2004 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/625

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End date: 2012Subject: search.filters.subject.Cosmology

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    Nonsingular spherical models with a variable cosmological term
    (2011-07-06) Pradhan, Anirudh; Srivastava, Kashika; Lal, Amrit
    Exact solutions of the Einstein’s field equations describing a spheri- cally symmetric cosmological model without a big bang or any other kind of singularity recently obtained by Dadhich and Patel (2000) are revis- ited. The matter content of the model is a shear-free perfect fluid with isotropic pressure and a radial heat flux. Three different exact solutions are obtained for both perfect fluid and fluid with bulk viscosity. It turns out that the cosmological rerm Λ(t) is a decreasing function of time, which is consistent with recent observations of type Ia supernovae.
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    Generation of electromagnetic fields in string cosmology with a massive scalar field on the anti D-brane
    (2012-07-06) Garousi, M. R.; Sami, M.; Tsujikawa, Shinji
    We study the generation of electromagnetic fields in a string-inspired scenario associated with a rolling massive scalar field φ on the anti-D3 branes of KKLT de Sitter vacua. The 4-dimensional DBI type effective action naturally gives rise to the coupling between the gauge fields and the inflaton φ, which leads to the production of cosmological magnetic fields during inflation due to the breaking of conformal invariance. We find that the amplitude of magnetic fields at decoupling epoch can be larger than the limiting seed value required for the galactic dynamo. We also discuss the mechanism of reheating in our scenario and show that gauge fields are sufficiently enhanced for the modes deep inside the Hubble radius with an energy density greater than that of the inflaton.
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    Cylindrically symmetric inhomogeneous cosmological models with viscous fluid & varying /\>
    (2012-07-06) Pradhan, A.; Singh, P. K.; Jotania, Kanti
    Cylindrically symmetric non-static cosmological models representing a bulk viscous fluid distribution have been obtained which are inhomogeneous and anisotropic. Without assuming any adhoc law, we obtain a cosmological constant as a decreasing function of time. Various physical and geometrical features of the models are also discussed.
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    Current status of observational cosmology
    (2011-07-06) Ostriker, Jeremiah P.; Souradeep, Tarun
    Observational cosmology has indeed made very rapid progress in recent years. The ability to quantify the universe has largely improved due to observational constraints coming from structure formation. The transition to precision cosmology has been spear- headed by measurements of the anisotropy in the cosmic microwave background (CMB) over the past decade. Observations of the large scale structure in the distribution of galax- ies, high red-shift supernova, have provided the required complementary information. We review the current status of cosmological parameter estimates from joint analysis of CMB anisotropy and large scale structure (LSS) data. We also sound a note of caution on overstating the successes achieved thus far.
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    Cosmology from rolling massive scalar field on the anti-D3 Brane of de Sitter Vacua
    (2012-07-06) Garousi, M. R.; Sami, M.; Tsujikawa, Shinji
    We investigate a string-inspired scenario associated with a rolling massive scalar field on D-branes and discuss its cosmological implications. In particular, we discuss cosmological evolution of the massive scalar field on the ant-D3 brane of KKLT vacua. Unlike the case of tachyon field, because of the warp factor of the anti-D3 brane, it is possible to obtain the required level of the amplitude of density perturbations. We study the spectra of scalar and tensor perturbations generated during the rolling scalar inflation and show that our scenario satisfies the observational constraint coming from the Cosmic Microwave Background anisotropies and other observational data. We also implement the negative cosmological constant arising from the stabilization of the modulus fields in the KKLT vacua and find that this leads to a successful reheating in which the energy density of the scalar field effectively scales as a pressureless dust. The present dark energy can be also explained in our scenario provided that the potential energy of the massive rolling scalar does not exactly cancel with the amplitude of the negative cosmological constant at the potential minimum.