Aspects of string thermodynamics

Abstract

In this thesis, we study thermodynamics of closed strings and open strings on D-branes in the microcanonical ensemble. Both single string and multi-string density of states are obtained from energy spectrum. In the microcanonical description, the temperature always become smaller than the limiting Hagedorn temperature, reaching it in the infinite energy limit. The stability of both systems are verified in the microcanonical picture. We also determine the early time cosmic evolution sourced by open strings on D-branes. The energy-momentum tensor of this system is determined from the thermodynam,cal data and the field equations are determined from consistency using Bianchi identities. We observe that although pressures are large, they can be ignored in field equations compared to energy. This simplifies field equations a lot and an approximate but analytic solution can be obtained.