Finite Temperature Systems of Brane-Antibrane Pairs and Non-BPS D-branes

We investigate the thermodynamic properties of D-brane−anti-D-brane pairs and non-BPS D-branes on the basis of boundary string field theory. We calculate the finite temperature effective potential of N pairs of D-brane−anti-D-brane in the non-compact background and in the toroidal background. In the noncompact background case, a phase transition occurs slightly below the Hagedorn temperature, and the D9-D9 pairs become stable. Moreover, the total energy at the critical temperature decreases as N increases as long as the ’t Hooft coupling is very small. This leads us to the conclusion that the large N pairs of D9D9 are created near the Hagedorn temperature at the same time. In the toroidal background case (M1,9−D×TD), a phase transition occurs only if the Dp-Dp pair is extended in all the non-compact directions as long as the ’t Hooft coupling is very small. The total energy at the critical temperature also decreases as N increases. We also calculate the finite temperature effective potential of non-BPS D-branes, and we obtain the similar results. Then we consider the thermodynamic balance between open strings on these branes and closed strings in the bulk in the ideal gas approximation, and conclude that most of the total energy is dominated by the open strings. E-mail address: [email protected] 1