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arXiv 1306.2916hep-lathep-ph
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用格点量子色动力学和NNLO手征微扰理论计算π介子矢量形状因子

The pion vector form factor from lattice QCD and NNLO chiral perturbation theory

Bastian B. Brandt, Andreas Juttner, Hartmut Wittig

摘要:

本文在格点量子色动力学中,采用两个O(a)改进的Wilson夸克,在0.05-0.08fm的三种不同格点间距范围内,计算了π介子的电磁形状因子、衰变常数和质量,π介子质量在280 - 630 MeV之间,m_piL>~ 4.使用部分扭曲的边界条件和随机估计,我们获得了一组密集的精确的数据点的形状因子在非常小的动量转移,允许独立于模型的提取的电荷半径。手征微扰理论(ChPT)增加的条款模型晶格文物,然后比较的数据。在次领先阶有效理论未能产生一个完整的π观测值的一致的描述,但描述的数据时,只考虑衰变常数和质量。相比之下,使用下一个到下一个到前导顺序表达式来执行全局拟合会导致对所有数据的一致描述。我们得到<r^2_pi>=0.481(33)(13)fm^2,这是物理点处电荷半径的最终结果。计算还得到了手征极限下π介子衰变常数F_pi/F=1.080(16)(6),夸克凝聚体σ ^{13}_MSbar(2GeV)=261(13)(1)MeV和SU(2)ChPT的几个低能常数的估计值。

英文摘要:

We present a comprehensive study of the electromagnetic form factor, the decay constant and the mass of the pion computed in lattice QCD with two degenerate O(a)-improved Wilson quarks at three different lattice spacings in the range 0.05-0.08fm and pion masses between 280 and 630MeV at m_pi L >~ 4. Using partially twisted boundary conditions and stochastic estimators, we obtain a dense set of precise data points for the form factor at very small momentum transfers, allowing for a model-independent extraction of the charge radius. Chiral Perturbation Theory (ChPT) augmented by terms which model lattice artefacts is then compared to the data. At next-to-leading order the effective theory fails to produce a consistent description of the full set of pion observables but describes the data well when only the decay constant and mass are considered. By contrast, using the next-to-next-to-leading order expressions to perform global fits result in a consistent description of all data. We obtain <r^2_pi>=0.481(33)(13)fm^2 as our final result for the charge radius at the physical point. Our calculation also yields estimates for the pion decay constant in the chiral limit, F_pi/F=1.080(16)(6), the quark condensate, Sigma^{1/3}_MSbar(2GeV)=261(13)(1)MeV and several low-energy constants of SU(2) ChPT.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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