Light and Darkness: consistently coupling dark matter to photons via effective operators

TL;DR

This paper revises the theoretical treatment of fermionic dark matter interactions with photons via effective operators, emphasizing gauge invariance and its impact on experimental search interpretations across collider and detection methods.

Contribution

It demonstrates the importance of gauge invariance in effective operator models and compares the phenomenology of electromagnetic versus hypercharge couplings in dark matter searches.

Findings

Gauge-violating effects affect current experimental constraints.

Hypercharge coupling alters the sensitivity of LHC and detection experiments.

Dimension-5 operators are tightly constrained by direct detection.

Abstract

We revise the treatment of fermionic dark matter interacting with photons via dimension-5 and -6 effective operators. We show how the application of the effective operators beyond their validity introduces unphysical, gauge violating effects that are relevant for current experimental searches. Restoring gauge invariance by coupling dark matter to the hypercharge gauge field has implications for the parameter space above and below the electroweak scale. We review the phenomenology of these hypercharge form factors at the LHC as well as for direct and indirect detection experiments. We highlight where the electromagnetic and hypercharge descriptions lead to wildly different conclusions about the viable parameter space and the relative sensitivity of various probes. These include a drastic weakening of vector bosons fusion versus mono-jet searches at the LHC, and the incorrect impression that indirect searches could lead to better constraints than direct detection for larger dark matter masses. We find that the dimension-5 operators are strongly constrained by direct detection bounds, while for dimension-6 operators LHC mono-jet searches are competitive or performing better than the other probes we consider.