Abstract
We calculate the scalar and tensor charges of the nucleon in 2+1-flavor lattice QCD, for which the systematics of the renormalization of the disconnected diagram is well controlled. Numerical simulations are performed at a single lattice spacing a = 0.11 fm. We simulate four pion masses, which cover a range of $m_\pi \sim$ 290 - 540 MeV, and a single strange quark mass close to its physical value. The statistical accuracy is improved by employing the so-called low-mode averaging technique and the truncated solver method. We study up, down, and strange quark contributions to the nucleon charges by calculating disconnected diagrams using the all-to-all quark propagator. Chiral symmetry is exactly preserved by using the overlap quark action to avoid operator mixing among different flavors, which complicates the renormalization of scalar and tensor matrix elements and leads to possibly large contamination to the small strange quark contributions. We also study the nucleon axial charge with contribution from the disconnected diagram. Our results are in reasonable agreement with experiments and previous lattice studies.
Highlights
The nucleon charges are very important input parameters in the study of new physics beyond the standard model, and accurate values are required in phenomenological analyses
For the disconnected diagrams calculated in this study, we observe that a large part of their statistical error comes from a piece which is the product of the low-mode component of the nucleon propagator and the high-mode part of the quark loop
We present our calculation of the nucleon scalar, axial, and tensor charges in Nf 1⁄4 2 þ 1 flavor QCD
Summary
The nucleon charges are very important input parameters in the study of new physics beyond the standard model, and accurate values are required in phenomenological analyses. Exact chiral symmetry preserved by the overlap action suppresses the operator mixing among different flavors [25] This simplifies the renormalization of the scalar and tensor charges, and allows us to avoid potentially large contamination to the small strange quark contributions from the light quark ones. We exploited this advantage in the previous calculations of σπN for Nf 1⁄4 2 through the Feynman-Hellmann theorem [24] and σs for Nf 1⁄4 2 and 2 þ 1 from nucleon three-point functions [25,26].
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