to be free from the problem of excessive production of gravity waves. The prospects of Gauss-Bonnet brane world inflation are also briefly indicated.Item Unified approach to scaling solutions in a general cosmological background(2011-07-06) Tsujikawa, Shinji; Sami, M.Our ignorance about the source of cosmic acceleration has stimulated study of a wide range of models and modifications to gravity. Cosmological scaling solutions in any of these theories are privileged because they represent natural backgrounds relevant to dark energy. We study scaling solutions in a generalized background H2 ∝ ρn T in the presence of a scalar field ϕ and a barotropic perfect fluid, where H is a Hubble rate and ρT is a total energy density. The condition for the existence of scaling solutions restricts the form of Lagrangian to be p = X1/ng(Xenλϕ), where X = −gµν ∂µϕ∂νϕ/2 and g is an arbitrary function. This is very useful to find out scaling solutions and corresponding scalar-field potentials in a broad class of dark energy models including (coupled)- quintessence, ghost-type scalar field, tachyon and k-essence. We analytically derive the scalar-field equation of state wϕ and the fractional density Ωϕ and apply it to a number of dark energy models.Item U BV RI CCD photometric study of the open clusters basel 4 and NGC 7067(2011-07-06) Yadav, R. K. S.; Sagar, RamIn this paper we present UBV RI CCD photometry in the region of two young open star clusters Basel 4 and NGC 7067 for the first time. Our sample consists of ∼ 4000 stars down to V ∼ 21 mag. Stellar surface density profile indicates that radius of Basel 4 and NGC 7067 are about 1.8 and 3.0 arcmin respectively. The (U −B) versus (B − V ) diagrams indicate that metallicity of NGC 7067 is solar while that of Basel 4 is Z ∼ 0.008. We estimate the mean value of E(B −V ) = 0.45±0.05 and 0.75±0.05 mag for Basel 4 and NGC 7067 respectively. The analysis of 2MASS JHK data in combination with the optical data in both the clusters yields E(J − K) = 0.30±0.20 mag and E(V − K) = 1.60±0.20 mag for Basel 4 while E(J − K) = 0.40±0.20 mag and E(V −K) = 2.10±0.20 mag for NGC 7067. Furthermore, colour excess diagrams show a normal interstellar extinction law towards both the clusters. Using the intrinsic colour-magnitude diagrams of the cluster members, we esti- mated the distances of the clusters as 3.0±0.2 and 3.6±0.2 Kpc for Basel 4 and NGC 7067 respectively. By fitting the proper metallicity isochrones to the bright cluster members we estimated the age of the clusters as 200±50 and 100±25 Myr for Basel 4 and NGC 7067 respectively. The mass function slope which is derived by applying the corrections of field star contamination and data incompleteness are 1.55 ± 0.25 and 1.68 ± 0.47 for Basel 4 and NGC 7067 respectively. The values of mass function slopes are thus not too different from the Salpeter’s (1955) value. Mass segregation is observed in both the clusters which may be due to the dynamical evolutions or imprint of star formation processes or boItem Tracking pulsar dispersion measures using the GMRT(2011-07-06) Ahuja, A. L.; Gupta, Y.; Mitra, D.; et al.Item Time dependence of the proton-to-electron mass ratio(2011-07-06) Petitjean, Patrick; Ivanchik, A.; Srianand, R.; et al.We have measured with high precision the position of 79 molecular hydrogen absorption lines of Lyman and Werner bands from two absorption systems at zabs = 2.594733 and 3.024899, in the spectra of quasars Q 0405–443 and Q 0347–383, respectively, in order to constrain the cosmological variation of the proton-to-electron mass ratio, µ = mp/me.Dataareof the highest spectral resolution (R = 53 000) and signal to noise ratio (S/N = 30–70) for such quasars. The absorption lines are not saturated and their profiles can be modelled as simple Gaussian functions. We find a correlation between the observed redshift of the lines and the sensitivity of the line positions to a change in µ. This can be interpreted as a variation of µ with µ/µ = (2.97 ± 0.74) × 10−5 over the past ∼12 Gyrs. As this result is based on two systems one cannot rule out that unknown systematics could cause a false-alarm detection. Thus the result needs to be confirmed with additional data. It is also very important to improve the accuracy of the laboratory wavelengths as the significance of our result depends on the accuracy to which they are known.Item Time-Delay Interferometry(2011-07-06) 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 Spherical and non-spherical gravitational collapse in Hussain spacetime(2011-06-06) Patil, K. D.; Thool, U. S.We investigate the nature of singularities arising in Husain solution. We analyze both spherical and non-spherical gravitational collapse in Husain spacetime. An interesting feature that emerges is that gravitational collapse of spherical cosmological Husain solution lead to the formation of naked singularities, while non-spherical cosmological collapse proceeds to form a black hole. Further strength of naked singularities arising in these spacetimes has been analyzed. It is found that these naked singularities are strong in Tipler’s sense.Item Suggesions for an interstellar C5H2 search(2011-07-06) Chandra, Suresh; Shinde, S. A.Laboratory detection of four isomers of C5H2 molecule have been reported by Travers et al. (1997), McCarthy et al. (1997), and Gottlieb et al. (1998). They suggested for detection of the ring-chain isomer of C5H2 (c-C5H2)incosmic objects, as it is the most stable one in comparison to the others. Two transitions 313−212 and 303−202 at 19.147 GHz and 19.606 GHz, respectively, of c-C5H2 have been detected in TMC-1. We suggest that the c-C5H2 may be identified in cool cosmic objects through its transition 313−404 at 4.3 GHz in absorption against the cosmic microwave background. Since in absence of availability of the collisional rates, we have used scaled values for them, we have checked the sensitivity of the lines on the rates by enhancing the rate for the transitions with ∆ka = 0 by a factor of 10. Though the transitions are not found sensitive, our results may be treated as qualitative in nature. This absorption line may play an important role for identification of c-C5H2 in cosmic objects.