1. Deepak Jain

    Deen Dayal Upadhyaya College, New Delhi

    Model independent constraints on cosmic curvature

    We use two model-independent methods to constrain the curvature of the universe. In the first method, we study the evolution of the curvature parameter (Ω0k) with redshift by using the observations of the Hubble parameter and transverse comoving distances obtained from the age of galaxies. Secondly, we also use an indirect method based on the mean image separation statistics of gravitationally lensed quasars. The basis of this methodology is that the average image separation of lensed images will show a positive, negative or zero correlation with the source redshift in a closed, open or flat universe respectively. In order to smoothen the datasets used in both the methods, we use a non-parametric method namely, Gaussian Process (GP). Finally from first method we obtain Ω0k=0.025±0.57 for a presumed flat universe while the cosmic curvature remains constant throughout the redshift region 0

  3. Mayukh Raj Gangopadhyay

    Saha Institute Of Nuclear Physics, Kolkata

    A Study in non-canonical domain of Goldstone inflaton

    Inflationary paradigm offers a very attractive solution to resolve the hot big bang cosmology puzzles. One of the problems of the standard inflationary models is most of the textbook models are ruled out or disfavoured by the Planck observations. Another theoretical discomfort about many a models of inflation is related to the super-Planckian field excursion of the inflaton field. In early 90's one elegant solution was proposed by Freese et. al. from the idea of symmetry breaking to produce the inflation potential where the inflaton is a Goldstone boson. Due to the shift symmetry property embedded through the symmetry breaking, the flatness of the potential is maintained which is essential for the model building of inflation. But after recent observations from Planck, natural inflation model is almost ruled out in the standard Λ CDM model. Natural inflation is one class of a general form of inflation known as Goldstone inflation. To have a successful Goldstone inflation, all scales related to the theory has to be sub-Planckian thus keeping the inflaton guarded against the UV correction from the quantum gravity effects. In this work, we have shown that Goldstone inflation in case of a non-canonical dynamical realisation, can have symmetry breaking scales less than the Planck scale and can have observational predictions in perfect agreement with the latest data. Thus, a non-canonical realisation of generalised Goldstone inflation can be one of the prime candidates to explain the inflationary dynamics.

  5. Sandeep Kumar Kataria

    IIA, Bangalore

    A study of Isolated halos distribution in Large-scale structures of universe

    In this study we have explored the mass spectrum of isolated halos along with their local densities from high redshift z~ 12 to present universe z~0. For conducting this study we have used Horizon Run 4 (Kim & Changbom et al 2015) data products. Horizon Run 4 is N-body simulation designed to study evolutions of galaxies and large-scale structures of the Universe. In this simulation halo mass resolution scale down to M s = 2.7 × 10^{11} h^{-1} M sun; which is better for isolated halo study. We have found that isolated halos shows maximum in their probability distribution for over density regions which corresponds to values ranging from 0.1 to 1 at z~0. Apart from this non-isolated halos shows maximum in their probability distribution for over density regions which varies from 1 to 10. We have also shown that masses for which isolated galaxies shows maximum probability distribution is more than non-isolated ones at z~0. This implies that most of the satellites of progenitors of isolated halos have merged into progenitors during their evolution. Further study includes merger tree history of these isolated halos

  7. Bikash Chandra Paul

    North Bengal University, Siliguri

    Emergent Universe with interacting fluids

    Emergent Universe is studied in modified gravity. It has no bigbang singularity. To understand evaluation of the universe it is necessary to have a static Einstein universe in the infinitely past and in course of time the present universe will emerge from the state. A non-linear equation of state is required here, which is essentially describes a composition of three fluids. It is shown that interacting fluid gives a physically realistic solution to describe the present universe.

  9. Priyank Parashari

    PRL, Ahmedabad

    Viscosity as a solution to σ8 tension and it's effect on neutrino mass

    It has been reported that there are some discordances between cosmic microwave background (CMB) and large scale structure (LSS) surveys. In particular, the value of \sigma 8, the r.m.s. fluctuation of density perturbations at 8 h^-1Mpc scale and H0, the value of Hubble parameter observed today, inferred from CMB and LSS observations, are not in agreement with each other. Moreover, these discordances can be resolved by using effective viscous description of cold dark matter (CDM) on large scales. Effective field theory of dark matter fluid on large scales predicts the presence of viscosity of the order of 10^-6 H0 M P^2. The same order of viscosity have also been found to resolve the discordance between LSS observations and Planck CMB data. Since massive neutrinos suppresses the matter power spectrum on the small length scales similar to the viscosity, we, therefore, use the viscous dark matter description to study the neutrinos and demonstrate that one can indeed constrain the masses of the neutrinos in a stringent way. We found the bounds on sum of neutrino masses to be \sum m \nu < 0.266 eV for normal hierarchy and \sum m \nu < 0.146 eV for inverted hierarchy.