Appendix A Conventions For brevity four-vectors are often written without a Lorentz index, that is, it is to be un- derstood that x = ( x 0 , x 1 , x 2 , x $^{3}$). When used, three-vectors are denoted as x = ( x 1 , x 2 , x $^{3}$). The following convention is used for the four-dimensional Minkowski space metric: In d -dimensions, the metric is defined such that g $^{µν}$g$_{µν}$ = d . The Einstein summation conven- tion is assumed on all indices, that is, a product containing repeated spinor, colour, Lorentz or SU(3) indices is summed over the full range of the indices. Apart from Lorentz indices, no distinction is made between raised and lowered indices. That is, A a µ = A$_{µ a}$ , for instance. We use the conventions of Ref. [24] for the Dirac gamma matrices. In what follows each matrix element is itself a two by two matrix ( i.e. the two by two identity matrix is denoted as 1). The specific forms are from which it follows that ( γ$_{5}$ ) 2 = 1. Ref. [39] discusses various approaches to defining γ$_{5}$ 104 γ 5 = iγ $^{0}$γ$^{1}$γ$^{2}$γ3 =    0 1 1 0    , (A.3) γ 0 =    1 0 0 − 1    , γ i =    0 σ i − σ i 0    , i = { 1 , 2 , 3 } , (A.2) g$_{µν}$ =       1 0 0 0 0 − 1 0 0 0 0 − 1 0 0 0 0 − 1       , g$_{µν}$ p $^{µ}$kν = p · k = p $^{0}$k0 − p · k . (A.1) where σ i is a Pauli matrix. In these conventions,