About some exact solutions for 2+1 gravity coupled to gauge fields

Some exact static solutions for Einstein gravity in 2+1 dimensions coupled to abelian gauge field are discussed. Some of these solutions are three-dimensional analogs of the Schwarzschild black holes. The metrics in the regions inside and outside the horison are connected by the changing of the Planck mass sign.Comment: 10 page

DBI Action from Closed Strings and D-brane second Quantization

Brane-like vertex operators play an important role in a worldsheet formulation of D-branes and M-theory. In this paper we derive the DBI D-brane action from NSR closed string sigma-model with brane-like states. We also show that these operators carry RR charges and define D-brane wavefunctions in a second quantized formalism.Comment: 16 pages, latex, typos corrected, BRST nontriviality condition (9) for closed string vertices is amende