AR-2019-2020

measured, galactic structures are supposed to be formed out of dark matter clustering. Some ex- amples of supermassive black holes in the central regions of high redshift galaxies say that the con- cerned supermassive black holes have completed their constructions in a time less than it gener- ally should be. To justify such discrepancies, we are forced to model about existences of black hole mimickers and exotic phenomena acting near the supermassive black holes. Motivated by these, we study the natures of exotic matters, especially dark energy near the black holes. We choose modified Chaplygin gas as dark energy candidate. Again, the descriptions of gravitational waves or the atten- uations of them when they are tunnelling through cosmological distances help us to measure the shear viscosity of the medium through which the waves have been travelled. Delayed decaying models of dark matters also suggest that dark energy and vis- cosity may come up as a byproduct of such decays or interactions. We consider the viscous nature of the medium, i.e., the dark energy. To do so, we choose an alpha-disc model as proposed by Shakura and Sunyaev. We study the variations of densities through accretion and wind branches for a differ- ent amount of viscosity regulated by the Shakura- Sunyaev alpha parameter, spin parameter and dif- ferent properties of accreting fluids, viz, the proper- ties of adiabatic fluid and modified Chaplygin gas. We compare these results with each other and some existing density profiles drawn from observational data-based simulations. We follow that the result supports the data observed till date. Specifically, we see the wind to get stronger for dark energy as accreting agent. Besides, we see the accretion to have a threshold drop if the viscosity is chosen along with the repulsive effects of dark energy. This work has been done in collaboration with Sandip Dutta. Subenoy Chakraborty Quantum cosmology for non-minimally coupled scalar field in FLRW spacetime : A symmetry anal- ysis The present work deals with quantum cosmology for non-minimally coupled scalar field in the back- ground of FLRW spacetime model. The Wheeler- DeWitt equation is constructed and symmetry analysis is carried out. The Lie point symmetries are related to the conformal algebra of the min- isuperspace while solution of the Wheeler-DeWitt equation is obtained using conserved currents of the Noether symmetries. This work has been done in collaboration with Sourav Dutta, and Muthusamy Lakshmanan. Homogeneous and isotropic spacetime, modified torsion field and complete cosmic scenario This work deals with cosmological solutions de- scribing different phases of the Universe for the homogeneous and isotropic FLRW model with tor- sion. Normally, torsion field is not suitable for max- imally symmetric spacetime model. However, one may use a specific profile of vectorial torsion field, derived from a scalar function. By proper choices of the torsion scalar function, it is shown that a con- tinuous cosmic evolution starting from the emer- gent scenario to the present late time acceleration is possible. Also thermodynamics of the system is analyzed and equivalence with Einstein gravity is discussed. This work has been done in collabora- tion with Akash Bose. Nand Kumar Chakradhari Optical and UV studies of type Ia supernovae SN 2009ig and SN 2012cg We present an extensive optical-ultraviolet pho- tometry, and analysis of a series of optical spectra of type Ia supernovae SN 2009ig and SN 2012cg. The observations range from − 15 to +185 d for SN 2009ig and − 14 to 316 d for SN 2012cg, with respect to maximum light in B band. Both SN 2009ig, and SN 2012cg exhibit similar proper- ties. They have similar decline rate parameter (Δ m 15 ( B ) true = 0.92 ± 0.04 for SN 2009ig and 0.93 ± 0.06 for SN 2012cg) and B band peak absolute magnitude ( − 19.45 ± 0.40 mag for SN 2009ig and − 19.50 ± 0.31 mag for SN 2012cg). Their early spectra show high velocity features in Si ii and Ca ii lines. The strong Fe iii , Si iii and weak Si ii λ 5972 line during pre-maximum phase are indicative of hot photosphere. The post-maximum velocity evo- lution shows a plateau like phase with velocities ∼ 13,000 km s − 1 for SN 2009ig and ∼ 10,000 km s − 1 for SN 2012cg. Both events show spectral evolution similar to normal SNe Ia and fall in LVG and Core Normal subgroup. Both have smaller strength ra- tio ( R (Si ii ) = 0.17 for SN 2009ig, and 0.20 for SN 2012cg) consistent with smaller Δ m 15 ( B ). Peak bolometric luminosities (log L max bol ) of these events