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arXiv 1011.1302hep-lathep-phnucl-th
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2味手征微扰理论中超子的轴向和电磁可观测量

Axial and electromagnetic observables of hyperons in 2-flavor chiral perturbation theory

F. -J. Jiang, B. C. Tiburzi, A. Walker-Loud

备注：
7 pages, talk given at the XXVIII International Symposium on Lattice Filed Theory, June 14-19,2010, Villasimius, Sardinia Italy
发表信息：
PoS Lattice2010:086,2010
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摘要：

双味手征展开为研究强子性质提供了一个有用的微扰框架。这样的展开应表现出显着的改进，超过传统的三味手性展开。虽然原则上可以为各种超子多重态制定双味理论，但K介子阈值的接近会严重破坏这种双味理论在实践中的有效性。我们研究了虚K介子阈值对超子性质的重要性，特别是它们的等矢量轴向电荷和电磁可观测量。特别是，我们揭示了潜在的膨胀参数的虚拟K介子阈值的描述。对于自旋半超子，这个膨胀参数是在理论控制之下的。因此，在双味理论中，虚K介子的贡献可以用π质量平方的解析项来描述。然而，对于自旋为3.5的超子，它更接近于K介子的产生阈值，膨胀参数也没有那么小。击穿$SU(2)$手征微扰理论所示，产生于一个极点的扩展参数与K介子阈值。我们发现，尽管需要对展开参数进行高阶修正来确定自旋三分之二超子的双味理论是否仍然是微扰的，但对于自旋半超子和自旋三分之二超子的等矢量轴向荷和磁矩都存在有用的微扰展开。

英文摘要：

Two-flavor chiral expansions provide a useful perturbative framework to study hadron properties. Such expansions should exhibit marked improvement over the conventional three-flavor chiral expansion. Although in principle one can formulate two-flavor theories for the various hyperon multiplets, the nearness of kaon thresholds can seriously undermine the effectiveness of such two-flavor theories in practice. We investigate the importance of virtual kaon thresholds on hyperon properties, specifically their isovector axial charges and electromagnetic observables. In particular we uncover the underlying expansion parameter governing the description of virtual kaon thresholds. For spin-half hyperons, this expansion parameter is under theoretical control. As a result, the virtual kaon contributions are well described in the two-flavor theory by terms analytic in the pion mass-squared. For spin three-half hyperons, however, one is closer to the kaon production threshold, and the expansion parameter is not as small. Breakdown of $SU(2)$ chiral perturbation theory is shown to arise from a pole in the expansion parameter associated with the kaon threshold. We find that, despite the fact that higher-order corrections to the expansion parameter is necessary to ascertain whether the two-flavor theory of spin three-half hyperons remains perturbative, there is a useful perturbative expansion for isovector axial charges and magnetic moments of both spin-half and spin three-half hyperons.

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