Brane-Antibrane Systems at Finite Temperature and Phase Transition near the Hagedorn Temperature

In order to study the thermodynamic properties of brane-antibrane systems, we compute the finite temperature effective potential of tachyon T in this system on the basis of boundary string field theory. At low temperature, the minimum of the potential shifts towards T = 0 as the temperature increases. In the D9-D9 case, the sign of the coefficient of |T |2 term of the potential changes slightly below the Hagedorn temperature. This means that a phase transition occurs near the Hagedorn temperature. On the other hand, the coefficient is kept negative in the Dp-Dp case with p ≤ 8, and thus a phase transition does not occur. This leads us to the conclusion that only a D9-D9 pair and no other (lower dimensional) braneantibrane pairs are created near the Hagedorn temperature. We also discuss a phase transition in NS9B-NS9B case as a model of the Hagedorn transition of closed strings. E-mail address: [email protected] 1