BPS states and Supersymmetry

Podge_irl

I've a quick question which I'm hoping someone (meaning Prof Fink probably!) can help me with. I'm looking at BPS monopoles in N=2 SYM theory and trying to show that they break half the supersymmetries. We can set the fermions to zero initially so that that bosonic variations are automatically zero so we only have the fermionic variations, which are (after some annoying algebra)

d\psi = \gamma_5\Gamma_k D_k \phi (1-\Gamma_5)\epsilon

where the \Gamma's generate a Euclidean Clifford algebra. Now, 1-\Gamma_5 obviously projects out half the states of the spinor \epsilon. All the papers I'm reading refer to breaking half the supersymmetries, but I'm not sure I'm following what they mean (or which half is being broken). The SUSY variation d\psi can be written solely in terms of the negative chirality \epsilon, yet one of the papers I'm reading says that its the negative chirality \epsilon that are the broken supersymmetries, but I don't really follow this. The positive chirality \epsilon's don't seem to generate a SUSY variation anymore, so I would have thought that they are the ones that are broken?

Professor_Fink

I'm afraid I'm not going to be too much help here. I don't know very much about supersymmetry.