O Quantum Fluctuations and Black Holes

We explore some exotic phenomena in charged black holes, arising from the second quantization of matter fields or from the first quantization of fundamental strings. Spherically symmetric magnetic black holes admit special modes of electrically charged fermions, known as Callan-Rubakov modes, which can be quantized efficiently. We find that the chargeless sector generates non-thermal quantum radiations from extremal Reissner-Nordstrom black holes, thereby reducing the black hole masses below the familiar classical bound in spite of the vanishing Hawking temperature. On the other hand, the charged sector induces a vacuum energy distribution and the gravitational backreaction thereof, which are particularly pronounced for extremal dilatonic black holes. Implications of these quantum effects are studied in great detail. Also considered is a string-inspired two-dimensional gravity with nonsingular charged black holes among its solutions. After a lengthy discussion on the stability of these novel space -times, we speculate on the possibility and implications of nonsingular black holes in full-blown string theories.