On his academic visit to Canada, Professor Govindarajan T R, Visiting Professor, Physics delivered a talk on ‘Fuzzy dark matter and primordial black hole’ at McGill University, Montreal on 15 July 2025 and ‘Overluminous Supernovae and Hubble tension’ at Perimeter Institute for Theoretical Physics, Waterloo on 21 July 2025.
Fuzzy dark matter and primordial black hole
The center of most galaxies have a super massive black hole whose presence has remained a mystery. Now we have evidence that galaxies existed as early as 400 million years after the big bang. At the same time 90% of galaxy mass is made up of dark matter. This also posed problems in identifying the nature of the particle which does not interact with normal matter except through gravity. But it aids in the formation and stability of the galaxy. Ultralight particles are one of the promising candidates. We propose one such candidate which can at the same time provide some link to understand the supermassive black holes through providing seeds for primordial blackholes.
Overluminous Supernovae and Hubble tension
Type Ia supernovae (SNe\,Ia) serve as crucial cosmological distance indicators due to their empirical consistency in decline rates with peak luminosity. This facilitates finding $H_0$. Nevertheless, a statistically significant difference persists between $H_0$ values derived from early and late-time measurements, a phenomenon known as the Hubble tension. Furthermore, recent observations have identified a subset of over-luminous SNe\,Ia, characterized by peak luminosities exceeding the nominal range and faster decline rates. These discoveries raise questions regarding the reliability of SNe\,Ia as standard candles in measuring cosmological distances. We present the Bayesian analysis of over-luminous SNe\,Ia and show that they yield lower $H_0$ estimates, exhibiting closer concordance with $H_0$ estimates derived from early-universe data. This investigation potentially represents a step toward addressing the Hubble tension.