engleski

Black holes in heterotic string theory

There is a hope that understanding of black hole (BH) properties could give us important insight into the structure of space-time (i.e., "quantum gravity"). Especially puzzling is the question of microscopic explanation of black hole entropy. For some special classes of BH's string theory is providing the answer, where the BH is an ensamble of perturbative excitations of D-brane configurations. In this talk we review some recent results for BH's in heterotic string theory, mainly taking as examples 2-charge and 4-charge BH's, and explain concepts and methods such as attractor mechanism, entropy function formalism or uses of AdS_3/CFT_2 in combination with anomaly matching. Emphasis will be on the influence of the higher-order corrections in string tension alpha' in effective action. We separate BH's in two types - large and small. Large BH's have finite horizon area (so also the entropy) already in the supergravity approximation (lowest order in alpha'), which means they can be treated perturbatively in alpha'. We explicitly show how one obtains matching between string and gravity results up to order of alpha'^3. Situation with small black holes is even more interesting. In the supergravity approximation they have singular horizon with vanishing area, which becomes regular after including alpha' string corrections, but with the radius (in string frame) of the order alpha'. This means that low energy effective action is not expected to be valid for near horizon description. Curiously, some actions with finite number of terms, like Gauss-Bonnet or Wilsonian SUGRA cutted to second order, succesfully predict the entropy formula not only for small, but also for pletora of large BH's. We show that there is a simple action of the Lovelock type (consisting of extended Gauss-Bonnet densities) which gives result for the entropy of 2-charge BH's which exactly matches microscopic string result in all dimensions D>=4. We also present some new results for BH's in five dimensions.

black holes; string theory

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