Crossing symmetry is a fundamental property in relativistic quantum field theory stating that scattering amplitudes for processes involving incoming and outgoing particles transform predictably when external particles are analytically continued between the physical particle spectrum (incoming) and antiparticle spectrum (outgoing). This principle relies on the formal convention of treating all external momenta as ingoing with positive energy-time components, where outgoing status is denoted by negative time values in the mathematical expression while maintaining Lorentz invariance. Within the domain of high-energy particle physics, this concept unifies diverse scattering processes into a single analytic function dependent on Mandelstam variables ($s$, $t$, $u$), eliminating redundant diagrams and establishing kinematic relationships valid for both scalar fields and spin-carrying particles like photons or gluons.
Crossing symmetry is a fundamental property in relativistic quantum field theory stating that scattering amplitudes for processes involving incoming and outgoing particles transform predictably when …