AR-2019-2020

work has been done in collaboration with Abdus Sattar. Hemwati Nandan Analytic solutions of the geodesic equation for Reissner-Nordstrm-(anti-)de Sitter black holes sur- rounded by different kinds of regular and exotic matter fields The purpose of this study is the derivation of the equation of motion for particles in the spacetime of Reissner-Nordstrm-(anti-)de Sitter black holes in the background of different kinds of regular and exotic matter fields. The complete analytical solu- tions of the geodesic equations are given in terms of the elliptic Weierstra β - ℘ function and the hyperel- liptic Kleinian σ -function. Finally, after analyzing the geodesic motion of test particles and light us- ing parametric diagrams and effective potentials, we present a list of all possible orbits. This work has been done in collaboration with Arindam Ku- mar Chatterjee, Kai Flathmann, and Anik Rudra. Long-term (2005-2012) measurements of near- surface air pollutants at an urban location in the Indo-Gangetic Basin Simultaneous long-term measurements of near- surface air pollutants at an urban station, New Delhi, were studied during 2005 − 2012 to un- derstand their distribution on different temporal scales. The annual mean mass concentrations of Nitrogen dioxide ( NO 2 ), Sulphur dioxide ( SO 2 ), particulate matter less than 10 μm ( PM 10 ) and sus- pended particulate matter (SPM) were found to be 62 . 0 ± 27 . 6 , 12 . 5 ± 8 . 2 , 253 . 7 ± 134 and 529 . 2 ± 213 . 1 μg/m 3 , respectively. The 24 − hr mean mass concentrations of NO 2 , PM 10 and SPM were ex- ceeded on ∼ 27% , 87% and 99% days that of to- tal available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for SO 2 , which could be attributed to reduction of Sulphur in diesel, use of cleaner fuels such as compressed nat- ural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of NO 2 , PM 10 and SPM showed an increasing trend, while SO 2 appears to be decreasing since 2008. Air mass cluster analysis showed that north-northwest trajectories accounted for the highest mass concen- trations of air pollutants (more prominent in the winter/post-monsoon season); however, the low- est were associated with the southeast trajectory cluster. This work has been done in collaboration with Nanda Kishore, Atul K. Srivastava, Chhavi P. Pandey, S Agrawal, Narendra Singh et al. Biswajit Pandey Can we constrain the dark energy equation of state parameters using conguration entropy ? We propose a new scheme for constraining the dark energy equation of state parameter/parameters based on the study of evolution of conguration en- tropy. We analyze a set of one parameter and two parameters dynamical dark energy models and find that the derivative of the configuration entropy in all the dynamical dark energy models, exhibit a minimum. The magnitude of the minimum of the entropy rate is decided by both the parametriza- tion of the equation of state as well as the as- sociated parameters. The location of the mini- mum of the entropy rate is less sensitive to the form of the parametrization but depends on the associated parameters. We determine the best fit equations for the location and magnitude of the minimum of the entropy rate in terms of the pa- rameter/parameters of the dark energy equation of state. These relations would allow us to con- strain the dark energy equation of state parame- ter/parameters for any given parametrization pro- vided the evolution of the configuration entropy in the Universe is known from observations. This work has been done in collaboration with Biswajit Das. Unravelling the cosmic web: An analysis of the SDSS DR14 with the local dimension We analyse a volume-limited galaxy sample from the Sloan Digital Sky Survey (SDSS) in order to study the environments of galaxies on different length-scales in the local universe. We measure the local dimension of the SDSS galaxies on differ- ent length-scales and we find that sheets or sheet- like structures are the most prevalent pattern in the cosmic web throughout the entire range of length-scales. The abundance of sheets peaks at 30h1Mpc and they can extend up to a length-scale of 90h1Mpc. Analysing mock catalogues, we find that the sheets are non-existent beyond 30h1Mpc in