sentences:  He developed the complex path method (in 1998 ) to study black hole thermodynamics which was a precursor to the `tunneling paradigm' that became quite popular later on.He is a recognized authority in the subject of the statistical mechanics of gravitating systems and was a pioneer in the systematic application of these concepts to study the gravitational clustering in an expanding universe.He has been invited to lecture twice at the Les Houches Schools (in 2002 and 2008) to a broader community about this subject.