The D2-D6 system and a fibered AdS geometry

The system of D2-branes localized on or near D6-branes is considered. The w orld-volume theory on the D2-branes is investigated, using its conjectured relation to the near-horizon geometry. The results are in agreement with kn own facts and expectations for the corresponding field theory and a rich ph ase structure is obtained as a function of the energy scale and the number of branes. In particular, for an intermediate range of the number of D6-bra nes, the IR geometry is that of an AdS(4) space fibered over a compact spac e. This D2-D6 system is compared to other systems, related to it by compact ification and duality and it is shown that the qualitative differences have compatible explanations in the geometric and field-theoretic descriptions. Another system - that of NS5 branes located at D6-branes - is also briefly studied, leading to a similar phase structure. (C) 1999 Elsevier Science B .V. All rights reserved.