39848763
Effective hadron theories from a quark model.
In the context of the quark exchange model of Lenz et al., effective hadron theories are constructed and the resulting physical observables compared to their ''experimental'' values as defined by the calculations using the exact quark model operators. This model study illustrates convergence issues for an effective hadron basis in a quark model in which all physical observables can be computed exactly.
116005145
QUARK EXCHANGE AND NUCLEAR DYNAMICS
Publisher Summary This chapter provides an overview of the quark exchange and nuclear dynamics. Descriptions of nuclear structure and dynamics based upon nucleon degrees of freedom and effective interactions have proved quantitatively successful for a broad range of phenomena. The chapter discusses the duality between hadron and quark descriptions and also the limits of the hadronic description. The properties of isolated hadrons have guided construction of color-singlet confining forces in quark models. The color-hidden dynamics associated with the confinement mechanism can be investigated only with the interaction of two or more hadrons. Utilization of nuclear observables to learn about color non-singlet dynamics is a major issue that requires identification of the appropriate observables and perhaps of new modes of two and multi-hadron systems built upon the hidden color degree of freedom. Qualitative understanding of hadronic phenomena in terms of quark degrees of freedom, that is, the role of compositeness and color, is of primary importance.
121392258
Nuclear photoabsorption and Compton scattering at intermediate energy
Abstract Intermediate energy nuclear photoabsorption and Compton scattering within the Δ-hole approach are studied. The same Δ-nucleus dynamics used to describe a variety of pion-induced reactions are employed. A dynamical model for the photon-nucleon amplitude is constructed, including both resonant-channel and nonresonant backgrounds in addition to Δ-excitation. Medium corrections to the full amplitude are included for nuclear seattering. A doorway state expansion allows one to discuss quantitatively the role of various contributions to the Δ-hole Hamiltonian, thereby clarifying the level of sensitivity to the structure of the Δ spreading potential. The reactive content of the total cross section is diseussed. The results are compared with available photoabsorption data for 4 He, 12 C and 16 O. We present results for the Δ contribution to the electron seattering transverse response function, for coherent π 0 photoproduction, and for nuclear elastic Compton seattering. The photoabsorption strength is spread over a larger energy range by the Δ dynamics, in agreement with the data, but is centered at too high an energy. The helicity flip Compton cross section is especially sensitive to the Δ-nucleus interaction, such as the spin-orbit potential strength.
38852216
Pion optical potential with Delta dynamics.
A pion optical potential is constructed which incorporates the \ensuremath{\Delta} dynamics found to be important in \ensuremath{\Delta}-hole analyses of pion scattering from light nuclei. These dynamics include \ensuremath{\Delta} propagation, binding and Pauli blocking, and a \ensuremath{\Delta} spreading potential. We employ a local density approximation for the medium-modified \ensuremath{\Delta} propagator, resulting in a computationally flexible tool for the analysis of pion-nucleus data. We reproduce the \ensuremath{\Delta}-hole results for \ensuremath{\pi}${\mathrm{\ensuremath{-}}}^{16}$O scattering satisfactorily. Elastic ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$${\mathrm{\ensuremath{-}}}^{208}$Pb scattering is described very well with the same strongly damping spreading potential found for light nuclei. The pion wave functions in the medium are substantially modified by the \ensuremath{\Delta} dynamics.
121644079
Electronuclear physics with spin
Abstract The use of spin observables in intermediate energy electron scattering is reviewed. Results and status of the first generation experiments and new developments are summarized.
120864487
Propagation in nonlocal optical potentials
It is shown that a nonlocal optical potential implies multiple eigenmode propagation. This is important when the mean free path becomes of the order of the nonlocality, such as in the strong absorption situation occurring for pion scattering near the 3-3 resonance, and consequently the propagation cannot be described reasonably by one complex wave number. The eigenmode structure can be seen most directly in quasielastic scattering.
17521368
Quantization of the Bianchi type-IX model in supergravity with a cosmological constant.
Diagonal Bianchi type-IX models are studied in the quantum theory of $ N = 1 $ supergravity with a cosmological constant. It is shown, by imposing the supersymmetry and Lorentz quantum constraints, that there are no physical quantum states in this model. The $ k = + 1 $ Friedmann model in supergravity with cosmological constant does admit quantum states. However, the Bianchi type-IX model provides a better guide to the behaviour of a generic state, since more gravitino modes are available to be excited. These results indicate that there may be no physical quantum states in the full theory of $ N = 1 $ supergravity with a non-zero cosmological constant. are available to be excited. These results indicate that there may be no physical quantum states in the full theory of $ N = 1 $ supergravity with a non-zero cosmological constant.