11577820
Light Front Nuclear Theory and the HERMES Effect
I discuss the use of light cone variables to compute the nucleonic and mesonic components of nuclear wave functions. A Lagrangian and its energy-momentum tensor $T^{^+\mu}$ is used to define the total momentum operators $P^\mu$. The aim is to use wave functions, expressed in terms of plus-momentum variables, which are used to analyze high energy experiments such as deep inelastic scattering, Drell-Yan production, (e,e') and (p,p') reactions. We discuss infinite nuclear matter within the mean field approximation; finite nuclei using the mean field approximation; nucleon-nucleon scattering, within the one boson exchange approximation; and, infinite nuclear matter including the effects of two-nucleon correlations. Standard good results for nuclear saturation properties are obtained, with a possible improvement in the lowered value, 180 MeV, of the computed nuclear compressibility. In our approach, manifest rotational invariance emerges at the end of the calculation. Thus nuclear physics can be done in a manner in which modern nuclear dynamics can be implemented and symmetries are respected. A salient feature is that $\omega,\sigma$ and $\pi$ mesons are obtained as important constituents. These can contribute coherently to enhance nuclear electroproduction cross sections for longitudinal virtual photons at low $Q^2$, while depleting the cross section for transverse photons. Thus the recent HERMES inelastic lepton-nucleus scattering data at low $Q^2$ and small $x$ can be described using photon-meson and meson-nucleus couplings which are consistent with constraints obtained from meson decay widths, nuclear structure, deep inelastic scattering, and lepton pair production data. Our model makes a variety of testable predictions.
356245
Current algebra and the cloudy-bag model.
Two versions of the cloudy-bag model (surface and volume coupling) satisfy the commutation relations of current algebra. Perturbation-theory evaluations of various observables are compared for the two treatments. The electromagnetic properties are essentially the same in both versions. The volume-coupling model contains, in lowest order, a pion-quark contact interaction that contributes to the axial-vector current. Including the effect of this term leads to a computed value of g/sub A/ of about 1.25, if the radius of the nucleon bag is around 1.0 fm.
119513589
Shapes of the proton
A model proton wave function, constructed using Poincar\'e invariance and constrained by recent electromagnetic form factor data, is used to study the shape of the proton. Spin-dependent quark densities are defined as matrix elements of density operators in proton states of definite polarization, and shown to have an infinite variety of nonspherical shapes. For high momentum quarks with spin parallel to that of the proton, the shape resembles that of a peanut, but for quarks with antiparallel spin the shape is that of a bagel.
122904929
Isobar dynamics and pion-nucleus elastic scattering
Abstract A new formalism is developed for studying pion-nucleus scattering in a model which takes into account the dynamics of the (3, 3) pion-nucleon resonance, or Δ isobar. This treatment is used to calculate π + elastic scattering from 16 O, 40 Ca, 48 Ca and 208 Pb at energies from 114 to 240 MeV. Some results for π − elastic scattering are also given. From fits to π + scattering data it is found that the Δ-nucleus interaction is well described by a spherical local complex potential proportional to the nuclear density. The central strength of this potential depends on energy but not on nuclear mass number. Some difficulties in determining the parameters of this potential from elastic scattering are discussed.
120464871
Deuteron photodisintegration: Impulse approximation and gauge invariance
We study the question of whether calculations of deuteron photodisintegration respect gauge invariance, and show that the impulse approximation is in severe disagreement with gauge invariance. The method in which Siegert's theorem is implemented is consistent with gauge invariance to within ten percent. We introduce a modification of the impulse approximation in which the current is conserved exactly. For deuteron photodisintegration this method yields essentially the same results as that of Partovi. Our method can easily be applied to electron- or neutrino-nucleus scattering.
118854850
Polarized quark distributions in nuclear matter
We compute the polarized quark distribution function of a bound nucleon. The chiral quark-soliton model provides the quark and antiquark substructure of the nucleon embedded in nuclear matter. Nuclear effects cause significant modifications to the polarized distributions, including an enhancement of the axial coupling constant.
111136184
An Improved Control System for Van De Graaff Accelerators
In an effort to improve the energy stability and operating convenience of the Rutgers-Bell FN Tandem, a study has been made of the processes involved in the standard Van de Graaff corona stabilization system. In the light of these observations, a terminal voltage control system has been designed using error signals derived both from the slit system and the capacity pickoff plates. The system operates using either the standard slit system, or the machines' Generating Voltmeter as the terminal voltage reference, switching automatically to the G. V. system when beam is lost for any reason.
7944762
Towards a Cosmological Dual to Inflation
We derive all single-field cosmologies with unit sound speed that generate scale invariant curvature perturbations on a dynamical attractor background. We identify three distinct phases: slow-roll inflation; a slowly contracting adiabatic ekpyrotic phase, described by a rapidly-varying equation of state; and a novel adiabatic ekpyrotic phase on a slowly expanding background. All of these yield identical power spectra. The degeneracy is broken at the 3-point level: unlike the nearly gaussian spectrum of slow-roll inflation, adiabatic ekpyrosis predicts large non-gaussianities on small scales.
119233886
On the origin of gravitational Lorentz covariance
We provide evidence that general relativity (GR) is the unique spatially covariant effective field theory of the transverse, traceless graviton degrees of freedom. The Lorentz covariance of GR, having not been assumed in our analysis, is thus plausibly interpreted as an accidental or emergent symmetry of the gravitational sector.