Nucleon axial charge from quenched lattice QCD with domain wall fermions and improved gauge action

Sasaki, Shoichi; Blum, Tom; Ohta, Shigemi; Orginos, Konstantinos

doi:10.1016/s0920-5632(01)01695-4

Cited by 15 publications

(12 citation statements)

References 7 publications

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“…This result leaves open the question of why present lattice calculations substantially underpredict g A . Recent lattice results do suggest large finite volume effects [2]. This does not contradict the present result.…”

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confidence: 75%

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The extraction of gA from finite volume systems: the long and short of it

Cohen¹

2002

Physics Letters B

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Due to a pion-pole contribution, the nucleon axial current matrix elements can be visualized in position space as becoming delocalized as the chiral limit is approached, with one-third of the current at distance of order 1/mπ. However, this delocalization effect will not cause calculations of gA in a finite system with standard boundary conditions (periodic for boson fields, antiperiodic for fermions) to have large finite volume effects. This is seen by calculating gA using a nonstandard current with axial quantum numbers. The matrix elements of this new current lacks a pion pole and is not delocalized; however, its zero-momentum matrix element is identical to that of the standard axial current both for infinite and finite volumes.

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supporting

confidence: 75%

“…Attempts to calculate g A in lattice QCD have given values which are well below the experimental value [1]. It has recently been argued that this failure may be due to very large finite volume effects [2]. One may ask whether there is a basis for understanding the emergence of large finite volume effects from the structure of QCD.…”

mentioning

confidence: 99%

The extraction of gA from finite volume systems: the long and short of it

Cohen¹

2002

Physics Letters B

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“…Perhaps the most famous example is the axial charge of the nucleon where early simulations revealed a striking decrease of g A as the pion mass decreased -in the opposite direction from the experimental data [6][7][8]. We shall see that our simple chiral model is able to reproduce this feature.…”

Section: Introductionmentioning

confidence: 70%

“…(4), (6) and (7) are dependent on the parameters Ω, R, L, m q and m π but also on the unknown values f (R) and g(R) ≡ g 0 , which are given by…”

Section: The Linear Boundary Conditionmentioning

confidence: 99%

Finite volume dependence of hadron properties and lattice QCD

Thomas

Ashley

Leinweber

et al. 2005

J. Phys.: Conf. Ser.

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Abstract. Because the time needed for a simulation in lattice QCD varies at a rate exceeding the fourth power of the lattice size, it is important to understand how small one can make a lattice without altering the physics beyond recognition. It is common to use a rule of thumb that the pion mass times the lattice size should be greater than (ideally much greater than) four (i.e., mπL ≫ 4). By considering a relatively simple chiral quark model we are led to suggest that a more realistic constraint would be mπ(L − 2R) ≫ 4, where R is the radius of the confinement region, which for these purposes could be taken to be around 0.8-1.0 fm. Within the model we demonstrate that violating the second condition can lead to unphysical behaviour of hadronic properties as a function of pion mass. In particular, the axial charge of the nucleon is found to decrease quite rapidly as the chiral limit is approached. IntroductionOur current capacity to compute hadron properties in lattice QCD is constrained by the need to take many limits. For example, we need to take the spacing a → 0, the size of the lattice L → ∞ and the quark mass to around 5 MeV. Of course, these limits are not unconnected because the size of a region of space big enough to contain (say) a proton will need to grow with the Compton wavelength of the pion. At present, with lattice spacings that represent a reasonable approximation to the continuum limit and for full QCD with reasonable chiral symmetry, the time for a lattice simulation scales roughly like m −9 π and we are limited to pion masses larger than 0.4-0.5 GeV. This has led to much effort to explore the application of chiral perturbation theory as a tool for extrapolating hadron properties to the physical pion mass [1][2][3].In such an environment there is great interest in seeing whether one can lower the pion mass without increasing the size of the lattice, thereby saving a factor of m 4 π . Indeed, there have been many calculations for which even the rather optimistic rule of thumb that m π L > 4 has not been satisfied. Considerable attention has been devoted to studying such systems within the framework of effective field theory in order to understand how the relevant path integral might change as we go from one regime to another [4,5].The question we ask is somewhat different. We consider a simple chiral quark model upon which we impose boundary conditions which roughly approximate those on a lattice. Simple inspection of the solutions naturally leads one to conclude that the condition noted above is incorrect. Indeed, the pion cloud of the nucleon does not even begin until one is outside the region of space in which the valence quarks are confined. Within the bag model this is characterised by the bag radius, R, and within the cloudy bag model as well as the model

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“…We use the DBW2 gauge action which is known to improve the domain wall fermion chiral properties [36,37]. We have 416 lattices of size 16 3 × 32 at β = 0.870 with lattice spacing a −1 = 1.3GeV, providing us with a physical volume (∼ (2.4 f m) 3 ) large enough to reduce finite size effects known to affect some nucleon matrix elements, such as g A [38,39]. Using fifth dimension length L s = 16 we achieve a residual mass m res ∼ 0.8MeV [36,37].…”

Section: Lattice Resultsmentioning

confidence: 99%

Spin on the Lattice

Orginos

2003

AIP Conference Proceedings

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I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed.Understanding the basic properties of matter requires the understanding of the nucleon structure. Quantum Chromodynamics (QCD) is the theory describing strong interactions and hence is responsible for the properties of the nuclear matter. Although QCD has been around for more than twenty years, its non-perturbative nature is an obstacle to the direct connection of low energy physics to quarks and gluons, the fundamental degrees of freedom of the theory. Unlike QED, non-perturbative techniques had to be developed in order to understand the QCD predictions at low energies. The lattice formulation of QCD is both a non-perturbative way to define the theory and a very powerful tool in understanding its properties.Deep inelastic scattering of leptons on nucleons has been an important tool in understanding the structure of hadrons. Over the last few decades experiments at SLAC, Fermilab, CERN, DESY, and more recently at RHIC and JLAB, have measured the quark and gluon light cone distribution functions of the nucleon. These experiments have substantially advanced our knowledge of the properties of hadrons. However, we would also like to study how this observed rich phenomenology arises form first principles, i.e. QCD. With todays advances in computer technology, algorithms, and recent developments in lattice regularization of fermions, lattice calculations can complement the experimental effort and promote our understanding of the non-perturbative nature of QCD.

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Nucleon axial charge from quenched lattice QCD with domain wall fermions and improved gauge action

Cited by 15 publications

References 7 publications

The extraction of gA from finite volume systems: the long and short of it

The extraction of gA from finite volume systems: the long and short of it

Finite volume dependence of hadron properties and lattice QCD

Spin on the Lattice

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