FEYN CALC SYMBOL

SetMandelstam


defines the Mandelstam variables s=(p1+p2)^2, t=(p1+p3)^2, u=(p1+p4)^2 and sets the momenta on-shell: p1^2=m1^2, p2^2=m2^2, p3^2=m3^2, p4^2=m4^2. Notice that p1+p2+p3+p4 = 0 is assumed. SetMandelstam[x, {p1, p2, p3, p4, p5}, {m1, m2, m3, m4, m5}] defines x[i, j] = (pi+pj)^2 and sets the momenta on-shell. p1+p2+p3+p4 = 0 is assumed.