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arXiv 0709.1745hep-ph
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从瞬子真空看π介子和K介子的电磁形状因子

Electromagnetic form factors of the pion and kaon from the instanton vacuum

Seung-il Nam, Hyun-Chul Kim

摘要:

基于大N_c极限下瞬子真空的规范低能有效手征作用,我们研究了类空区域Q^2 ~< 1 GeV中的π介子和K ~+(pi^+,K^+,K^0)电磁形状因子。考虑了SU(3)对称性破缺的显式味。结果表明,非局部贡献对于再现实验数据至关重要。虽然π介子电磁形状因子与数据吻合良好,但K介子似乎被低估了。我们还计算了π介子和K介子的电磁荷半径:<r^2>_{pi^+}=0.455 fm^2,<r^2>_{K^+}=0.486 fm^2和<r^2>_{K^0}=-0.055 fm^2,除了平均瞬子尺寸和瞬子间距离外,没有任何可调的自由参数,它们与实验数据是一致的。由π电荷半径估算出大N_c极限下的低能常数L_9为8.42*10^{-3}。

英文摘要:

We investigate the pion and kaon (pi^+, K^+, K^0) electromagnetic form factors in the space-like region: Q^2 ~< 1 GeV, based on the gauged low-energy effective chiral action from the instanton vacuum in the large N_c limit. Explicit flavor SU(3) symmetry breaking is taken into account. The nonlocal contributions turn out to be crucial to reproduce the experimental data. While the pion electromagnetic form factor is in good agreement with the data, the kaon one seems underestimated. We also calculate the electromagnetic charge radii for the pion and kaon: <r^2>_{pi^+}=0.455 fm^2, <r^2>_{K^+}=0.486 fm^2 and <r^2>_{K^0}=-0.055 fm^2 without any adjustable free parameter except for the average instanton size and inter-instanton distance, and they are compatible with the experimental data. The low-energy constant L_9 in the large N_c limit is estimated to be 8.42*10^{-3} from the pion charge radius.

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