Nucleon matrix elements using the variational method in lattice QCD

Dragos, Jack; Horsley, R.; Kamleh, Waseem; Leinweber, Derek B.; Nakamura, Y.; Rakow, P. E. L.; Schierholz, G.; Young, R.; Zanotti, J. M.

doi:10.1103/physrevd.94.074505

Cited by 36 publications

(47 citation statements)

References 33 publications

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“…Both the PEVA and conventional variational analysis show clear and clean plateaus in G E (Q 2 ) with good excited state control. This supports previous work demonstrating the utility of variational analysis techniques in calculating baryon matrix elements [21,22]. By using such techniques we are able to cleanly isolate precise values for the Sachs electric form factor of the ground-state proton and neutron.…”

Section: Worksupporting

confidence: 87%

Opposite-parity contaminations in lattice nucleon form factors

2019

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The recently-introduced Parity Expanded Variational Analysis (PEVA) technique allows for the isolation of baryon eigenstates at finite momentum free from opposite-parity contamination. In this paper, we establish the formalism for computing form factors of spin-1 /2 states using PEVA. Selecting the vector current, we compare the electromagnetic form factors of the ground state nucleon extracted via this technique to a conventional parity-projection approach. Our results show a statistically significant discrepancy between the PEVA and conventional analyses. This indicates that existing calculations of matrix elements of ground state baryons at finite momentum can be affected by systematic errors of ∼ 20 % at physical quark masses. The formalism introduced here provides an effective approach to removing these systematic errors.

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Section: Worksupporting

confidence: 87%

Opposite-parity contaminations in lattice nucleon form factors

2019

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“…We also calculate the tensor coupling, g T = 1 δq , and scalar coupling, g S , the same way. We used a conventional measurement strategy for the former with seven source-sink pairs for each configuration, and an "all-mode-averaging (AMA)" strategy [31] for the latter with 112 sloppy solves with sources at two sets of 8 evenly spaced spatial locations, from (0,0,0) to (16,16,16) and from (8,8,8) to (24,24,24) for T = 0, 8,16,24,32,40, and 48 and four precise solves at spatial origins with T = 0, 16, 32 and 48 for each configuration. In addition, to test for excited state contamination, calculations with source-sink separation of 7 lattice units were made with 64 sloppy solves with sources at 8 evenly spaced spatial locations with T = 0, 8, 16, 24, 32, 40, 48, and 56 and and one precise solve at spatial originswith T = 0.…”

Section: Methodsmentioning

confidence: 99%

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

et al. 2020

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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.

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“…Variational approaches have been used to study nucleon structure in Refs. [5][6][7][8][9], which used bases of interpolators with different smearing widths and different site-local spin structures, and Ref. [10], which used the distillation method to enable the use of interpolators with a variety of local structures including covariant derivatives.…”

Section: Introductionmentioning

confidence: 99%

Excited-state effects in nucleon structure on the lattice using hybrid interpolators

et al. 2019

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It would be very useful to find a way of reducing excited-state effects in lattice QCD calculations of nucleon structure that has a low computational cost. We explore the use of hybrid interpolators, which contain a nontrivial gluonic excitation, in a variational basis together with the standard interpolator with tuned smearing width. Using the clover discretization of the field strength tensor, a calculation using a fixed linear combination of standard and hybrid interpolators can be done using the same number of quark propagators as a standard calculation, making this a cost-effective option. We find that such an interpolator, optimized by solving a generalized eigenvalue problem, reduces excited-state contributions in two-point correlators. However, the effect in three-point correlators, which are needed for computing nucleon matrix elements, is mixed: for some matrix elements such as the tensor charge, excited-state effects are suppressed, whereas for others such as the axial charge, they are enhanced. The results illustrate that the variational method is not guaranteed to reduce the net contribution from excited states except in its asymptotic regime, and suggest that it may be important to use a large basis of interpolators capable of isolating all of the relevant low-lying states. * jeremy.green@desy.de 1 The comparison is more difficult when using the distillation method, which uses timeslice sources rather than the point sources used in standard calculations. 2 The resulting basis of interpolators is similar to the one called B 3 in Ref. [10].

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Nucleon matrix elements using the variational method in lattice QCD

Cited by 36 publications

References 33 publications

Opposite-parity contaminations in lattice nucleon form factors

Opposite-parity contaminations in lattice nucleon form factors

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

Excited-state effects in nucleon structure on the lattice using hybrid interpolators

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