Multi-Regge-Kinematic

The Multi-Regge-Kinematic (MRK) limit for $2 \rightarrow n$ parton scattering may be expressed mathematically in terms of the rapidities $y_i$ of the partons as:

$y_1 \gg y_2 \dots \gg y_n\; \quad k_{\perp,i} \sim k_\perp \forall i.$