Helicity Selection Rules and Non-Interference for BSM Amplitudes

TL;DR

This paper uncovers helicity selection rules in high-energy scattering that show SM and BSM effects often do not interfere, highlighting the importance of dimension-8 operators in effective field theories.

Contribution

It introduces a novel set of helicity selection rules that demonstrate non-interference between SM and BSM amplitudes in most 2-to-2 processes at high energy.

Findings

SM and BSM effects often do not interfere due to helicity rules

Dimension-8 operators can be as important as dimension-6 in certain regimes

Implications for the validity of EFT analyses in collider physics

Abstract

Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the SM and in the context of an effective Lagrangian description of BSM dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 to 2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach.