Nucleon polarisabilities at and beyond physical pion masses
Nucleon polarisabilities at and beyond physical pion masses
复制标题
物理π介子质量及以上的核子极化率
DOI：
10.1140/epja/i2016-16139-5
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
D. Phillips
中科院分区：
文献类型：
--
作者：
H. Grießhammer;J. McGovern;D. Phillips
摘要：我们检查了质子和中子标量和自旋偶极极化率的手性有效场理论 ($ \chi$ EFT) 的结果，无论是物理介子质量还是 $ {m_{\pi}}$ 的函数。这为晶格 QCD 极化率计算提供了手性外推。我们包括核子π介子云的主导效应和次主导效应，以及 $\Delta$(1232) 共振及其π介子云的主导效应。分析结果在 N2LO 处完成，$ δ$ 计数接近物理值的 π 介子质量，并且在类似于 δ 核子质量分裂的 π 介子质量的领先顺序上。为了量化我们预测的截断误差并拟合为 68% 置信度区间，我们使用最近适应 EFT 扩展的贝叶斯过程。在物理点上，我们对自旋极化率的预测在各自的误差范围内与使用实验和色散关系理论的替代提取非常一致。在较大的π介子质量下，我们发现当 $ {m_{\pi}}$ 接近约 300 MeV 时，所有极化率的手性展开本质上变得不可靠——正如在其他可观测值中已经看到的那样。 $ \chi$ EFT 还预测了电标量极化率和磁标量极化率在物理点上方存在显着的同位旋分裂；我们推测这对核子稳定性的影响。我们的结果与 $ \chi$ EFT 收敛领域中新兴的点阵计算非常吻合。奇怪的是，对于我们一些预测的中心值，这一一致性在更高的π介子质量下仍然存在。我们推测这是否不仅仅是一个偶然的巧合。
Abstract.We examine the results of Chiral Effective Field Theory ($ \chi$ EFT) for the scalar- and spin-dipole polarisabilities of the proton and neutron, both for the physical pion mass and as a function of $ {m_{\pi}}$. This provides chiral extrapolations for lattice QCD polarisability computations. We include both the leading and subleading effects of the nucleon’s pion cloud, as well as the leading ones of the $ \Delta$(1232)-resonance and its pion cloud. The analytic results are complete at N2LO in the $ \delta$ counting for pion masses close to the physical value, and at leading order for pion masses similar to the Delta-nucleon mass splitting. In order to quantify the truncation error of our predictions and fits as 68% degree-of-belief intervals, we use a Bayesian procedure recently adapted to EFT expansions. At the physical point, our predictions for the spin polarisabilities are, within respective errors, in good agreement with alternative extractions using experiments and dispersion-relation theory. At larger pion masses we find that the chiral expansion of all polarisabilities becomes intrinsically unreliable as $ {m_{\pi}}$ approaches about 300 MeV --as has already been seen in other observables. $ \chi$ EFT also predicts a substantial isospin splitting above the physical point for both the electric and magnetic scalar polarisabilities; and we speculate on the impact this has on the stability of nucleons. Our results agree very well with emerging lattice computations in the realm where $ \chi$ EFT converges. Curiously, for the central values of some of our predictions, this agreement persists to much higher pion masses. We speculate on whether this might be more than a fortuitous coincidence.
影响因子：
8.6
作者：
Epelbaum, E.;Krebs, H.;Meissner, U. -G.
通讯作者：
Meissner, U. -G.