Lattice Computation of the Nucleon Scalar Quark Contents at the Physical Point

We present a QCD calculation of the u, d, and s scalar quark contents of nucleons based on 47 lattice ensembles with Nf=2+1 dynamical sea quarks, 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm, and pion masses down to 120 MeV. Using the Feynman-Hellmann theorem, we obtain fNud=0.0405(40)(35) and fNs=0.113(45)(40), which translates into σπN=38(3)(3)  MeV, σsN=105(41)(37)  MeV, and yN=0.20(8)(8) for the sigma terms and the related ratio, where the first errors are statistical and the second errors are systematic. Using isospin relations, we also compute the individual up and down quark contents of the proton and neutron (results in the main text)

A lattice study of the nucleon quark content at the physical point

After a detailed analysis of possible sources of systematic uncertainty, ab-initio N f = 2 + 1 results for the up-down and strange quark content - with pion masses all the way down to the physical point - are presented and discussed

High precision scale setting on the lattice

International audienc

Leading hadronic contribution to the muon magnetic moment from lattice QCD

International audienceThe standard model of particle physics describes the vast majority of experiments and observations involving elementary particles. Any deviation from its predictions would be a sign of new, fundamental physics. One long-standing discrepancy concerns the anomalous magnetic moment of the muon, a measure of the magnetic field surrounding that particle. Standard-model predictions1 exhibit disagreement with measurements2 that is tightly scattered around 3.7 standard deviations. Today, theoretical and measurement errors are comparable; however, ongoing and planned experiments aim to reduce the measurement error by a factor of four. Theoretically, the dominant source of error is the leading-order hadronic vacuum polarization (LO-HVP) contribution. For the upcoming measurements, it is essential to evaluate the prediction for this contribution with independent methods and to reduce its uncertainties. The most precise, model-independent determinations so far rely on dispersive techniques, combined with measurements of the cross-section of electron–positron annihilation into hadrons3,4,5,6. To eliminate our reliance on these experiments, here we use ab initio quantum chromodynamics (QCD) and quantum electrodynamics simulations to compute the LO-HVP contribution. We reach sufficient precision to discriminate between the measurement of the anomalous magnetic moment of the muon and the predictions of dispersive methods. Our result favours the experimentally measured value over those obtained using the dispersion relation. Moreover, the methods used and developed in this work will enable further increased precision as more powerful computers become available