Implications of unitarity and gauge invariance for simplified dark matter models

TL;DR

This paper examines how simplified dark matter models often violate gauge invariance and unitarity, and how fixing these issues reveals richer phenomenology and stronger experimental constraints.

Contribution

It highlights the importance of gauge invariance and unitarity in dark matter models and explores the implications of restoring these principles for phenomenology and experimental constraints.

Findings

Gauge invariance imposes strong constraints from dilepton searches.

Restoring unitarity introduces new states affecting interactions.

Constraints often surpass traditional monojet limits.

Abstract

We show that simplified models used to describe the interactions of dark matter with Standard Model particles do not in general respect gauge invariance and that perturbative unitarity may be violated in large regions of the parameter space. The modifications necessary to cure these inconsistencies may imply a much richer phenomenology and lead to stringent constraints on the model. We illustrate these observations by considering the simplified model of a fermionic dark matter particle and a vector mediator. Imposing gauge invariance then leads to strong constraints from dilepton resonance searches and electroweak precision tests. Furthermore, the new states required to restore perturbative unitarity can mix with Standard Model states and mediate interactions between the dark and the visible sector, leading to new experimental signatures such as invisible Higgs decays. The resulting constraints are typically stronger than the 'classic' constraints on DM simplified models such as monojet searches and make it difficult to avoid thermal overproduction of dark matter.