The strangeness content of the nucleon

TL;DR

This paper investigates the strangeness content of the nucleon, relevant for neutralino–nucleon scattering cross sections in dark matter searches. It uses lattice QCD with Wilson-like fermions and the Feynman-Hellmann theorem to relate scalar matrix elements to derivatives of the nucleon mass with respect to valence and sea-quark masses, revealing mixing between connected and disconnected contributions. The key result is that naive lattice estimates suggesting a large strange content are not reliable once mixing is accounted for; the lattice results are compatible with $y=0$ within errors, with a few analyses yielding $y\approx -0.3$ but statistically inconclusive. The study highlights the need for simulations with $N_f=2$ light sea quarks plus a heavier strange sea, controlled extrapolations to physical quark masses, and improved statistics to sharpen $y$ and its impact on dark matter phenomenology.

Abstract

We evaluate the matrix element of $\bar{q} q$ in hadron states on a lattice. We find substantial mixing of the connected and disconnected contributions so that the lattice result that the disconnected contribution to the nucleon is large does not imply that the $\bar{s} s$ content is large. This has implications for dark matter searches.

Figures (1)

• Figure 1: Connected and disconnected diagrams