非对角DVCS与无自旋核子到两核子过渡γ* π→γππ
Non-diagonal DVCS with spinless hadron-to-two-hadron transition $γ^* π\to γππ$
AI总结：
本文提出了一种无自旋核子到两核子过渡的GPDs形式，通过角分布和Omnès表示法构建了现象学模型，用于研究γ* π→γππ过程。
摘要：
我们提出了适用于无自旋核子情况的核子到两核子过渡广义部分子分布（GPDs）的公式。引入了无自旋核子的扭-2无极化和极化π→ππ过渡GPDs的定义，并特别选择了刻画产生两个π子系统的动量变量。在ρ(770)附近，我们推导了e⁻π→e⁻γππ截面的两π衰变角分布，结合了Bethe-Heitler和深层虚拟康普顿散射过程。每个截面都表现出独特的角分布，这对其产生的ρ(770)共振的极化状态敏感。此外，我们构建了π→ππ过渡GPDs的双部分波展开，作为从π到自旋-ℓ共振态过渡的GPDs的一般化。借助Omnès表示法，我们利用低能ππ散射相移约束π→ππ过渡GPDs，并建立了这些GPDs的现象学模型。
英文摘要：
We present the formalism of hadron-to-two-hadron transition generalized parton distributions (GPDs) for spinless hadron case. Definitions of the twist-2 unpolarized and polarized $π\toππ$ transition GPDs are introduced with a particular choice of kinematic variables that characterize the produced two-pion system. In the vicinity of $ρ(770)$, we work out the two-pion decay angular distributions of the $e^-π\to e^-γππ$ cross section, incorporating both the Bethe-Heitler and deeply virtual Compton scattering processes. Each cross section exhibits a distinctive angular distribution, which is sensitive to the polarization states of the produced $ρ(770)$ resonance. In addition, we construct the double partial-wave expansion of $π\toππ$ transition GPDs in the two-pion decay angles as a generalization of GPDs for transition from a pion to a spin-$\ell$ resonance state. With the help of the Omnès representation, we constrain the $π\toππ$ transition GPDs in terms of the low energy $ππ$ scattering phase shift and build a phenomenological model for these GPDs.
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