手征微扰理论中核子的前向双虚Compton散射：非极化结构函数的减函数和矩
Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: the subtraction function and moments of unpolarized structure functions
摘要：
核子的前向双虚康普顿散射（Vapor）包含了丰富的核子结构信息，与原子光谱和电子散射中双光子交换效应的计算有关。本文报道了用手征微扰理论（$χ$ PT）对低能电子的准首阶（NLO）计算。在这里，我们专注于非极化VEGF-A振幅$T_1(ν, Q^2)$和$T_2(ν, Q^2)$，以及相应的结构函数$F_1(x, Q^2)$和$F_2(x,Q^2)$。我们的研究结果面临的，在可能的情况下，与“数据驱动”的低能量结构量，如核子极化率的色散评估。我们发现在非常低的动量转移$Q$的色散评估显着的分歧，例如，在零动量转移的极化率的斜率。通过将结果推广到核子质量的倒数的幂，我们再现了已知的“重子”表达式。这是对我们的计算的一个检验，同时也说明了明显的洛伦兹不变（B $χ$ PT）和重子（HB $χ$ PT）框架之间的区别。
英文摘要：
The forward doubly-virtual Compton scattering (VVCS) off the nucleon contains a wealth of information on nucleon structure, relevant to the calculation of the two-photon-exchange effects in atomic spectroscopy and electron scattering. We report on a complete next-to-leading-order (NLO) calculation of low-energy VVCS in chiral perturbation theory ($χ$PT). Here we focus on the unpolarized VVCS amplitudes $T_1(ν, Q^2)$ and $T_2(ν, Q^2)$, and the corresponding structure functions $F_1(x, Q^2)$ and $F_2(x,Q^2)$. Our results are confronted, where possible, with "data-driven" dispersive evaluations of low-energy structure quantities, such as nucleon polarizabilities. We find significant disagreements with dispersive evaluations at very low momentum-transfer $Q$; for example, in the slope of polarizabilities at zero momentum-transfer. By expanding the results in powers of the inverse nucleon mass, we reproduce the known "heavy-baryon" expressions. This serves as a check of our calculation, as well as demonstrates the differences between the manifestly Lorentz-invariant (B$χ$PT) and heavy-baryon (HB$χ$PT) frameworks.
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