Boundary of Nuclear Physics and QCD

Recent progress in lattice QCD, combined with the imminent advent of a new generation of dedicated supercomputers and advances in chiral extrapolation mean that the next few years will bring quite novel insights into hadron structure. We review some of the recent highlights in this field, the questions which might be addressed and the experiments which may be expected to stretch that understanding to its limits. Only with a sound understanding of hadron structure can one hope to explore the fundamental issue of how that structure may change at finite density (or temperature). We explore potential future insights from lattice QCD into the phenomenon of nuclear saturation and a very important hint from recent data of a change in the structure of a bound nucleon.Comment: Invited talk presented at INPC2001, Berkeley, August 200

The spin structure function of the neutron

The neutron spin structure function, $g_{1n}$, has been of considerable interest recently in connection with the Bjorken sum rule and the proton spin crisis. Work on this problem has concentrated on measurements at low-$x$. We recall the important, non-perturbative physics to be learnt by going instead to larger values of $x$ and especially from a determination of the place where the expected sign change occurs. Of course, in order to obtain neutron data one must use nuclear targets and apply appropriate corrections. In this regard, we review recent progress concerning the various nuclear corrections that must be applied to measurements on polarised $^3$He.Comment: Invited presentation at the Workshop on the Spin Structure of the Proton and Polarized Collider Physics, ECT* Trento, July 23-28, 200

Bottom quark contribution to spin-dependent dark matter detection

We investigate a previously overlooked bottom quark contribution to the spin-dependent cross section for Dark Matter(DM) scattering from the nucleon. While the mechanism is relevant to any supersymmetric extension of the Standard Model, for illustrative purposes we explore the consequences within the framework of the Minimal Supersymmetric Standard Model(MSSM). We study two cases, namely those where the DM is predominantly Gaugino or Higgsino. In both cases, there is a substantial, viable region in parameter space ($m_{\tilde{b}} - m_\chi \lesssim \mathcal{O}(100)$ GeV) in which the bottom contribution becomes important. We show that a relatively large contribution from the bottom quark is consistent with constraints from spin-independent DM searches, as well as some incidental model dependent constraints.Comment: 11 pages, 10 figures, version published in NP

Electromagnetic Gauge Invariance of the Cloudy Bag Model

We examine the question of the gauge invariance of electromagnetic form factors calculated within the cloudy bag model. One of the assumptions of the model is that electromagnetic form factors are most accurately evaluated in the Breit frame. This feature is used to show that gauge invariance is respected in this frame.Comment: 8 pages, RevTex, 1 figure, to be published in Phys. Rev.

Overview of Issues Surrounding Strangeness in the Nucleon

The calculation of the strangeness content of the nucleon and its experimental verification is a fundamental step in establishing non-perturbative QCD as the correct theory describing the structure of hadrons. It holds a role in QCD analogous to the correct calculation of the Lamb shift in QED. We review the latest developments in the vector and scalar matrix elements of the strange quarks in the proton, where there has recently been considerable progress.Comment: Invited presentation at the 10th Conference on the Intersection of Nuclear and Particle Physics, San Diego, May 26-May 30, 200

Variation of hadron masses in finite nuclei

Using a self-consistent, Hartree description for both infinite nuclear matter and finite nuclei based on a relativistic quark model (the quark-meson coupling model), we investigate the variation of the masses of the non-strange vector mesons, the hyperons and the nucleon in infinite nuclear matter and in finite nuclei.Comment: 4 pages plus one ps file, to appear in Proc. of International Symposium on Non-Nucleonic Degrees of Freedom Detected in Nucleus (NNDF '96) at Osaka, Japa

Self-consistent description of finite nuclei based on a relativistic quark model

Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons which interact through the (self-consistent) exchange of scalar ($\sigma$) and vector ($\omega$ and $\rho$) mesons. The coupling constants and the mass of the $\sigma$-meson are determined from the properties of symmetric nuclear matter and the rms charge radius in $^{40}$Ca. Calculated properties of static, closed-shell nuclei from $^{16}$O to $^{208}$Pb are compared with experimental data and with results of Quantum Hadrodynamics (QHD). The dependence of the results on the nucleon size and the quark mass is investigated. Several possible extensions of the model are also discussed.Comment: 37 pages, 17 postscript figures are included, uses epsfig.sty, uuencoded Z-compressed .tar file (uufiles