论文标题
向前光线散射和电磁校正对辐射真空极化
Forward light-by-light scattering and electromagnetic correction to hadronic vacuum polarization
论文作者
论文摘要
晶格QCD计算辐射真空极化（HVP）已经达到了不再忽略电磁校正（E.M.）校正的精度。这种校正在计算上既具有挑战性又难以验证，因为它会导致紫外线（UV）差异和与无质量光子相关的大量红外（IR）效应。 While we precisely determine the UV divergence using the operator-product expansion, we propose to introduce a separation scale $Λ\sim400\;$MeV into the internal photon propagator, whereby the calculation splits into a short-distance part, regulated in the UV by the lattice and in the IR by the scale $Λ$, and a UV-finite long-distance part to be treated with coordinate-space methods,从而完全避免了有限大小的效果。为了预测长距离部分，我们表达了紫外线调节的E.M.通过向前的辐射光（HLBL）散射幅度对HVP进行校正，并通过色散总和规则将后者与$γ^*γ^*$融合横截面相关联。通过从树级$γ^*γ^*^*\ to e^+e^ - $横截面重现了两循环QED真空极化（VP）来测试关系之后，我们预测了预期的lattice-qCD Integrand，由$γ^*γ^*γ^*γ^*γ^*to-to-togument和$ ccd。
Lattice QCD calculations of the hadronic vacuum polarization (HVP) have reached a precision where the electromagnetic (e.m.) correction can no longer be neglected. This correction is both computationally challenging and hard to validate, as it leads to ultraviolet (UV) divergences and to sizeable infrared (IR) effects associated with the massless photon. While we precisely determine the UV divergence using the operator-product expansion, we propose to introduce a separation scale $Λ\sim400\;$MeV into the internal photon propagator, whereby the calculation splits into a short-distance part, regulated in the UV by the lattice and in the IR by the scale $Λ$, and a UV-finite long-distance part to be treated with coordinate-space methods, thereby avoiding power-law finite-size effects altogether. In order to predict the long-distance part, we express the UV-regulated e.m. correction to the HVP via the forward hadronic light-by-light (HLbL) scattering amplitude and relate the latter via a dispersive sum rule to $γ^*γ^*$ fusion cross-sections. Having tested the relation by reproducing the two-loop QED vacuum polarization (VP) from the tree-level $γ^*γ^*\to e^+e^-$ cross-section, we predict the expected lattice-QCD integrand resulting from the $γ^*γ^*\toπ^0$ process.
