Exotic black holes

We study exotic black holes, which are new types of black holes obtained from unified theories. The exotic black holes we discussed here are classified into two; one is those with dilaton field, and the other contains non-Abelian "gauge" fields. We discuss their thermodynamical properties and evolutions. The farmer shows that the superstring predicts a critical dilaton coupling to U(1) field such that the Hawking radiation changes completely beyond the critical value and it diverges in the extreme limit. As a result, a naked singularity may appear at the end of evaporation process for models with larger coupling than the critical value. The second type of exotic black holes give non-trivial black holes, which have the first type of hair. Since some of them are stable, this can be regarded as counterexamples of no hair conjecture. The specific heat will change the sign a few times for some range of parameters. The fate of those black holes are as follows:(1) The unstable black holes will becomes the other stable ones including Schwarzschild black hole. (2) The neutral black holes with the "effective mass" of non-Abelian fields have the upper bound of the black hole mass and when the black hole evolves beyond this critical value, it shifts to more stable Schwarzschild black hole. If the black hole evaporates via the Hawking radiation, the stable particle will remain. (3) For the charged black hole such as monopole black hole, since the Reissner-Nordström black hole below some critical mass becomes unstable and there is no Schwarzschild black hole, the monopole black hole is a unique and stable black hole in some range of parameters. When the black hole gets the mass via accretion, it will become the Reissner-Nordström trivial black hole, while when it evaporates via the Hawking radiation, the stable regular monopole will remain.