I was educated at the Indian Institute of Technology, Kharagpur (1969-74) and awarded 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 - first as Glasstone Research Fellow, then PPARC Advanced Fellow, appointed Lecturer in 1998 and Professor in 2006. I was Head of the Particle Theory Group during 2011-19 and Niels Bohr Professor (2013-18) at the University of Copenhagen. Presently I am adjunct professor at the Raman Research Institute, Bangalore.
My interests are at the interface of fundamental physics with astrophysics and cosmology - viz. dark matter & dark energy, inflation & the cosmic microwave background, neutrinos & other relic particles, primordial nucleosynthesis, relic topological defects etc. I also work on high energy cosmic rays, neutrinos and gamma-rays, and belong to the IceCube Neutrino Observatory & the Cherenkov Telescope Array collaborations. Previously I have worked on the Pierre Auger Observatory & the BEBC Beam Dump experiment at CERN. I participate in the Quantum Sensors for the Hidden Sector programme & in laboratory experiments using high powered lasers to investigate astrophysical processes.