BPS bound states of D0-D6 and D0-D8 systems in a B-field

The D0-D6 system, which is not supersymmetric in the absence of a NeveuSchwarz B-field, becomes supersymmetric if a suitable constant B-field is turned on. On one side of the supersymmetric locus, this system has a BPS bound state, and on the other side it does not. After compactification on T ⁶, this gives a simple example in which the number of 1/8 BPS states jumps as the moduli of the compactification are changed. The D0-D8 system in a B-fleld has two different supersymmetric loci, only one of which is continuously connected to the familiar supersymmetric D0-D8 system without a B-fleld. In a certain range, the D0-D8 system also has a BPS bound state. In the limit in which the B-field goes to infinity, supersymmetric D0-D6 and D0-D8 systems and their bound states can be studied using non-commutative Yang-Mills theory.