AR_final file_2018-19

redshift ( z ∼ 8) Lyman α emitter data and the non- flat models. This is solely due to the fact that the closed models have a relatively higher reionization optical depth compared to the flat one, which in turn demands more high-redshift ionizing sources and favours an extended reionization starting as early as z ≈ 14. We conclude that as opposed to flat-cosmology, for the non-flat cosmology models, (i) the escape fraction needs steep redshift evolu- tion and even unrealistically high values at some redshifts, and (ii) most of the physical parameters require to have non-monotonic redshift evolution, especially apparent when Lyman α emitter data is included in the analysis. This work has been done in collaboration with Tirthankar, R. Choudhaury, and Bharat Ratra. Can SKA Phase 1 go much beyond the LHC in su- persymmetry search? We study the potential of the Square Kilometre Array in the first phase (SKA1) in detecting dark matter annihilation signals from dwarf spheroidals in the form of diffuse radio synchrotron. Taking the minimal supersymmetric standard model as an illustration, we show that it is possible to detect such signals for dark matter masses about an order of magnitude beyond the reach of the Large Hadron Collider, with about 100 hours of observation with the SKA1. This work has been done in collabora- tion with Arpan Kar, Biswarup Maukhopadhyaya, and Tirthankar R. Choudhury. Kamakshya Prasad Modak Two Component Feebly Interacting Massive Parti- cle (FIMP) dark matter We explore the idea of an alternative candidate for particle dark matter, namely Feebly Interact- ing Massive Particle (FIMP) in the framework of a two component singlet scalar model. Singlet scalar dark matter has already been demonstrated to be a viable candidate for WIMP (Weakly Interacting Massive Particle) in literature. In the FIMP sce- nario, dark matter particles are slowly produced via “thermal freeze-in” mechanism in the early Uni- verse, and are never abundant enough to reach thermal equilibrium or to undergo pair annihila- tion inside the Universe’s plasma due to their ex- tremely small couplings. We demonstrate that for smaller couplings too, required for freeze-in pro- cess, a two component scalar dark matter model considered here could well be a viable candidate for FIMP. In this scenario, the Standard Model of particle physics is extended by two gauge singlet real scalars whose stability is protected by an un- broken Z 2 × Z ′ 2 symmetry and they are assumed to acquire no VEV after Spontaneous Symmetry Breaking. We explore the viable mass regions in the present model that is in accordance with the FIMP scenario. We also explore the upper limits of masses of the two components from the consider- ation of their self interactions. This work has been done in collaboration with Madhurima Pandey, and Debasish Majumdar. Neutron star cooling via axion emission by nucleon- nucleon axion bremsstrahlung Neutron stars generally cools off by the emission of gamma rays and neutrinos. But axions can also be produced inside a neutron star by the process of nucleon-nucleon axion bremsstrahlung. The es- cape of these axions adds to the cooling process of neutron star. We explore the nature of cooling of neutron stars including the axion emission, and compare our result with the scenario when the neu- tron star is cooled by only the emission of gamma rays and neutrinos. In our calculations we con- sider both the degenerate and non-degenerate lim- its for such axion energy loss rate, and the result- ing variation of luminosity with time and variation of surface temperature with time of the neutron star. In short, the thermal evolution of a neu- tron star is studied with three neutron star masses (1.0, 1.4, and 1.8 solar masses), and by includ- ing the effect of axion emission for different axion masses ( m a = 10 − 5 , 10 − 3 , and10 − 2 eV), and com- pared with the same when the axion emission is not considered. We compared theoretical cooling curve with the observational data of three pulsars PSR B0656+14, Geminga, and PSR B1055-52, and finally give an upper bound on axion mass limits m a ≤ 10 − 3 eV, which implies that the axion decay constant f a ≥ 0 . 6 × 10 10 GeV. This work has been done in collaboration with Avik Paul, and Debasish Majumdar. Saptarshi Mondal Unsupervised classification of galaxies. I. ICA fea- ture selection In this series of works, an objective classification of 362,923 galaxies from the Value Added Galaxy ( 201 )