INFLUENCE ON SPACETIME STRUCTURE OF QUANTUM BACK REACTION

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Firstly, evaporation of the black hole due to Hawking radiation has been investigated in models that extract most essential features of the black hole geometry ; existence of the event horizon. By taking either a two dimensional dilaton gravity or the moving mirror model that mimics essence of the Hawking radiation, it was shown that the black hole can completely disappear without furthere radiation, but leaving behind stable remnants. In the second project the problem of coherent field oscillation accompanying particle production has been studied. The behavior of the quantum system described by bose quantum fields coupling to the classical oscillator field was shown to be analyzed vigorously by using a functional Schrodinger picture. The short time average over a few oscillation periods exhibits particle production taking place in infinitely many band regions in the parameter space of the particle wave number and the oscillation amplitude, known as the band of parametric resonance. Accordingly the navive estimate due to the perturbative Born rate is grossly wrong for an initial large amplitude oscillation. This has important effects hitherto ignored on the reheating problem after inflation and the Polonyi problem in supergravity models ; inflation may end with intermediate epoch of much higher temperatures that realizes readily the GUT baryogenesis at the same time suppressing production of gravitino required by successful nucleosynthesis.