Exploration of the electric spin polarizability of the neutron in lattice QCD
Michael Engelhardt
备注：
7 pages, 6 figures; talk presented at the 29th International Symposium on Lattice Field Theory (Lattice 2011), Squaw Valley, California, USA, July 10-16, 2011
A scheme to calculate the electric spin polarizability of the neutron, based on a four-point function approach to the background field method, is presented. The connected contributions to this spin polarizability are evaluated within a mixed action calculation employing domain wall valence quarks on MILC asqtad sea quark ensembles. Results are reported for two pion masses, 759 MeV and 357 MeV.
Knowledge of the electric polarizability is crucial to understanding the interactions of hadrons with electromagnetic fields. The neutron polarizability is very sensitive to the quark mass and is expected to diverge in the chiral limit. Here we present results for the electric polarizability of the neutron, neutral pion, and neutral kaon on eight ensembles with nHYP-smeared clover dynamical fermions with two different pion masses (227 and 306 MeV). These are currently the lightest pion masses used in polarizability studies. For each pion mass we compute the polarizability at four different vol…
Electromagnetic polarizabilities are important parameters for understanding the interaction between photons and hadrons. For pions these quantities are poorly constrained experimentally since they can only be measured indirectly. New experiments at CERN and Jefferson Lab are planned that will measure the polarizabilities more precisely. Lattice QCD can be used to compute these quantities directly in terms of quark and gluons degrees of freedom, using the background field method. We present results for the electric polarizability for two different quark masses, light enough to connect to chiral…
We study the finite volume effects on the electric polarizability for the neutron, neutral pion, and neutral kaon using eight dynamically generated two-flavor nHYP-clover ensembles at two different pion masses: 306(1) and 227(2) MeV. An infinite volume extrapolation is performed for each hadron at both pion masses. For the neutral kaon, finite volume effects are relatively mild. The dependence on the quark mass is also mild and a reliable chiral extrapolation can be performed along with the infinite volume extrapolation. Our result is $α_{K^0}^\mbox{phys}=0.356(74) \times 10^{-4} \mbox{fm}^3$.…
Electric polarizability of neutral hadrons from dynamical lattice QCD ensembles
我们提出了一个价计算的电极化的中子，中性π介子和中性K介子的两个动态生成的nHYP-三叶草合奏。这些系综的π介子质量分别为227（2）MeV和306（1）MeV，这是极化率研究中使用的最低质量。这是在物理点上确定这些参数的程序的一部分。我们进行了一个高统计计算，使我们能够：（1）进行外推的K介子极化率的物理点，我们发现$α_K =0.269(43)\times10^{-4}$ fm $^{3}$，（2）定量比较我们的中子极化率的结果与预测从$χ$ PT，和（3）分析的依赖性的价和海夸克的质量。K介子极化率随轻夸克质量变化缓慢，外推结果可信度高。
We present a calculation of the charged pion electric polarizability using the background field method. To extract the mass-shift induced by the electric field for the accelerated charged particle we fit the lattice QCD correlators using correlators derived from an effective model. The methodology outlined in this study (boundary conditions, fitting procedure, etc.) is designed to ensure that the results are invariant under gauge transformations of the background field. We apply the method to four $N_f=2$ dynamical ensembles to extract $α_{π^\pm}$ at pion mass of $315$ MeV.
There has been much progress in the experimental measurement of the electric and magnetic polarizabilities of the nucleon. Similarly, lattice QCD simulations have recently produced dynamical QCD results for the magnetic polarizability of the neutron approaching the chiral regime. In order to compare the lattice simulations with experiment, calculation of partial quenching and finite-volume effects is required prior to an extrapolation in quark mass to the physical point. These dependencies are described using chiral effective field theory. Corrections to the partial quenching effects associate…
