16194652
Matching Perturbative and Non-Perturbative Physics With Power Accuracy in Heavy-Quark Effective Theory
I discuss a scheme to match perturbative and non-perturbative physics with power accuracy in the heavy-quark effective theory. I elaborate on two important aspects of the scheme: 1) a multi-loop subtraction of soft contributions from the perturbation series in the pole mass, 2) a perturbative regularization of the linearly-divergent heavy-quark self-energy in the lattice formulation of the heavy-quark effective theory.
55516651
A Beautiful Spin
Spin is a beautiful concept that plays an ever important role in modern physics. In this talk, I start with a discussion of the origin of spin, and then turn to three themes in which spin has been crucial in subatomic physics: a lab to explore physics beyond the standard model, a tool to measure physical observables that are hard to obtain otherwise, a probe to unravel nonperturbative QCD. I conclude with some remarks on a world without spin.
119403070
Resummation of Threshold Logarithms in Effective Field Theory for DIS, Drell-Yan and Higgs Production
We apply the effective field theoretic (EFT) approach to resum the large perturbative logarithms arising when partonic hard scattering cross sections are taken to the threshold limit. We consider deep inelastic scattering, Drell-Yan lepton pair production and the standard model Higgs production through gluon-gluon fusion via a heavy-top quark loop. We demonstrate the equivalence of the EFT approach with the more conventional, factorization-based methods to all logarithmic accuracies and to all orders in perturbation theory. Specific EFT results are shown for the resummation up to next-to-next-to-next-to leading logarithmic accuracy for the above-mentioned processes. We emphasize the relative simplicity by which we derive most of the results and more importantly their clear physical origin. We find a new relation between the functions f (q,g) in the quark and gluon form factors and the matching coefficients in Drell-Yanand Higgs production, which may explain their universality believed to hold to all orders in perturbation theory.
121939908
Nuclear matter properties in the relativistic random phase approximation
Abstract Nuclear matter properties at zero temperature are studied in terms of the relativistic σ-ω model, including the random phase approximation (RPA) contribution. At normal density, the medium polarization adds about −35 MeV of binding energy to the mean field result. The scalar and vector effective interaction strengths are fitted to the nuclear matter saturation conditions under various approximations for the energy functional including the RPA term. The effective mass and bulk modulus are calculated with these parameters. The relative importance of different contributions to the binding energy is analyzed.
117193137
Delta -> N gamma* Coulomb quadrupole amplitude in PQCD
We present a leading-order PQCD factorization formula for the helicity-flip Delta-->Ngamma(*) matrix element G(0) (Coulomb quadrupole amplitude C2), taking into account the transverse momenta of the quarks and the contribution from the gluons. In the large Q(2) limit, its scaling behavior acquires a double-logarithmic correction log(2)(Q(2)/Lambda(2)) compared with the standard scaling analysis, due to the contribution from the orbital motion of the small-x partons. Based on this and on the latest JLab experimental results of the C2-M1 ratio R-SM at Q(2)=3-4 GeV2, we make a phenomenological prediction for the latter at higher values of Q(2).
2998736
Final state interactions and gauge invariant parton distributions
Abstract Parton distributions contain factorizable final state interaction effects originating from the fast-moving struck quark interacting with the target spectators in deeply inelastic scattering. We show that these interactions give rise to gauge invariance of the transverse momentum-dependent parton distributions. As compared to previous analyses, our study demonstrates the existence of extra scaling contributions from transverse components of the gauge potential at the light-cone infinity. They form a transverse gauge link which is indispensable for restoration of the gauge invariance of parton distributions in the light-cone gauge where the gauge potential does not vanish asymptotically. Our finding helps to explain a number of features observed in a model calculation of structure functions in the light-cone gauge.
15148506
Baryon Spectroscopy at Beijing Electron Positron Collider
Baryons are the basic building blocks of our world. If we cut any piece of object smaller and smaller,we will ﬁnally reach the nucleons, i.e., the lightest baryons, and we cannot cut them smaller anyfurther. So without mention any theory, we know that the study of baryon structure is at theforefront of exploring microscopic structure of matter. From theoretical point of view, since baryonsrepresent the simplest system in which the three colors of QCD neutralize into colorless objectsand the essential non-Abelian character of QCD is manifest, understanding the baryon structure isabsolutely necessary before we claim that we really understand QCD.Spectroscopy has long proved to be a powerful tool for exploring internal structures and basicinteractions of microscopic world. Ninety years ago detailed studies of atomic spectroscopy resultedin the great discovery of Niels Bohr’s atomic quantum theory [1]. Forty to sixty years later, stilldetailed studies of nuclear spectroscopy resulted in Nobel Prize winning discoveries of nuclear shellmodel [2] and collective motion model [3] by Aage Bohr et al. Comparing with the atomic andnuclear spectroscopy at those times, our present baryon spectroscopy is still in its infancy [4].Many fundamental issues in baryon spectroscopy are still not well understood [5]. The possibilityof new, as yet unappreciated, symmetries could be addressed with accumulation of more data.The new symmetries may not have obvious relation with QCD, just like nuclear shell model andcollective motion model.Joining the new eﬀort on studying the excited nucleons, N