2001 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/628

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    Inflation with oscillations
    (2001-02-02) Sami, M.
    In this paper we investigate the general features of ”Oscillatory Inflation”. In adiabatic approxi- mation , we derive a general formula for the number of e-foldings ˜ N which reduces to the standard expression in case of the slow role approximation and leads to the Damour-Mukhanov type expres- sion for the slowly varying adiabatic index. We apply our result to the logarithmic potential and arrive at a simple and elegant formula for the number of e-foldings.We evolve the field equations numerically and observe a remarkable agreement with the analytical result.
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    How to distinguish a nearly flat Universe from a flat Universe using the orientation independence of a comoving standard ruler
    (2001-01-20) Roukema, B. F.
    Several recent observations using standard rulers and standard candles now suggest, either individually or in combination, that the Universe is close to flat, i.e. that the curvature radius is about as large as the horizon radius (∼ 10h−1 Gpc) or larger. Here, a method of distinguishing an almost flat universe from a precisely flat universe using a single observational data set, without using any microwave background information, is presented. The method (i) assumes that a standard ruler should have no preferred orientation (radial versus tangential) to the observer, and (ii) requires that the (comoving) length of the standard ruler be known independently (e.g. from low redshift estimates). The claimed feature at fixed comoving length in the power spectrum of density perturbations, detected among quasars, Lyman break galaxies or other high redshift objects, would provide an adequate standard candle to prove that the Universe is curved, if indeed it is curved. For example, a combined intrinsic and measurement uncertainty of 1% in the length of the standard ruler L applied at a redshift of z = 3 would distinguish an hyperbolic (Ωm = 0.2,ΩΛ = 0.7) or a spherical (Ωm = 0.4, ΩΛ = 0.7) universe from a flat one to 1 − P > 95% confidence
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    How to avoid the ambiguity in applying the copernican principle for cosmic topology : Take the observational approach
    (2001-03-01) Roukema, B. F.
    It is often stated that homogeneity and isotropy of the Universe are assumptions of the almost Friedmann- Lemaˆıtre (FL) model (the hot big bang model), inspired from the Copernican Principle. However, only local homogeneity and isotropy are required by the model: multiply connected almost FL models are locally homogeneous and isotropic, but they can be globally anisotropic and/or globally inhomogeneous. Toy models are used here to show how global anisotropy and/or global inhomogeneity of an almost FL model could be shown directly in observations. This approach may avoid having to make any assumptions regarding global anisotropy and inhomogeneity.
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    Non-conformally flat bulk spacetime and the 3-brane world
    (2001-01-05) Singh, Parampreet; Dadhich, Naresh
    We show that for non-conformally flat bulk spacetime, there exist no bound modes for zero mass graviton on the 3-brane. The brane world model is therefore unstable for the bulk spacetime being different from the conformally flat anti - de Sitter space.
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    New stationary vacuum solution dual to the kerr solution
    (2001-05-01) Turakulov, Z . Ya.; Dadhich, Naresh
    We present a stationary axially symmetric two parameter vacuum solution which could be considered as “dual” to the Kerr solution. It is obtained by removing the mass parameter from the function of the radial coordinate and introducing a dimensionless parameter in the function of the angle coordinate in the metric functions. It turns out that it is in fact the massless limit of the Kerr - NUT solution.
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    R=O spacetimes and self-dual lorentzian wormholes
    (2001-04-02) Dadhich, Naresh; Kar, Sayan; Mukherjee, Sailajananda; et al.
    A two–parameter family of spherically symmetric, static Lorentzian wormholes is obtained as the general solution of the equation ρ = ρt = 0, where ρ = Tij ui uj , ρt = (Tij − 1 2T gij ) ui uj , and ui ui = −1. This equation characterizes a class of spacetimes which are “self dual” (in the sense of electrogravity duality). The class includes the Schwarzschild black hole, a family of naked singularities, and a disjoint family of Lorentzian wormholes, all of which have vanishing scalar curvature (R = 0). Properties of these spacetimes are discussed. Using isotropic coordinates we delineate clearly the domains of parameter space for which wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be obtained. A model for the required “exotic” stress–energy is discussed, and the notion of traversability for the wormholes is also examined.
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    Relic gravity waves from Braneworld inflation
    (2001-10-02) Sahni, Varun; Sami, M.; Souradeep, Tarun
    We discuss a scenario in which extra dimensional effects allow a scalar field with a steep potential to play the dual role of the inflaton as well as dark energy (quintessence). The post-inflationary evo- lution of the universe in this scenario is generically characterised by a ‘kinetic regime’ during which the kinetic energy of the scalar field greatly exceeds its potential energy resulting in a ‘stiff’ equa- tion of state for scalar field matter Pφ ≃ ρφ. The kinetic regime precedes the radiation dominated epoch and introduces an important new feature into the spectrum of relic gravity waves created quantum mechanically during inflation. The amplitude of the gravity wave spectrum increases with wavenumber for wavelengths shorter than the comoving horizon scale at the commencement of the radiative regime. This ‘blue tilt’ is a generic feature of models with steep potentials and imposes strong constraints on a class of inflationary braneworld models. Prospects for detection of the grav- ity wave background by terrestrial and space-borne gravity wave observatories such as LIGO II and LISA are discussed.
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    Near-solar metallicity damped lyman-alpha system toward the BAL quasar Tol 1037 - 2703
    (2001-02-01) Srianand, R.; Petitjean, Patrick
    We report the detection of a Broad Absorption Line (BAL) outflow in the spectrum of the zem (Mg ii) = 2.201 QSO Tol 1037−2703 with three main BALs at 36000, 25300 and 22300 km s −1 outflow velocities. Although the overall flow is dominated by high ionization lines like N v and C iv , the gas of highest velocity shows absorption from Mg i, Mg ii and Fe ii. Covering factor arguments suggest that the absorbing complexes are physically associated with the QSO and have transverse dimensions smaller than that of the UV continuum emitting region (r < 0.1 pc). We show that the C iv absorption at zabs = 2.082 has a covering factor fc ∼ 0.86 and the absorption profile has varied over the last four years. The detection of absorption from excited fine structure levels of C ii and Si ii in narrow components embedded in the C iv trough reveals large density inhomogeneities. IR pumping is the most likely excitation process. The zabs = 2.139 system is a moderately damped Lyman-α system with log N(H i) ∼ 19.7. The weakness of the metal lines together with the high quality of the data make the metallicity measurements particularly reliable. The absolute metallicity is close to solar with [Zn/H] = −0.26. The α-chain elements have metallicities consistently solar (respectively +0.05, −0.02, −0.03 and −0.15 for [Mg/H], [Si/H], [P/H] and [S/H]) and iron peak elements are depleted by a factor of about two ([Fe/Zn], [Cr/Zn], [Mn/Zn] and [Ni/Zn] are equal to −0.39, −0.27, −0.49, −0.30). Lines from C i are detected but H2 is absent with a molecular to neutral hydrogen fraction less than 8×10−6 . From the ionization state of the gas, we argue that the system is situated ∼few Mpc away from the QSO. High metallicity and low nitrogen abundance, [N/Zn] = −1.40, favor the idea that metals have been released by massive stars during a starburst of less than 0.5 Gyr of age. Using the upper limit on the C i ∗ column density in two components, we obtain upper limits on the background temperature of 16.2 and 13.2 K respectively.
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    Near-infrared [Fe II] emission from supernova remnants and the supernova rate of starburst galaxies
    (2001-02-01) Morel, T.; Doyon, R.; St-Louis, N.
    In an effort to better calibrate the supernova rate of starburst galaxies as deter- mined from near-infrared [Fe II] features, we report on a [Fe II] λ1.644 µm line-imaging survey of a sample of 42 optically-selected supernova remnants (SNRs) in M33. A wide range of [Fe II] luminosities are observed within our sample (from less than 6 to 695 L⊙). Our data suggest that the bright [Fe II] SNRs are entering the radiative phase and that the density of the local interstellar medium (ISM) largely controls the amount of [Fe II] emission. We derive the following relation between the [Fe II] λ1.644 µm line luminosity of radiative SNRs and the electronic density of the postshock gas, ne: L[Fe II] (L⊙) ≈ 1.1 ne (cm−3). We also find a correlation in our data between L[Fe II] and the metallicity of the shock-heated gas, but the physical interpretation of this re- sult remains inconclusive, as our data also show a correlation between the metallicity and ne. The dramatically higher level of [Fe II] emission from SNRs in the central regions of starburst galaxies is most likely due to their dense environments, although metallicity effects might also be important. The typical [Fe II]-emitting lifetime of a SNR in the central regions of starburst galaxies is found to be of the order of 104 yr. On the basis of these results, we provide a new empirical relation allowing the de- termination of the current supernova rate of starburst galaxies from their integrated near-infrared [Fe II] luminosity.
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    Recycling the universe using scalar fields
    (2001-07-02) Kanekar, Nissim; Sahni, Varun; Shtanov, Yuri
    We examine the behaviour of a closed oscillating universe filled with a homogeneous scalar field and find that, contrary to naive expectations, such a universe expands to larger vol- umes during successive expansion epochs. This intriguing be- haviour introduces an arrow of time in a system which is time- reversible. The increase in the maximum size of the universe s closely related to the work done on/by the scalar field dur- ng one complete oscillatory cycle which, in turn, is related to the asymmetry in the scalar field equation of state dur- ng expansion and collapse. Our analysis shows that scalar fields with polynomial potentials V (φ) = λφq , q > 1 lead to a growing oscillation amplitude for the universe: the increase n amplitude between successive oscillations is more signifi- cant for smaller values of q. Such behaviour allows for the effective recycling of the universe. A recycled universe can be quite old and can resolve the flatness problem. These results have strong bearing on cosmological models in which the role of dark matter is played by a scalar field. They are also rele- vant for chaotic inflationary models of the early universe since they demonstrate that, even if the universe fails to inflate the first time around, it will eventually do so during future oscil- atory cycles. Thus, the space of initial conditions favourable or chaotic inflation increases significantly.