arXiv 0907.04512009-07hep-ph

手征微扰理论在质子康普顿散射中的预测能力

Predictive powers of chiral perturbation theory in Compton scattering off protons

V. Lensky, V. Pascalutsa

备注：: 24 pages, 9 figures, RevTeX4, revised version published in EPJ C
发表信息：: Eur.Phys.J.C65:195-209,2010
DOI：: 10.1140/epjc/s10052-009-1183-z

摘要：

本文在重子手征微扰理论（B $χ$ PT）的框架下研究了低能核子的Compton散射，包括π介子、核子和$Δ$（1232）自由度，直到并包括次-次-首阶（NNLO）.我们考虑了$p^2$、$p^3$和$p^4/\varDelta$阶的效应，其中$\varDelta\approx 300$ MeV为$Δ$ -共振激发能.这些都是“预测”的权力，在这个意义上说，没有未知的低能量常数进入，直到至少一个订单更高（即$p^4$）。估计的自然尺寸的基础上的$p^4$效应的理论不确定性，我们发现，这样的NNLO结果的不确定性是目前的实验数据的不确定性相比，低能康普顿散射。我们发现一个很好的协议与实验的横截面数据至少到π介子生产阈值。然而，对于质子的磁极化率，我们得到的值为$(4.0\pm 0.7)\times 10^{-4}$ fm $^3$，与当前的PDG值有很大的不同。与以前的$χ$ PT研究的康普顿散射，我们执行的计算在一个明显的洛伦兹协变的方式，避免从重子（HB）的扩展。最低阶的HB $χ$ PT和B $χ$ PT的极化率结果之间的差异被发现是可观的。我们讨论了HB $χ$ PT和B $χ$ PT中质子极化率的手征行为，希望在不久的将来能与格点QCD计算对抗。在研究一些极化观测，我们确定的制度，他们天真的低能膨胀开始打破，从而解决即将到来的精确测量在HIGS设施。

英文摘要：

We study low-energy nucleon Compton scattering in the framework of baryon chiral perturbation theory (B$χ$PT) with pion, nucleon, and $Δ$(1232) degrees of freedom, up to and including the next-to-next-to-leading order (NNLO). We include the effects of order $p^2$, $p^3$ and $p^4/\varDelta$, with $\varDelta\approx 300$ MeV the $Δ$-resonance excitation energy. These are all "predictive" powers in the sense that no unknown low-energy constants enter until at least one order higher (i.e, $p^4$). Estimating the theoretical uncertainty on the basis of natural size for $p^4$ effects, we find that uncertainty of such a NNLO result is comparable to the uncertainty of the present experimental data for low-energy Compton scattering. We find an excellent agreement with the experimental cross section data up to at least the pion-production threshold. Nevertheless, for the proton's magnetic polarizability we obtain a value of $(4.0\pm 0.7)\times 10^{-4}$ fm$^3$, in significant disagreement with the current PDG value. Unlike the previous $χ$PT studies of Compton scattering, we perform the calculations in a manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB) expansion. The difference between the lowest order HB$χ$PT and B$χ$PT results for polarizabilities is found to be appreciable. We discuss the chiral behavior of proton polarizabilities in both HB$χ$PT and B$χ$PT with the hope to confront it with lattice QCD calculations in a near future. In studying some of the polarized observables, we identify the regime where their naive low-energy expansion begins to break down, thus addressing the forthcoming precision measurements at the HIGS facility.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文