Hawking radiation in string theory and the string phase of black holes - art. no. 084030

The quantum string emission by black holes is computed in the framework of the "string analog model" (or thermodynamical approach), which is well suit ed to combine quantum-field theory (QFT) and string theory in curved backgr ounds (particularly here, as black holes and strings possess intrinsic ther mal features and temperatures). The QFT-Hawking temperature T-H is upper bo unded by the string temperature T-S in the black hole background. The black hole emission spectrum is an incomplete gamma function of (T-H-T-S). For T -H much less than T-S, it yields the QFT-Hawking emission. For T-H-->T-S, i t shows that highly massive string states dominate the emission and undergo a typical string phase transition to a microscopic "minimal" black hole of mass M-min or radius r(min) (inversely proportional to T-S) and string tem perature T-S. The string back reaction effect [self-consistent black hole s olution of the semiclassical Einstein equations with mass M+ (radius r(+)) and temperature T+] is computed. Both the QFT and string black hole regimes are well defined and bounded: r(min)less than or equal to r(+)less than or equal to r(S), M(min)less than or equal to M(+)less than or equal to M, le ss than or equal to M, T(H)less than or equal to T(+)less than or equal to T-S. The string "minimal" black hole has a life time tau(min) similar or eq ual to(k(B)c/G (h) over bar) T-S(-3).