Paper detail

Large D gravity and low D strings

We point out that in the limit of large number of dimensions a wide class of non-extremal neutral black holes has a universal near horizon limit. The limiting geometry is the two-dimensional black hole of string theory with a two-dimensional target space. Its conformal symmetry explains properties of massless scalars found recently in the large D limit. In analogy to the situation for NS fivebranes, the dynamics near the horizon does not decouple from the asymptotically flat region. We generalize the discussion to charged black p-branes. For black branes with string charges, the near horizon geometry is that of the three-dimensional black strings of Horne and Horowitz. The analogies between the alpha' expansion in string theory and the large D expansion in gravity suggest a possible effective string description of the large D limit of black holes. We comment on applications to several subjects, in particular to the problem of critical collapse.