Improved limits for Higgs-portal dark matter from LHC searches

TL;DR

This paper refines the constraints on Higgs-portal dark matter models by accurately evaluating the Higgs-nucleon coupling, incorporating pion-exchange effects, and demonstrating the importance of nuclear physics in interpreting collider and direct detection limits.

Contribution

It provides a new, more precise calculation of the Higgs-nucleon coupling, including two-nucleon effects, reducing previous uncertainties and improving dark matter search limits.

Findings

Higgs-nucleon coupling f_N = 0.308(18)

Two-nucleon contributions are negligible due to cancellation

Uncertainty in Higgs-nucleon coupling was previously overestimated

Abstract

Searches for invisible Higgs decays at the Large Hadron Collider constrain dark matter Higgs-portal models, where dark matter interacts with the Standard Model fields via the Higgs boson. While these searches complement dark matter direct-detection experiments, a comparison of the two limits depends on the coupling of the Higgs boson to the nucleons forming the direct-detection nuclear target, typically parameterized in a single quantity $f_N$. We evaluate $f_N$ using recent phenomenological and lattice-QCD calculations, and include for the first time the coupling of the Higgs boson to two nucleons via pion-exchange currents. We observe a partial cancellation for Higgs-portal models that makes the two-nucleon contribution anomalously small. Our results, summarized as $f_N=0.308(18)$, show that the uncertainty of the Higgs-nucleon coupling has been vastly overestimated in the past. The improved limits highlight that state-of-the-art nuclear physics input is key to fully exploiting experimental searches.