Phenomenology of Hadrons and Fundamental Particles

[01403621]本基金将研究三个课题，涵盖核理论和粒子理论。1)风味对称性。PI和他的研究生（部分由这笔拨款资助）将研究三代费米子之间可能的“风味”对称性，特别是最近和即将到来的中微子质量和混合实验结果对它们施加的限制。需要考虑的其他约束来自于改变风味的中性电流过程和质子衰变的限制。这些研究的目的是为了回答这样一个问题：为什么会有三代的费米子被复制出来，而它们的质量和混合成分却大相径庭。2)大N极限中的重子。PI将在具有大量N个色电荷（大N）的QCD的众多成功的基础上研究重子共振动力学。这些粒子现在正在杰斐逊实验室大量生产，但目前用于研究它们的理论工具有限。特别是，PI将寻求与模型无关的结果，这些结果不仅考虑到大N膨胀，而且考虑到介子和核子之间耦合所隐含的手性对称性（共振衰减到此）。强子量的严格QCD约束。从色散关系中强加的约束允许人们甚至在非摄动状态下对QCD振幅作出精确的陈述。一方面得到了夸克和胶子参数等基本量与形状因子等测量量之间的关系。这些关系可以提供关于强交互作用方式的微妙和高度重要的信息，并形成这项工作的动机。PI将继续这一成功的计划，以考虑诸如扩大适用范围和包括来自渐近自由区域的附加信息等情况。

0140362LebedThree topics will be investigated under this grant, spanning both nuclear and particle theory.1) Flavor Symmetries. The PI and his graduate dissertation student (partially funded by this grant) will investigate possible "flavor" symmetries among the three fermion generations, especially the constraints imposed upon them by recent and forthcoming experimental results on neutrino masses and mixing. Additional constraints to be taken into account arise from limits on flavor-changing neutral current processes and proton decay. These studies are designed to work toward answering the question of why there are three replicated generations of fermions with nonetheless widely differing masses and mixings.2) Baryons in the Large N Limit. The PI will build upon the numerous successes of QCD with a large number N of color charges (large N) to study the dynamics of baryon resonances. These particles are now being produced in huge numbers at Jefferson Lab, but the theoretical tools currently used to study them are limited. In particular, the PI will seek model-independent results that respect not only the large N expansion, but also the chiral symmetry implied by coupling among pions and nucleons (to which the resonances decay).3) Rigorous QCD Constraints on Hadronic Quantities. The imposition of constraints from dispersion relations allows one to make precise statements about QCD amplitudes even in the nonperturbative regime. One obtains relations between fundamental quantities such as quark and gluon parameters on one hand, and measured quantities such as form factors on the other. These relations can provide subtle and highly nontrivial information on the way that the strong interaction works, and form the motivation for this work. The PI will continue this successful program to consider such cases as expanding the range of applicability and including additional information from the region of asymptotic freedom.