Shyam, A philosophically astute study that concentrates on Abhinavagupta (his theory of drama, aesthetics, etc.) which also deals with rasa theory is J. Moussaieff Masson's _Santarasa and Abhinavagupta's Philosophy of Aesthetics_ Bhandarkar Research Institute, 1969. It's out of print, but should be available at a good university library or by interlibrary loan. Dan Lusthaus