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arXiv 0710.0422hep-lat
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N_f=2+1动力学畴壁费米子的核子形状因子和结构函数

Nucleon form factors and structure functions with N_f=2+1 dynamical domain wall fermions

UKQCD Collaboration, Takeshi Yamazaki, Shigemi Ohta

备注：
14 pages, Presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, Germany
发表信息：
PoSLAT2007:165,2007
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摘要：

利用RIKEN-BNL-Columbia（RBC）和UKQCD合作组的计算结果，报道了在数值格点量子色动力学（QCD）中核子的等矢量形状因子和结构函数的低阶矩.我们计算了具有四个轻夸克质量的矩阵元，对应的π介子质量值为m_π= 330-670 MeV，而动力学奇异质量固定在一个接近物理的值，在（2.7 fm）^3空间体积上。我们发现，我们的轴向电荷，g_A，在最轻的质量表现出较大的偏差，从较重的质量的结果。这种偏离似乎是一种有限尺寸效应，因为g_A值与一个参数m_πL成比例，m_πL是π介子质量和线性空间晶格尺寸的乘积。在早期的2味动力学夸克和威尔逊夸克计算中也可以看到这种标度。没有这个最轻点，三个较重质量的结果只显示出非常轻微的质量依赖性，并线性外推到g_A=1.16（6）。我们确定了四个形状因子，矢量（狄拉克），诱导张量（泡利），轴矢量和诱导赝标量，在一些有限的动量转移值以及。在物理π质量下，由形状因子的动量转移依赖关系确定的形状因子均方根半径比相应的实验结果小20-30%。等矢量夸克动量与螺旋度之比< x>_{u-d}/< x>_{Δu - Δd}与实验结果一致，但没有太大的质量依赖性，包括最轻点。我们通过常数拟合得到估计值0.81（2）。虽然个别的动量和螺旋度分数尚未重整化，但它们显示出令人鼓舞的实验趋势。

英文摘要：

We report isovector form factors and low moments of structure functions of nucleon in numerical lattice quantum chromodynamics (QCD) from the on-going calculations by the RIKEN-BNL-Columbia (RBC) and UKQCD Collaborations with (2+1) dynamical flavors of domain-wall fermion (DWF) quarks. We calculate the matrix elements with four light quark masses, corresponding to pion mass values of m_π= 330-670 MeV, while the dynamical strange mass is fixed at a value close to physical, on (2.7 fm)^3 spatial volume. We found that our axial charge, g_A, at the lightest mass exhibits a large deviation from the heavier mass results. This deviation seems to be a finite-size effect as the g_A value scales with a single parameter, m_πL, the product of pion mass and linear spatial lattice size. The scaling is also seen in earlier 2-flavor dynamical DWF and Wilson quark calculations. Without this lightest point, the three heavier mass results show only very mild mass dependence and linearly extrapolate to g_A=1.16(6). We determined the four form factors, the vector (Dirac), induced tensor (Pauli), axial vector and induced pseudoscalar, at a few finite momentum transfer values as well. At the physical pion mass the form-factors root mean square radii determined from the momentum-transfer dependence %of the form factors are 20-30% smaller than the corresonding experiments. The ratio of the isovector quark momentum to helicity fractions, < x>_{u-d}/< x>_{Δu - Δd} is in agreement with experiment without much mass dependence including the lightest point. We obtain an estimate, 0.81(2), by a constant fit. Although the individual momentum and helicity fractions are yet to be renormalized, they show encouraging trend toward experiment.

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