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arXiv 0811.0266hep-phnucl-exnucl-th
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双光子交换的微扰QCD预言

Perturbative QCD predictions for two-photon exchange

Dmitry Borisyuk, Alexander Kobushkin

发表信息：
Phys.Rev.D79:034001,2009
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摘要：

在pQCD框架下研究了高Q^2下电子-核子弹性散射中的双光子交换。在玻恩近似下，得到的TPE振幅为α/α_s量级。它的形状和大小对核子波函数的选择很敏感，因此研究TPE效应可以提供有关核子结构的重要信息。采用基于QCD求和规则的波函数时，TPE对电子-质子截面的修正具有负号，在Q^2 = 30 GeV^2时几乎是线性的，并随Q^2的增大而增大，最大可达7%。现有的仅考虑核子中间态的“强子”计算结果，可以在Q^2 = 3 GeV^2附近与pQCD结果平滑地联系起来。在这一点以上，两种方法不一致，这意味着“强子”方法在高Q^2时变得不合适。其他相关的观测，如电子/正电子截面比，也进行了讨论。

英文摘要：

We study two-photon exchange (TPE) in the elastic electron-nucleon scattering at high Q^2 in the framework of pQCD. The obtained TPE amplitude is of order alpha/alpha_s with respect to Born approximation. Its shape and value are sensitive to the choice of nucleon wavefunction, thus study of TPE effects can provide important information about nucleon structure. With the wavefunctions based on QCD sum rules, TPE correction to the electron-proton cross section has negative sign, is almost linear in epsilon and grows logarithmically with Q^2 up to 7% at Q^2 = 30 GeV^2. The results of existing "hadronic" calculations, taking into account just the nucleon intermediate state, can be smoothly connected with pQCD result near Q^2 = 3 GeV^2. Above this point two methods disagree, which implies that "hadronic" approach becomes inadequate at high Q^2. Other relevant observables, such as electron/positron cross section ratio, are also discussed.

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