Bounds on Crossing Symmetry

Understand

Proposed in 1954 by Gell-Mann, Goldberger, and Thirring, crossing symmetry postulates that particles are indistinguishable from anti-particles traveling back in time.

• Its elusive proof amounts to demonstrating that scattering matrices in different crossing channels are boundary values of the same analytic function, as a consequence of physical axioms such as causality, locality, or unitarity.
• In this work we report on the progress in proving crossing symmetry on-shell within the framework of perturbative quantum field theory.
• We derive bounds on internal masses above which scattering amplitudes are crossing-symmetric to all loop orders.