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arXiv 1407.4059hep-lathep-phnucl-th
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零动量下形状因子提取的有限体积效应

Finite Volume Effects on the Extraction of Form Factors at Zero Momentum

Brian C. Tiburzi

摘要:

依赖于动量的强子矩阵元是许多唯象学应用所必需的。由于对周期性动量模的限制,在格点量子色动力学计算中,探测低动量区常常是个问题。最近提出了一种新的方法来计算零动量的矩阵元素,否则矩阵元素的直接评估将产生消失的结果。我们澄清了这种方法的假设,从而建立了理论框架,以解决相关的有限体积效应。以π介子电磁形状因子为例,给出了零动量转移时电荷半径和两个高阶矩的计算方法,并确定了相应的有限体积效应。这些计算使用手征微扰理论来解释修正的红外物理,并可以推广到确定有限体积效应的其他强子矩阵元提取零动量。

英文摘要:

Hadronic matrix elements that depend on momentum are required for numerous phenomenological applications. Probing the low-momentum regime is often problematic for lattice QCD computations on account of the restriction to periodic momentum modes. Recently a novel method has been proposed to compute matrix elements at zero momentum, for which straightforward evaluation of the matrix elements would otherwise yield a vanishing result. We clarify an assumption underlying this method, and thereby establish the theoretical framework required to address the associated finite volume effects. Using the pion electromagnetic form factor as an example, we show how the charge radius and two higher moments can be calculated at zero momentum transfer, and determine the corresponding finite volume effects. These computations are performed using chiral perturbation theory to account for modified infrared physics, and can be generalized to ascertain finite volume effects for other hadronic matrix elements extracted at zero momentum.

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