Ashoke Sen, FRS, (born 1956) is an Indian theoretical physicist. He has made a number of major original contributions to the subject of string theory, including his landmark paper on strong-weak coupling duality or S-duality, which was influential in changing the course of research in the field. He pioneered the study of unstable D-branes and made the famous Sen conjecture about open string tachyon condensation on such branes. His description of rolling tachyons has been influential in string cosmology. He has also co-authored many important papers on string field theory. One of his most recent contributions include the entropy function formalism for extremal black holes and its applications to attractors. His current research interests are centered around the attractor mechanism and the precision counting of microstates for black holes in string theory. Of his nearly 200 research papers, as many as 47 papers have over 100 citations each.

Sen, now above 50, received his bachelor’s of science degree in 1975 from Calcutta University, and his master’s three years later from the Indian Institute of Technology Kanpur. He did his doctoral work in physics at Stony Brook University, where he graduated in 1982, subsequently spending the next three years as a post-doc at Fermilab and another two and a half at the Stanford Linear Accelerator Center (SLAC). In March 1988, he moved back to India and the Tata Institute of Fundamental Research. Since 1995 he has been a full professor at the Harish-Chandra Research Institute. Between 1998 and 2003, Sen visited the Isaac Newton Institute in Cambridge, U.K., as Rothschild Visiting Professor, and, between 2004 and 2005, was at MIT as Morningstar Visiting Professor. He is married to Dr. Sumathi Rao, a condensed matter physicist at HRI.