Revisiting Scalar and Pseudoscalar Couplings with Nucleons

TL;DR

This paper reevaluates scalar and pseudoscalar couplings of nucleons considering recent lattice results, showing that strange quark contributions are smaller than previously estimated, which impacts dark matter detection models.

Contribution

It provides updated calculations of nucleon couplings incorporating recent lattice QCD findings, refining the understanding of quark contributions to nucleon interactions.

Findings

Strange quark contributions to nucleon couplings are smaller than earlier estimates.

Revised nucleon matrix elements lead to lower predicted cross sections for dark matter interactions.

Sizable SU(3) breaking effects influence axial-vector coupling constants.

Abstract

Certain dark matter interactions with nuclei are mediated possibly by a scalar or pseudoscalar Higgs boson. The estimation of the corresponding cross sections requires a correct evaluation of the couplings between the scalar or pseudoscalar Higgs boson and the nucleons. Progress has been made in two aspects relevant to this study in the past few years. First, recent lattice calculations show that the strange-quark sigma term $\sigma_s$ and the strange-quark content in the nucleon are much smaller than what are expected previously. Second, lattice and model analyses imply sizable SU(3) breaking effects in the determination on the axial-vector coupling constant $g_A^8$ that in turn affect the extraction of the isosinglet coupling $g_A^0$ and the strange quark spin component $\Delta s$ from polarized deep inelastic scattering experiments. Based on these new developments, we re-evaluate the relevant nucleon matrix elements and compute the scalar and pseudoscalar couplings of the proton and neutron. We also find that the strange quark contribution in both types of couplings is smaller than previously thought.