OPEN STRING THERMODYNAMICS AND D-BRANES

We study the thermodynamics of open superstrings in the presence of p- dimensional D-branes. We get some finite temperature dualities relatin g the one-loop canonical free energy of open strings to the self-energ y of D-branes at dual temperature. For the open bosonic string the inv erse dual temperature is, as expected, the dual length under T-duality , 4 pi(2) alpha'/beta. On the contrary, for the SO(N), type-I superstr ing the dual temperature is given by beta-duality, 2 pi(2) alpha'/beta . We also study the emergence of the Hagedorn singularity in the dual description as triggered by the coupling of the D-brane to unphysical tachyons as well as the high temperature limit.