Nucleon axial charge from quenched lattice QCD with domain wall fermions and improved gauge action (original) (raw)
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Nucleon axial charge from quenched lattice QCD with domain wall fermions
Physical Review D, 2003
We present a quenched lattice calculation of the nucleon isovector vector and axial-vector charges gV and gA. The chiral symmetry of domain wall fermions makes the calculation of the nucleon axial charge particularly easy since the Ward-Takahashi identity requires the vector and axial-vector currents to have the same renormalization, up to lattice spacing errors of order O(a^2). The DBW2 gauge action provides enhancement of the good chiral symmetry properties of domain wall fermions at larger lattice spacing than the conventional Wilson gauge action. Taking advantage of these methods and performing a high statistics simulation, we find a significant finite volume effect between the nucleon axial charges calculated on lattices with (1.2 fm)^3 and (2.4 fm)^3 volumes (with lattice spacing, a, of about 0.15 fm). On the large volume we find gA = 1.212 +/- 0.027(statistical error) +/- 0.024(normalization error). The quoted systematic error is the dominant (known) one, corresponding to current renormalization. We discuss other possible remaining sources of error. This theoretical first principles calculation, which does not yet include isospin breaking effects, yields a value of gA only a little bit below the experimental one, 1.2670 +/- 0.0030.
An accurate calculation of the nucleon axial charge with lattice QCD
arXiv: High Energy Physics - Lattice, 2017
Author(s): Berkowitz, Evan; Brantley, David; Bouchard, Chris; Chang, Chia Cheng; Clark, MA; Garron, Nicholas; Joo, Balint; Kurth, Thorsten; Monahan, Chris; Monge-Camacho, Henry; Nicholson, Amy; Orginos, Kostas; Rinaldi, Enrico; Vranas, Pavlos; Walker-Loud, Andre | Abstract: We report on a lattice QCD calculation of the nucleon axial charge, gAg_AgA, using M quot;{o}bius Domain-Wall fermions solved on the dynamical Nf=2+1+1N_f=2+1+1Nf=2+1+1 HISQ ensembles after they are smeared using the gradient-flow algorithm. The calculation is performed with three pion masses, mpisim310,220,130m_\pi\sim\{310,220,130\}mpisim310,220,130 MeV. Three lattice spacings ($a\sim\{0.15,0.12,0.09\}$ fm) are used with the heaviest pion mass, while the coarsest two spacings are used on the middle pion mass and only the coarsest spacing is used with the near physical pion mass. On the mpisim220m_\pi\sim220mpisim220 MeV, asim0.12a\sim0.12asim0.12 fm point, a dedicated volume study is performed with mpiLsim3.22,4.29,5.36m_\pi L \sim \{3.22,4.29,5.36\}mpiLsim3.22,4.29,5.36. Using a new strategy motivated by the Feynman-Hellmann ...
Nucleon Axial Charge in (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:mn2mml:mo+mml:mn1)-Flavor Dynamical-Lattice QCD with Domain-Wall Fermions
Physical Review Letters, 2008
We present results for the nucleon axial charge gA at a fixed lattice spacing of 1/a = 1.73(3) GeV using 2+1 flavors of domain wall fermions on size 16 3 × 32 and 24 3 × 64 lattices (L = 1.8 and 2.7 fm) with length 16 in the fifth dimension. The length of the Monte Carlo trajectory at the lightest mπ is 7360 units, including 900 for thermalization. We find finite volume effects are larger than the pion mass dependence at mπ = 330 MeV. We also find that gA exhibits a scaling with the single variable mπL which can also be seen in previous two-flavor domain wall and Wilson fermion calculations. Using this scaling to eliminate the finite-volume effect, we obtain gA = 1.20(6)(4) at the physical pion mass, mπ = 135 MeV, where the first and second errors are statistical and systematic. The observed finite-volume scaling also appears in similar quenched simulations, but disappear when V ≥ (2.4 fm) 3. We argue this is a dynamical quark effect.
Finite-size scaling in nucleon axial charge from 2+1-flavor DWF lattice QCD
Proceedings of The 30th International Symposium on Lattice Field Theory — PoS(Lattice 2012)
We report the current status of the ongoing lattice-QCD calculations of nucleon isovector axial charge, g A , using the RBC/UKQCD 2+1-flavor dynamical domain-wall fermion ensembles at lattice cutoff of about a −1 = 1.4 GeV in a spatial volume (L = 4.6fm) 3. The result from the ensemble with m π = 250 MeV pion mass, corresponding to the finite-size scaling parameter m π L ∼ 5.8, agrees well with an earlier result at a −1 = 1.7 GeV, L = 2.8 fm, and m π = 420 MeV, with similar m π L. This suggests the systematic error from excited-state contamination is small in both ensembles and about 10-% deficit in g A we are observing is likely a finite-size effect that scales with m π L. We also report the result from the lighter, m π = 170 MeV ensemble.
2018
We report on a lattice QCD calculation of the nucleon axial charge, g A , using Möbius Domain-Wall fermions solved on the dynamical N f = 2 + 1 + 1 HISQ ensembles after they are smeared using the gradient-flow algorithm. The calculation is performed with three pion masses, mπ ∼ {310, 220, 130} MeV. Three lattice spacings (a ∼ {0.15, 0.12, 0.09} fm) are used with the heaviest pion mass, while the coarsest two spacings are used on the middle pion mass and only the coarsest spacing is used with the near physical pion mass. On the mπ ∼ 220 MeV a ∼ 0.12 fm point, a dedicated volume study is performed with mπL ∼ {3.22, 4.29, 5.36}. Using a new strategy motivated by the Feynman-Hellmann Theorem, we achieve a precise determination of g A with relatively low statistics, and demonstrable control over the excited state, continuum, infinite volume and chiral extrapolation systematic uncertainties, the latter of which remains the dominant uncertainty. Our final determination at 2.6% total uncertainty is g A = 1.278(21)(26), with the first uncertainty including statistical and systematic uncertainties from fitting and the second including model selection systematics related to the chiral and continuum extrapolation. The largest reduction of the second uncertainty will come from a greater number of pion mass points as well as more precise lattice QCD results near the physical pion mass.
Nucleon Axial Charge in (2+1)Flavor Dynamical-Lattice QCD with Domain-Wall Fermions
Physical Review Letters, 2008
We present results for the nucleon axial charge g_A at a fixed lattice spacing of 1/a=1.73(3) GeV using 2+1 flavors of domain wall fermions on size 16^3x32 and 24^3x64lattices (L=1.8 and 2.7 fm) with length 16 in the fifth dimension. The length of the Monte Carlo trajectory at the lightest m_\pi is 7360 units, including 900 for thermalization. We find finite volume effects are larger than the pion mass dependence at m_\pi= 330 MeV. We also find that g_A exhibits a scaling with the single variable m_\pi L which can also be seen in previous two-flavor domain wall and Wilson fermion calculati ons. Using this scaling to eliminate the finite-volume effect, we obtain g_A = 1.20(6)(4) at the physical pion mass, m_\pi = 135 MeV, where the first and second errors are statistical and systematic. The observed finite-volume scaling also appears in similar quenched simulations, but disappear when V\ge (2.4 fm)^3. We argue this is a dynamical quark effect.
Nucleon structure from lattice QCD with domain wall fermions
Nuclear Physics B - Proceedings Supplements, 2004
We report the current status of RBCK calculations on nucleon structure with both quenched and unquenched lattice &CD. The combination of domain wall fermions and DBW2 gauge action works well for quantities like isovector vector and axial charges, moments of structure functions (ST),, dl, and (l)ap, and nucleon decay matrix elements. Good chiral symmetry is observed, and translates into continuum-like behavior of non-perturabtive renormalization where explicitly checked. Pion form factor calculation in the same framework is also reported.
P oS(LATTICE 2007)162 Nucleon and Nucleon-to- ∆ Axial Form Factors from Lattice QCD
2007
We present results on the nucleon axial vector form factors GA(q2) and Gp(q2) in the quenched theory and using two degenerate flavors of dynamical Wilson fermions for momentum transfer squared from about 0.1 to about 2 GeV2 and for pion masses in the range of 380 to 600 MeV. We also present results on the corresponding N to ∆ axial vector transition form factors CA5 (q2) and CA6 (q2) using, in addition to Wilson fermions, domain wall valence quarks and dynamical staggered sea quarks provided by the MILC collaboration. The XXV International Symposium on Lattice Field Theory
Lattice QCD Study for Confinement and Hadrons
Using SU(3) lattice QCD, we perform the detailed studies of the three-quark and the multi-quark potentials. From the accurate calculation for more than 300 different patterns of 3Q systems, the static ground-state 3Q potential Vrm3Qrmg.s.V_{\rm 3Q}^{\rm g.s.}Vrm3Qrmg.s. is found to be well described by the Coulomb plus Y-type linear potential (Y-Ansatz) within 1%-level deviation. As a clear evidence for Y-Ansatz, Y-type flux-tube formation is actually observed on the lattice in maximally-Abelian projected QCD. For about 100 patterns of 3Q systems, we perform the accurate calculation for the 1st excited-state 3Q potential Vrm3Qrme.s.V_{\rm 3Q}^{\rm e.s.}Vrm3Qrme.s. by diagonalizing the QCD Hamiltonian in the presence of three quarks, and find a large gluonic-excitation energy DeltaErm3QequivVrm3Qrme.s.−Vrm3Qrmg.s.\Delta E_{\rm 3Q} \equiv V_{\rm 3Q}^{\rm e.s.}-V_{\rm 3Q}^{\rm g.s.}DeltaErm3QequivVrm3Qrme.s.−Vrm3Qrmg.s. of about 1 GeV, which gives a physical reason of the success of the quark model. DeltaErm3Q\Delta E_{\rm 3Q}DeltaErm3Q is found to be reproduced by the ``inverse Mercedes Ansatz'', which ind...