Role Of Symmetry In Dynamics Research Articles

Reply to Isgur’s comments on valence QCD

With the goal of understanding the complexity of QCD and the role of symmetry in dynamics, the authors studied a field theory called Valence QCD (VQCD) in which the Z graphs are forbidden so that the Fock space is limited to the valence quarks. The authors calculated nucleon form factors, matrix elements, and hadron masses both with this theory and with quenched QCD on a set of lattices with the same gauge background. Comparing the results of the lattice calculations in these two theories, the authors drew conclusions regarding the SU(6) valence quark model and chiral symmetry. While recognizing the goal of VQCD, Nathan Isgur disagrees on some of the conclusions the authors have drawn. The foremost objection raised in section 2 is to their suggestion that the major part of the hyperfine splittings in baryons is due to Goldstone boson exchange and not one-gluon-exchange (OGE) interactions. The logic of Isgur's objection is that VQCD yields a spectroscopy vastly different from quenched QCD and therefore the structure of the hadrons (to which hyperfine splittings in a quark model are intimately tied) is also suspect so no definite conclusions are possible. To put this into perspective it should be emphasized atmore » the outset that spectroscopy is only one aspect of hadron physics examined in section 1. The authors have studied the axial and scalar couplings of nucleon in terms of F{sub A}/D{sub A} and F{sub S}/D{sub S}, the neutron to proton magnetic moment ratio {mu}n/{mu}p, and various form factors. None of these results reveal any pathologies of hadron structure and turn out to be close to the SU(6) relations, as expected. In fact this is what motivated the study of valence degrees of freedom via VQCD. In section 2 the authors address specific issues related to spectroscopy in VQCD. Isgur also presented more general arguments against the idea of boson exchange as a contributor to hyperfine effects. A cornerstone of his discussion is the unifying aspect of OGE in a quark model picture. The authors believe that it is also natural and economical to identify chiral symmetry as the common origin for much of the physics being discussed here. Therefore in section 3 the authors take the opportunity to sketch out an effective theory that may serve as a framework to interpret the numerical results of VQCD.« less

Dynamic symmetries in nuclei

The role of dynamic symmetries in nuclei is briefly reviewed.

Dynamical symmetries in nuclear weak interactions

The role of dynamic symmetries in the study of nuclear -decay and other weak-interaction processes is discussed.

Physics of high-spin states in the interacting boson model

The physics of high-spin states is discussed within the framework of the interacting boson model. Three topics are specifically addressed: (i) high-spin states; (ii) superdeformation; (iii) the role of dynamic symmetries in superdeformed bands.

The role of dynamic symmetries in hadronic structure

The role of spectrum generating algebras (SGA) and dynamic symmetries (DS) in hadronic structure is briefly reviewed.

The role of dynamic symmetries and supersymmetries in nuclear physics

The role played by dynamic symmetries and supersymmetries in nuclear physics is discussed. Experimental examples are shown. The implications to other fields of physics are briefly reviewed.

The role of dynamic symmetries and supersymmetries in nuclear physics: F. Iachello. Center for Theoretical Physics, Sloane Laboratory, and A. W. Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06511

The role of dynamic symmetries in physics is discussed, with particular emphasis to nuclear structure physics. The dynamic symmetries of the interacting boson model, with dynamic algebra U(6), are introduced and experimental examples are presented. Dynamic symmetries provide a classification scheme for even-even nuclei. Symmetries are further enlarged to supersymmetries, involving both fermionic and bosonic degrees of freedom. The dynamic supersymmetries of the interacting boson-fermion model, with dynamic superalgebra U(6/{Omega}), where {Omega} is the dimension of the fermionic space, are introduced and experimental examples presented. Supersymmetries provide a classification scheme for odd-even, even-odd and odd-odd nuclei.