Unitarisation of EFT Amplitudes for Dark Matter Searches at the LHC

TL;DR

This paper introduces a K-matrix unitarisation method for EFT analyses in LHC dark matter searches, enabling more reliable cross section estimates and bounds on operator cut-off scales at high energies.

Contribution

It presents a novel unitarisation approach for EFT amplitudes in dark matter searches, improving the reliability of bounds on new physics parameters.

Findings

Unitarisation provides more stringent bounds than truncation in certain parameter regions.

The method ensures perturbative unitarity at high energies.

Application to D5 operator in monojet searches demonstrates its effectiveness.

Abstract

We propose a new approach to the LHC dark matter search analysis within the effective field theory (EFT) framework by utilising the K-matrix unitarisation formalism. This approach provides a reasonable estimate of the dark matter production cross section at high energies, and hence allows reliable bounds to be placed on the cut-off scale of relevant operators without running into the problem of perturbative unitarity violation. We exemplify this procedure for the effective operator D5 in monojet dark matter searches in the collinear approximation. We compare our bounds to those obtained using the truncation method and identify a parameter region where the unitarisation prescription leads to more stringent bounds.