Annual Report_Abridged - Second Version - FINAL

19 Mitra have developed a two stage (coincident) hierarchical search, which speeds up the search for compact binary coalesces (CBCs) by more than one order of magnitude [Phys. Rev. D 105, 064005 (2022)]. The search was applied to real data and it recovered all the events published in the LIGO-Virgo-KAGRA (LVK) collaboration's first transient catalogue (GWTC-1) with approximately the same significance. They have also developed a novel technique of determining the significance of an event accurately yet fast, without which the computational efficiencywould be lost [Phys. Rev. D 109, 024046 (2024)]. Shreejit Jadhav, Mihir Srivastava (IIT Kharagpur) and Sanjit Mitra have developed a method towards making a fully Machine Learning based search algorithm for CBCs. While the method is not yet as efficient as Matched Filtering, which is still the primary search method for these sources, it is a big step towards making a primarily Machine Learning based search. Also, it has the potential to work with the present Matched Filtering based analysis to perform a deeper search (that is, to find low significance events). [Mach. Learn.: Sci. Technol. 4 (2023) 045028]. Sanjit Mitra and his group developed an analysis pipeline, PyStoch, to search for anisotropic GWB, which utilised years' worth of data folded to one sidereal day utilising a mathematical symmetry, which was also developed by the same group. The folded data not only made the standard LVK analysis hundreds of times faster, but enabled making skymaps at every frequency bin, which was not possible before. The LVK collaboration devoted a full publication on All-Sky All-Frequency (ASAF) analysis, where Deepali Agarwal was the lead analyst, Sanjit Mitra led the search. Sukanta Bose and Shivaraj Kandhasamy were part of the LVK review team. [Phys. Rev. D105, 122001 (2022)] CosmologywithWeakGravitational Lensing The research group led by Surhud More at IUCAA has focussed on cosmology and astrophysics of the galaxy-dark matter connection using weak gravitational lensing and gravitational waves. One of the main highlights of the research from the research group include the results from the weak gravitational lensing group of the Subaru HSC survey, that measured the amplitude of density fluctuations in the Universe (More et al. 2023, Miyatake et al. 2023, Sugiyama et al 2023, Li et al 2023 and Dalal et al. 2023). The group has also worked on improving methods to use gravitational wave events to constrain the expansion history of the Universe (Abbott et al. 2023, Gray et al. 2023, Ghosh et al. 2023). The weak gravitational lensing signal from the HSC survey was used to probe the stellar mass halo mass relation of galaxies from redshift range of 0.3 to 0.8 (Chaurasiya et al. 2023), to obtain the tightest constraints on the edges of X-ray galaxy clusters from the eROSITA eFEDS survey (Rana et al. 2023), to put the first upper limits on the fraction of orphan satellite galaxies from galaxy clusters (Ratewal et al. 2023), and also to show the linear relation between the sizes of galaxies and the sizes of their dark matter halos (Mishra et al. 2023) for the first time using gravitational lensing. The research also included a method to constrain the asteroid mass primordial black holes using parallax lensing of GRBs (Gawade et al. 2023). Computational Astrophysics with High PerformanceComputing Dipanjan Mukherjee and his collaborators are mainly interested in investigating diverse