SPLP[p,q,n,nb] denotes the positive component in the lightcone decomposition of the scalar product p \cdot q along the vectors n and nb. It corresponds to \frac{1}{2} (p \cdot n) (q \cdot \bar{n}).
If one omits n and nb, the program will use default vectors specified via $FCDefaultLightconeVectorN and $FCDefaultLightconeVectorNB.
Overview, Pair, FVLN, FVLP, FVLR, SPLN, SPLR, MTLP, MTLN, MTLR.
SPLP[p, q, n, nb]\frac{1}{2} \left(\overline{n}\cdot \overline{p}\right) \left(\overline{\text{nb}}\cdot \overline{q}\right)
StandardForm[SPLP[p, q, n, nb] // FCI]\frac{1}{2} \;\text{Pair}[\text{Momentum}[n],\text{Momentum}[p]] \;\text{Pair}[\text{Momentum}[\text{nb}],\text{Momentum}[q]]
Notice that the properties of n and nb vectors have to be set by hand before doing the actual computation
SPLP[p1 + p2 + n, q, n, nb] // ExpandScalarProduct\frac{1}{2} \left(\overline{\text{nb}}\cdot \overline{q}\right) \left(\overline{n}\cdot \overline{\text{p1}}+\overline{n}\cdot \overline{\text{p2}}+\overline{n}^2\right)
FCClearScalarProducts[]
SP[n] = 0;
SP[nb] = 0;
SP[n, nb] = 2;SPLP[p1 + p2 + n, q, n, nb] // ExpandScalarProduct\frac{1}{2} \left(\overline{\text{nb}}\cdot \overline{q}\right) \left(\overline{n}\cdot \overline{\text{p1}}+\overline{n}\cdot \overline{\text{p2}}\right)
FCClearScalarProducts[]