35th Annual Report (2022-2023) - ENGLISH

164 Areasofresearch: Researchworks: The ICARD at Department of Physics, Gauhati University was active from October 2022. It hosts research activities in gravitation & cosmology and observational astronomy. The department has two permanent faculty members in the field of Astronomy & Astrophysics. They are Sanjeev Kalita and Biman J Medhi. Currently there are 7 PhD students working in this field. They are provided with a dedicated research lab for their studies. The lab is equipped with networking facilities. Sanjeev Kalita is involved in the study of gravitation and cosmology and Biman J Medhi is involved in observational astronomy. The department also runs the Gauhati University Observatory for students' training in observational astronomy and public viewing of celestial objects. In the field of gravitation and cosmology the following problems have been studied – (i) effect of dark matter distribution on modified gravity parameters near the Galactic Centre (GC) black hole, (ii) testability of f(R) gravity near the GC black hole through pericentre shift of orbits below S0-2 and (iii) constraining several spacetime metrics through the observed shadow of the GC black hole. In the first problem, exponential and power law dark matter profiles near the GC black hole were considered. By estimating the f(R) gravity scaIaron field amplitude and gravitational potential near the black hole it was found that dark matter distribution can affect the screening and unscreening of f(R) scalarons. Low dark matter density naturally unscreens scalarons and high dark matter density screens the scalarons. It was found to be independent of the black hole spin. In the second study, difference 2 between R gravity and general relativity has been studied through pericentre shift of stellar orbits near the GC black hole. Effect of general relativity was found to be suppressed towards compact stellar orbits. In general f(R) models, scalarons with – 16 masses 10 eV are found to be screened –22 and scalarons withmass range 10 ev – 10 – 19 eV are found to be unscreened near the orbit of S0-2. Testability of these scalarons through upcoming observations of Extremely Large Telescopes has been studied. In the problem of black hole shadow, the measured angular size of the shadow of the GC black hole has been used to constrain Kerr/Schwarzschild –de Sitter (KdS and SdS) metric, Reissner-Nordstrom (RN) metric with tidal charge and scalaron induced metric. Constraints on KdS, SdS and RN metric has been found to be stringent relative to M87* shadow. The 8. Cosmological implications of an interactingmodel of darkmatter & dark energy; K.R. Mishra, S.K.J. Pacif, R. Kumar , K. Bamba; Physics of the Dark Universe 40, 101211, 2023. 9. Dynamics of uniformly collapsing system and the horizon formation; A. Jaiswal, S.K. Srivastava, R. Kumar ; International Journal of Geometric Methods in Modern Physics, 2350114, 2023. 10. Spherically symmetric collapsing star with the background of dark energy; G. Verma, R. Kumar , K.R. Mishra; International Journal of Geometric Methods in Modern Physics 19 (10), 2250148, 2022. 11. A dynamical model of radiating stars and their thermal behavior; G. Verma, R. Kumar ; The European Physical Journal C, 82 (6), 513, 2022. 12. A new class of spherically symmetric gravitational collapse; R Kumar , A Jaiswal, Theoretical and Mathematical Physics 211 (1), 558-566, 2022. 13. Study of vibrational spectra of polycyclic aromatic hydrocarbons with phenyl side group; A. Maurya, R. Singh, S. Rastogi , J.Molecular Spectroscopy, 391, 111720, 2023. 14. I n v e s t i ga t i on o f a tmo s phe r i c turbulence and scale lengths using radiosonde measurements of GVAX- campaign over central Himalayan region; A. Rajput, N. Singh, J. Singh, S. Rastogi , J. Atmospheric and Solar- Terrestrial Phys., 235, 105895, 2022. 1. Dr. Aditya Vaishya, Ahmedabad University, visited ICARD between 4 – 8 Activities/Outreachprogrammes: June 2022 for discussions regarding Aerosol observations fromGorakhpur. 2. Prof. Amit Pathak , BHU, Varanasi, visited on 11 June 2022 and gave lecture on Astrochemistry for MSc final students. 3. Prof. Dipankar Banerjee, ARIES, Nainital, visited on 5-6 December 2022, for discussions related to ongoing MoU between ARIES and DDUGU. Motivational interaction session with MSc students was organized. 4. Prof. Shibesh K. Jas Pacif, SGT University, Gurugram, delivered popular lecture on 'Structure of the Universe', Department of Mathematics and Statistics, DDUGU on 4 February 2023. Coordinator: Dr. Sanjeev Kalita ICARD Department of Physics, Gauhati University, Guwahati, Assam: Activities from 01 April 2022 till 31 March 2023