A Finite-Temperature Periodic Structure in (SUPER)STRING Theory
  Using a Laurent series representation for the (super)string one-loop free energy, an explicit form for the analytic continuation of the Laurent series beyond the critical (Hagedorn) temperature is obtained. As an additional result, a periodic structure is found in (super)string thermodynamics. A brief physical discussion about the origin and meaning of such structure is carried out. 
A.A. Bytsenko, E. Elizalde, S.D. Odintsov and S. Zerbini