Black holes in string theory

In chapter one, we summerize the recent developments of black holes in string theory. We focus on the issue of understanding the black hole entropy from counting microstates, but also briefly discuss the issue of understanding Hawking radiation from calculation in weak coupling and the more recent AdS/CFT correspondence. Next we present three specific studies in this area.; In chapter two, we examine the geometry near the event horizon of a family of black string solutions with traveling waves. It had previously been shown that the metric is continuous there. Contrary to expectations, we find that the geometry is not smooth, and the horizon becomes singular whenever a wave is present. Both five-dimensional and six-dimensional black strings are considered with similar results.; In chapter three, we consider the entropy of near extrernal black holes with multiple charges in the context of the correspondence principle of Horowitz and Polchinski, including black holes with two, three and four Ramond-Ramond charges. We find that at the matching point the black hole entropy can be accounted for by massless open strings ending on the D-branes for all cases except a black hole with four Ramond-Ramond charges, in which case a possible resolution in terms of brane-antibrane excitations is considered.; In chapter four, we present a class of two-charged intersecting brane solutions of the D = 11 supergravity, which contain the M2-brane, M5-brane, Kaluza-Klain monopole or Brinkmann wave as their building blocks. These solutions share the common feature that one charge is smeared out or uniform over all spatial directions occupied by the branes or waves, while the other charge is fully localized in them.