I am an alumnus of the Indian Institute of Technology, Kharagpur (1969-74) and received my PhD (1982) at the Tata Institute of Fundamental Research, Bombay, where I was a staff member 1979-84. Subsequently I held visiting positions at CERN, Oxford Astrophysics, Rutherford Appleton Laboratory, and worked in science education for the NGO Eklavya, Bhopal. Since 1990 I have been at the Rudolf Peierls Centre for Theoretical Physics, Oxford - as Glasstone Research Fellow, then PPARC Advanced Fellow, appointed Lecturer in 1998 and Professor in 2006. I was Head of the Particle Theory Group (2011-19) and Niels Bohr Professor at Copenhagen (2013-18). I am Emeritus Fellow of Linacre College, Oxford. My interests lie at the interface of fundamental physics with astrophysics and cosmology: big bang nucleosynthesis, dark matter, dark energy, inflation & the cosmic microwave background, relic topological defects, weak interactions & neutrinos etc. I also work on high energy cosmic rays, gamma-rays & neutrinos, and belong to the IceCube Neutrino Observatory and the Cherenkov Telescope Array collaborations. (Earlier I worked on the Pierre Auger Observatory and the CERN BEBC Beam Dump.) I participate in laboratory experiments using high powered lasers to investigate astrophysical processes, and programmes on Quantum Sensors for Fundamental Physics as well as Rubin-LSST.