Electroweak interactions and exchange currents in nuclei

In the first part of the dissertation, a consistent model for the long-range part of the weak meson exchange currents (MEC) preserving basic symmetries of the strong interactions is developed within the framework of an hadronic field theory of nuclear structure (QHD). A model which builds the nucleon-nucleon interaction out of {dollar}\sigma,\ \omega{dollar} and {dollar}\pi{dollar} meson exchange is used to describe strong interactions in a nucleus. The scalar-pseudoscalar part of the problem coincides with the {dollar}\sigma{dollar}-model. In the linear realization of the sigma-model one obtains spatial axial exchange currents of order (1/M) in a non-relativistic decomposition in nucleon mass due to {dollar}\omega{dollar}-exchange. Consistency with the nuclear physics phenomenology requires the use of a very large {dollar}\rm m\sb{lcub}scalar{rcub},{dollar} and the low-mass {dollar}\sigma{dollar} cannot be introduced simply without breaking chiral invariance in this approach. A chiral transformation to the non-linear realization of the sigma-model is shown to be the natural way of treating the problem. PCAC is then satisfied identically for a one-body axial current even for a nucleon inside the nucleus. In this approach, the phenomenological low-mass {dollar}\sigma{dollar} can be incorporated in the model as a chiral singlet, still necessitating no additional exchange currents of order (1/M) to be present. Here the first appearance of the axial MEC is in the familiar {dollar}\pi{dollar}-exchange term of order {dollar}\rm (1/M\sp2){dollar} in the axial charge density. at the same time, there is now an additional relativistic one-body correction of order (1/M) in the spatial part of the weak axial current that is required to satisfy PCAC. These correction terms are included in a unified analysis of weak and electromagnetic processes with some selected light nuclei where transition densities have been previously determined from available electromagnetic data.;In the second part of the dissertation, a potential use of electroweak experiments with excited {dollar}(J\sp{lcub}\pi{rcub}T) = (0\sp+0){dollar} nuclear states in addition to the ground state with the same quantum numbers is discussed. Existing low momentum transfer {dollar}q\sp2{dollar} data on the inelastic charge form factor for the {dollar}\rm (0\sp+0)\sb{lcub}gnd{rcub}\to (0\sp+0)\sp{lcub}\*{rcub}{dollar} transition in {dollar}\rm\sp4He{dollar} are fit within simple nuclear models, and predictions are made for higher {dollar}q\sp2.{dollar}

The Axial-Vector Current in Nuclear Many-Body Physics

Weak-interaction currents are studied in a recently proposed effective field theory of the nuclear many-body problem. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The theory exhibits a nonlinear realization of $SU(2)_L \times SU(2)_R$ chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the axial-vector current and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of quantum chromodynamics, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to systematically expand the effective lagrangian in powers of the meson fields (and their derivatives) and to reliably truncate the expansion after the first few orders. Here it is shown that the expressions for the axial-vector current, evaluated through the first few orders in the field expansion, satisfy both PCAC and the Goldberger--Treiman relation, and it is verified that the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra. Explicit results are derived for the Lorentz-covariant, axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange currents can be deduced.Comment: 32 pages, REVTeX 4.0 with 12pt.rtx, aps.rtx, revsymb.sty, revtex4.cls, plus 14 figures; two sentences added in Summary; two references adde

PolyAnalyst data analysis technique

The data analysis techniques of the PolyAnalyst data mining system [Kiselev 94] are based on an automated synthesis of the functional programs treated as multi-dimensional nonlinear regression models. This approach provides the system with two valuable properties: 1) it can discover hidden in the data relations that might be of a great variety of forms, 2) it can explore arbitrarily complexly structured data when the corresponding data access primitives are provided. The paper contains a description of the final version of the basic PolyAnalyst mechanisms, which are utilized in the general case, as well as in a particular case of data organized as a set of attribute values (SAV), which is the most common format for the data explored by KDD methods. Numerous practical results obtained by the users of PolyAnalyst in various fields corroborate the high efficiency of the discussed approach to an automated discovery of numerical dependencies in the SAV-structured data