Mandelstam variables
= Mandelstam variables
{c}
{wiki}
= Mandelstam invariant
{c}
{synonym}
For two-to-two scattering $A+B\to C+D$,
$$
s=(P_A+P_B)^2,\qquad
t=(P_A-P_C)^2,\qquad
u=(P_A-P_D)^2.
$$
They satisfy $s+t+u=m_A^2+m_B^2+m_C^2+m_D^2$ in units $c=1$.