arXiv 2003.139202020-03hep-ph

手征奇扭3部分子分布e（x）的奇异性

On the Singular Behavior of the Chirality-Odd Twist-3 Parton Distribution e(x)

J. P. Ma, G. P. Zhang

备注：: Published version
发表信息：: Phys. Lett. B811 (2020) 135947
DOI：: 10.1016/j.physletb.2020.135947

摘要：

手征奇扭3部分子分布$e(x)$的第一阶矩与π-核子$σ$项有关，后者对唯象学很重要.然而，在分布中可能存在与$δ(x)$成比例的奇异贡献，这阻止了从实验中用$e(x)$确定$σ$项。有两种方法来证明存在。第一种是基于操作员身份。第二种是基于有限质量单夸克态的微扰计算。我们表明，所有的贡献成比例的$δ(x)$在第一种方法中，实际上被取消。对于第二种方法，我们发现含无质量夸克的多部分子态的$e(x)$对$δ(x)$没有贡献。考虑到质子本质上是一个多部分子态，从微扰理论的角度出发，我们认为轻夸克质量会抑制$δ(x)$贡献的影响。详细讨论了$e(x)$的切割图和未切割图之间的差异。

英文摘要：

The first moment the chirality-odd twist-3 parton distribution $e(x)$ is related to the pion-nucleon $σ$-term which is important for phenomenology. However, the possible existence of a singular contribution proportional to $δ(x)$ in the distribution prevents from the determination of the $σ$-term with $e(x)$ from experiment. There are two approaches to show the existence. The first one is based on an operator identity. The second one is based on a perturbative calculation of a single quark state with finite quark mass. We show that all contributions proportional to $δ(x)$ in the first approach are in fact cancelled. To the second approach we find that $e(x)$ of a multi-parton state with a massless quark has no contribution with $δ(x)$. Considering that a proton is essentially a multi-parton state, the effect of the contribution with $δ(x)$ is expected to be suppressed by light quark masses with arguments from perturbation theory. A detailed discussion about the difference between cut- and uncut diagrams of $e(x)$ is provided.

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摘要：

英文摘要：

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