Nucleon axial, tensor, and scalar charges and σ -terms in lattice QCD

Abstract

We determine the nucleon axial, scalar and tensor charges within lattice quantum chromodynamics including all contributions from valence and sea quarks. We analyze three gauge ensembles simulated within the twisted mass formulation at approximately physical value of the pion mass. Two of these ensembles are simulated with two dynamical light quarks and lattice spacing a ¼ 0.094 fm and the third with a ¼ 0.08 fm includes in addition the strange and charm quarks in the sea. After comparing the results among these three ensembles, we quote as final values our most accurate analysis using the latter ensemble. For the nucleon isovector axial charge we find 1.286(23) in agreement with the experimental value. We provide the flavor decomposition of the intrinsic spin 1 2 ΔΣ q carried by quarks in the nucleon obtaining for the up, down, strange and charm quarks 1 2 ΔΣ u ¼ 0.431ð8Þ, 1 2 ΔΣ d ¼ −0.212ð8Þ, 1 2 ΔΣ s ¼ −0.023ð4Þ and 1 2 ΔΣ c ¼ −0.005ð2Þ, respectively. The corresponding values of the tensor and scalar charges for each quark flavor are also evaluated providing valuable input for experimental searches for beyond the standard model physics. In addition, we extract the nucleon σ-terms and find for the light quark content σ πN ¼ 41.6ð3.8Þ MeV and for the strange σ s ¼ 45.6ð6.2Þ MeV. The y-parameter that is used in phenomenological studies we find y ¼ 0.078ð7Þ.

First moments of the nucleon transverse quark spin densities using lattice QCD

“…Although the central value is lower from our current determination, its error is large, leading to about two standard deviations effect. Furthermore, our determination is fully compatible with the recent FLAG report [43] and with our previous value [44] obtained using only the cB211.072.64 ensemble, which is at the coarsest lattice spacing. B 20 (0)/3 FIG.…”

Thermal WIMPs and the scale of new physics: global fits of Dirac dark matter effective field theories

“…where the upper (lower) sign is for the proton (neutron). We use a rather conservative estimate σ π N = (50 ± 15) MeV [101] that covers the spread between the lattice QCD [111][112][113][114][115][116][117][118] and pionic atom determinations [113,114,117,[119][120][121][122][123]. The other two parameters are ξ [103].…”

Proton mass decomposition: naturalness and interpretations

“…• One can no longer isolate the quark mass contribution to the proton mass, which is scale invariant and has been studied for many decades in chiral perturbation theory [43]. It can also be measured through experiments and calculable through lattice QCD [15,44].…”

“…The heavy quark contribution to the proton mass has been computed on lattice, particularly for the charm quark [44,46]. The nominal contribution is large: P |m c cc|P is on the order of 100 MeV.…”