
Discontinuity
Discontinuity[s] is a setting for Part to LoopRefine to compute the discontinuity across the normal threshold cut in channel .
Discontinuity[s,t] computes the Mandelstam double spectral function in overlapping channels and .
 Gives discontinuities across branch cuts of PVA, PVB, PVC, and PVD. Poles are ignored.
 The output is always proprtional to the HeavisideTheta function which has support only when the channel is open.
 Channels of PassarinoVeltman functions are identified by matching patterns s and t to entire arguments of PVA, PVB, PVC, and PVD.
 A correct result is guaranteed only if all other channels are closed (below normal threshold).
 Internally, a channel marker is placed in the appropriate arguments of PVA, PVB, PVC, and PVD, and a much simplified form of the PassarinoVeltman reduction formula is applied to obtain the result.
Calculate the discontinuity across the normal threshold cut of the scalar twopoint function:
