IUCAA Preprints
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Item Cosmological parameter estimation with free-form primordial power spectrum(IUCAA, 2015-02) Hazra, Dhiraj Kumar; Shafieloo, Arman; Tarun, SauradeepItem From Nonparametric Power Spectra to Inference About Cosmological Parameters: A Random Walk in the Cosmological Parameter Space(IUCAA, 2015-02) Aghamousa, Amir; Arjunwadkar, Mihir; Tarun, SauradeepItem Revised cosmological parameters after BICEP 2 and BOSS(IUCAA, 2015-02) Das, Santanu; Mukherjee, Suvodip; Tarun, SauradeepItem SCOPE: An e cient method of Cosmological Parameter Estimation(IUCAA, 2015-02) Das, Santanu; Souradeep, TarunItem Nonlinear sigma model for inflation scenarios.II(2015-01-17) Chervon, S.V.In this paper the self –gravitating nonlinear sigma model is considered in the context of inflation scenarios as an alternative to the self-interacting scalar field theory. The complete set of new exact solutions for the two-component sigma model in the frame work of spatially flat friendmann- Robertson- Walker and de sitter universes is obtained.Item Constraints on omegaB, omega M, and h from MAXIMA and BOOMERANG(2000-10-24) Padmanabhan, T.; Sethi, Shiv K.We analyse the BOOMERANG and MAXIMA results in the context of models with ΩTotal = 1 and ns = 1. We attempt to constrain three other parameters—h, ΩB, and Ωm—from these observations. We show that: (a) the value of ΩBh2 is too high to be compatible with primordial nucleosynthesis observations at 95% confidence level (b) universe with age greater than 12Gyr is ruled out at 95% confidence level and (c) the value of Ωmh is too high to be compatible with the shape of the power spectrum of gravitational clustering. In effect, our analysis shows that models with ΩTotal = 1 and n = 1 are ruled out by BOOMERANG and MAXIMA observations.Item Exploring the expanding universe and dark energy using the statefinder diagnostic(2011-07-05) Ujjaini, Alam; Sahni, Varun; Saini, Tarun Deep; et al.The coming few years are likely to witness a dramatic increase in high quality Sn data as current surveys add more high redshift supernovae to their inventory and as newer and deeper supernova experiments become operational. Given the current variety in dark energy models and the expected improvement in observational data, an accurate and versatile diagnostic of dark energy is the need of the hour. This paper examines the Statefinder diagnostic in the light of the proposed SNAP satellite which is expected to observe about 2000 supernovae per year. We show that the Statefinder is versatile enough to differentiate between dark energy models as varied as the cosmological constant on the one hand, and quintessence, the Chaplygin gas and braneworld models, on the other. Using SNAP data, the Statefinder can distinguish a cosmological constant (w = −1) from quintessence models with w > −0.9 and Chaplygin gas models with κ 6 15 at the 3σ level if the value of Ωm is known exactly. The Statefinder gives reasonable results even when the value of Ωm is known to only ∼ 20% accuracy. In this case, marginalizing over Ωm and assuming a fiducial LCDM model allows us to rule out quintessence with w > −0.85 and the Chaplygin gas with κ 6 7 (both at 3σ). These constraints can be made even tighter if we use the Statefinders in conjunction with the deceleration parameter. The Statefinder is very sensitive to the total pressure exerted by all forms of matter and radiation in the universe. It can therefore differentiate between dark energy models at moderately high redshifts of z < 10.Item Smoothing supernova data to reconstruct the expansion history of the universe(2006-01-10) Shafieloo, Arman; Alam, Ujjaini; Sahni, VarunWe propose a non-parametric method of smoothing supernova data over redshift using a Gaussian kernel in order to reconstruct important cosmological quantities including H(z) and w(z) in a model independent manner. This method is shown to be successful in discriminating between different models of dark energy when the quality of data is commensurate with that expected from the future SuperNova Acceleration Probe (SNAP). We find that the Hubble parameter is especially well-determined and useful for this purpose. The look back time of the universe may also be determined to a very high degree of accuracy ( < ∼ 0.2%) in this method. By refining the method, it is also possible to obtain reasonable bounds on the equation of state of dark energy. We explore a new diagnostic of dark energy– the ‘w-probe’– which can be calculated from the first derivative of the data. We find that this diagnostic is reconstructed extremely accurately for different reconstruction methods even if Ω0m is marginalized over. The w-probe can be used to successfully distinguish between ΛCDM and other models of dark energy to a high degree of accuracy.Item Kaluza-Klein Type Robertson Walker Cosmological Model With Dynamical Cosmological Term Lambda(2005-12-01) Pradhan, Anirudh; Khadekar, G. S.; Patki, VrishaliIn this paper we have analyzed the Kaluza-Klein type RobertsonWalker (RW) cosmological models by considering three different forms of variable Λ: Λ ∼˙ a a 2 , Λ ∼ ¨ a a and Λ ∼ ρ. It is found that, the connecting free parameters of the models with cosmic matter and vacuum energy density parameters are equivalent, in the context of higher dimensional space time. The expression for the look back time, luminosity distance and angular diameter distance are also derived. This work has thus generalized to higher dimensions the well-known results in four dimensional space time. It is found that there may be significant difference in principle at least, from the analogous situation in four dimensional space time.