44565255
Correlation effects in nuclear transparency.
The Glauber approximation is used to calculate the contribution of nucleon correlations in high-energy A(e,e'N) reactions. When the excitation energy of the residual nucleus is small, the increase of the nuclear transparency due to correlations between the struck nucleon and the other nucleons is mostly compensated by a decrease of the transparency due to the correlations between nondetected nucleons. We derive Glauber model predictions for nuclear transparency for the differential cross section when nuclear shell level excitations are measured. The role of correlations in color transparency is briefly discussed.
120657296
Quark confinement and hadronic interactions
A study of quark models for many-hadron systems is presented. The starting point in the construction of these nonrelativistic models is a proper formal definition of the concept of color singlet and nonsinglet clusters in a multiquark system which respects the exchange symmetry of the quarks. This definition provides a natural way to impose saturation of the confining forces. As a consequence, the resulting models are free from unphysical van der Waals forces whose presence is a characteristic difficulty in the conventional models based on superposition of two-body confining forces. The dynamics of the multiquark system are specified by defining the color projections of the Hamiltonian. These models make explicit the role of the color hidden dynamics in multihadron systems. The properties of these models are investigated in a study of the s-wave q2−q2 system. We develop new analytical methods appropriate for the study of many-body systems in the presence of confining interactions. These methods allow us to extract a variety of analytical results as well as exact numerical solutions, and they are employed to clarify the relation between the simple structure of the multiquark Hamiltonian and the wide variety of the resulting hadronic phenomena. The properties of bound and scattering states are studied for various models of the color hidden dynamics. Although the Hamiltonian contains only the confining force which determines the hadronic scale, phenomena are exhibited at a much lower energy scale. We investigate descriptions of the multiquark system in terms of hadronic degrees of freedom. Ambiguities in the formulation of such effective hadronic theories are discussed as well as their limitations in describing various physical observables. The fine tuning of the hadronic effective forces needed to generate the model phenomena which appear at a low-energy scale is understood from the underlying quark dynamics. Different signatures of quark degrees of freedom are studied, such as the appearance of threshold resonances or color hidden resonances, “EMC”-like modifications of the quark momentum distribution in hadronic bound states, or changes in the asymptotic behaviour of form-factors. The interdependence of these phenomenologically unrelated signatures is established, as well as their relation to properties of the color hidden dynamics.
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.
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.
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.
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.
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.