36th Annual Report (2023-24)

171 IUCAA CENTRES FOR ASTRONOMY RESEARCH AND DEVELOPMENT (ICARDs) Areas of Research: ResearchworkdoneinICARD General Relativity, Theoretical Astrophysics, Compact stars, Dark matter, Alternative Theory of Gravity, Wormhole Physics, Cosmology started functioning as a host of ICARD on and from 14 September 2022 after receiving approval from the competent authority. Honorary Visiting Professor and Former Head Astro-particle Physics Division, SINP) a visiting associate of IUCAA) other associates of nearby institutions along with the research scholars of Astrophysics group are The Department of Physics, Aliah University, The Department has enhanced its Astrophysics program, introducing General Relativity, Astrophysics, and Cosmology courses in the newCBCS curricula. This shift offers M.Sc. students a comprehensive 12- credit course alongside a 4-credit project in Astrophysics and Cosmology, starting from the 2022-23 academic session. Prof. Md. Mehedi Kalam coordinates ICARD, supported by Prof. Debades Bandopadhyay ( and Dr. SajahanMolla ( , among others. The involvement of experienced professionals and active members from neighbouring institutions enriches the research environment. This transition has seen the enrollment of 17 students in 2022- 23 and 14 in 2023-24, reflecting a growing interest in these specialised fields (Activities from 01 April 2023 to 31 March 2024) The members associated with ICARD, Aliah University, have worked on different issues related to Astrophysics and Cosmology. consider an exotic matter source with a nonlinear Equation of state (EoS) and a minimally coupled scalar field with two different potentials that produce a closed inflationary emergent universe in the relativistic context. we have computed Together with other associates and members, we Also, quasi-normal modes of Ayon-Beato Garcia (ABG) Regular Black Holes (which have a non-linear electrodynamical source) using the WKB methods and AIM. A comparison has been made between the spectrum of QNMs calculated by both methods. We analyse how the spectrumof QNMs depends on the black hole parameters, multipole number and overtone number and establish that the ABG black hole is stable against the scalar field. Also, we construct a traversable static Lorentzian wormhole in the effective scenario of Loop Quantum Cosmology (LQC), where the field equations are modified due to the ultraviolet (UV) corrections introduced at large space-time curvatures. A stable wormhole can be constructed in an effective scenario without violating the null energy condition (NEC) by physical matter at the throat. The NEC is effectively violated due to the corrections in the field equations from LQC, resolving the Weyl curvature singularity at the throat. However, the physical matter violates the strong energy condition (SEC), suggesting the interesting possibility that dark energy can be harnessed into a wormhole. A possible explanation for this is the presence of inherent pressure isotropy in the UV- corrected field equations (discussed and compared to braneworld wormholes in the discussion). No additional exotic ingredient (violating NEC) is required, avoiding quantum instabilities. The tidal forces at the throat do not diverge, and the throat is found to be stable. The wormhole features an attractive geometry. LQC can resolve both the types of curvature singularities appearing at the black hole centre and wormhole throat without exoticmatter. In another article, we explored the possibility of constructing a traversable wo rmho l e on t he Sh t ano v - Sahn i braneworld with a time-like extra dimension. We find that the Weyl curvature singularity at the throat of thewormhole can be removed with physical matter satisfying the NEC ρ + p ≥ 0, even in the absence of any effective Λ -term or any charge source on the brane. (The NEC is violated by the effective matter description on the brane arising due to effects of higher dimensional gravity.) Besides satisfying NEC, the matter constituting the wormhole also satisfies the Strong Energy Condition (SEC), ρ + 3p ≥ 0, leading to the interesting possibility that normal matter on the brane may be harnessed into a wormhole. Incidentally, these conditions must also be satisfied to realise a non-singular bounce and cyclic cosmology on the brane where both past and future singularities can be averted. Thus, such a cyclic universe on the brane, constituted of normal matter, can naturally contain wormholes. The wormhole shape function on the brane with a time-like extra dimension represents the tubular structure of the wormhole spreading out at large radial distances much better than in wormholes constructed in a braneworld with a spacelike extra dimension and have considerably lower mass, resulting in minimisation of the amount of matter required to construct a wormhole. Wormholes in the Shtanov-Sahni (SS) braneworld also have sufficiently low tidal forces, facilitating traversability. Additionally, they are found to be stable and exhibit a repulsive geometry. (Activities from 01 April 2023 to 31 March 2024 C olloquium lecture delivered by Dr Assistant Research Scientist, NASA Goddard Space Flight Center Greenbelt, USA, on Friday, 09 February 2024, at 2.30 p.m. at the Seminar Room, Department of Physics, Aliah University, New Town campus. Title of the talk: Exploring the Hot and the EnergeticUniverse. Colloquia/SeminarsorganisedbyICARD Nazma Islam, Coordinator: Professor Md. Mehedi Kalam ICARD Department of Physics, Aliah University, Kolkata Activities from 1st April 2023 to 31st March 2024