D1/D5 system with B-field, noncommutative geometry and the CFT of the Higgs branch

The D1/D5 system is considered in the presence of the NS B field, An explic it supergravity solution in the asymptotically flat and near horizon limits is presented. Explicit mass formulae are presented in both cases. This sol ution has no D3 source branes and represents a true bound state of the D1/D 5 system, We study the motion of a separated D1-brane in the background geo metry described above and reproduce the Liouville potential that binds the D1 brane. A gauge theory analysis is also presented in the presence of Faye t-Iliopoulos (FI) parameters which can be identified with the self-dual par t of the NS B field, In the case of a single D5-brane and an arbitrary numb er of D1-branes we can demonstrate the existence of a bound state in the Hi ggs branch. We also point out the connection of the SCFT on the resolved Sy mQ(1)Q(5) ((T) over tilde(4)) with recent developments in non-commutative Y ang-Mills theory. (C) 2000 Elsevier Science B.V. All rights reserved.