Nucleon mass and isovector couplings in 2+1 -flavor dynamical domain-wall lattice QCD near physical mass

Abstract

We report nucleon mass, isovector vector and axial-vector charges, and tensor and scalar couplings, calculated using two recent 2+1-flavor dynamical domain-wall fermions lattice-QCD ensembles generated jointly by the RIKEN-BNL-Columbia and UKQCD collaborations. These ensembles were generated with Iwasaki × dislocation-suppressing-determinant-ratio gauge action at inverse lattice spacing of 1.378 (7) GeV and pion mass values of 249.4(3) and 172.3(3) MeV. The nucleon mass extrapolates to a value mN = 0.950(5) GeV at physical point. The isovector vector charge renormalizes to unity in the chiral limit, narrowly constraining excited-state contamination in the calculation. The ratio of the isovector axial-vector to vector charges shows a deficit of about ten percent. The tensor coupling no longer depends on mass and extrapolates to 1.04(5) in MS 2-GeV renormalization at physical point, in a good agreement with the value obtained at the lightest mass in our previous calculations and other calculations that followed. The scalar charge, though noisier, does not show mass dependence and is in agreement with other calculations.

Isovector nucleon form factors from 2+1-flavor dynamical domain-wall lattice QCD at the physical mass

“…Statistical significance of these results ranges dependent on renormalizations used for the axialvector current [23,24,35]: From about three standard deviations with the renormalization obtained in the meson-sector calculation to about five standard deviations with the renormalization using the nucleon vector charge. We note the corresponding vector charge calculation suggests possible contamination from nearby excited states [23,24,[35][36][37], in contrast to earlier DWF calculations that did not find any evidence for such contamination [25,35].…”

“…We have been working at physical mass for a while [9,10]. We have used some of these DWF ensembles for studying nucleon [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. We found a deficit [11] in calculated isovector axial charge, , in comparison with its experimental value [26].…”

Nucleon isovector form factors from physical-mass 2+1-flavor dynamical domain-wall QCD

“…As the corresponding vector charge calculation suggests possible contamination from near by excited states [23,24], in contrast to earlier DWF calculations that did not find any evidence for such contamination [25], the form factor calculations presented here can shed some light on this possible contamination from excited states [35,36]. The results presented here were calculated using the "48I" 48 3 × 96 2+1-flavor dynamical Möbius DWF ensemble at physical mass with Iwasaki gauge action of gauge coupling, 𝛽 = 2.13, or of lattice cut off of 𝑎 −1 = 1.730(4) GeV, jointly generated by the RBC and UKQCD Collaborations [9].…”

“…We have used some of these DWF ensembles for studying nucleon [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. We found deficit [11] in calculated isovector axial charge, 𝑔 𝐴 , in comparison with its experimental value [26].…”

Neutrino Oscillation and Lattice QCD

“…These results are all in good agreement with each other, demonstrating the consistency of the LQCD extrapolations. The scatter points (LHP+RBC+UKQCD [26], PACS 22 (128 4 ) [27], PACS 22 (160 4 ) [28], PACS 21 [29,30], and CalLat 21 [31]) denote single-ensemble results. Although these results could have unquantified systematic biases, the results are all still in agreement with each other and with the fully extrapolated results, suggesting that the unknown systematics are likely to be small.…”