Volume 30, Issue 1, January 1999
30(1999); http://dx.doi.org/10.1134/1.953095View Description Hide Description
The experimental evidence for the existence of resonance states in light-quark systems, manifested as resonances of various masses, is reviewed. The characteristic feature of these resonances is the existence of various energy states for a given spin and parity. Such resonances in the πππ system, created diffractively, are radial excitations of light-quark systems.
30(1999); http://dx.doi.org/10.1134/1.953096View Description Hide Description
The connection between the neutron mean squared intrinsic charge radius and the neutron–electron scattering length measured in low-energy neutron physics is discussed. Special attention is paid to the validity of the Foldy formula giving this connection. It is shown that there are two different ways of deriving the Foldy formula. A table is presented of the experimental data obtained during the period 1947–1997 which allow the determination of These data split into two groups. One group leads to and the other (including the Dubna data) to The sources of possible systematic errors in the experiments are discussed. In particular, the effect of resonance nuclear scattering on the measured value of is studied. The experimental results on the measurement of in low-energy neutron physics are compared with the theory. It is shown that if the data leading to are correct, then the modern theoretical ideas about the structure of the neutron (including the well developed Cloudy Bag Model) must be fundamentally changed.
30(1999); http://dx.doi.org/10.1134/1.953097View Description Hide Description
We discuss the S-matrix interpretation of perturbation theory for the Wigner-function generating functional at finite temperature. For the sake of definiteness the concrete particle-physics problem of high-temperature initial-state dissipation into a cold state is considered from the experimental and theoretical points of view. The temperature is introduced in the theory in a typical microcanonical way. The perturbation theory contains two-temperature (of the initial and final states) Green functions. Two possible boundary conditions are considered. One of them is the usual one in a field-theory vacuum boundary condition. The corresponding generating functional of the Wigner functions can be used in particle physics. Another type of boundary condition assumes that the system under consideration is in the environment of black-body radiation. This leads to the usual Kubo–Martin–Schwinger boundary condition in the equilibrium (one-temperature) limit. The comparisons of the S-matrix approach with Schwinger–Keldysh real-time finite-temperature field theory and with the nonstationary statistical-operator approach of Zubarev are considered. The range of applicability of the finite-temperature description of dissipation processes is shown.
30(1999); http://dx.doi.org/10.1134/1.953098View Description Hide Description
This review is devoted to problems associated with the study of dynamical systems with a finite number of degrees of freedom possessing local symmetry. The procedure of reduction of the system of dynamical equations to the normal form, where the Cauchy problem has a unique solution, is discussed within the framework of the classical Lagrangian and Hamiltonian theory. Special attention is given to the geometrical reduction scheme, which allows the physical subspace in the phase space of a degenerate dynamical system to be distinguished, and makes it possible to find the explicit form of the corresponding canonical variables without introducing additional gauge-fixing conditions (gauges) into the theory. The two reduction procedures, the geometrical method and the gauge-fixing method, are compared in order to understand what conditions on the gauges guarantee the correctness of the reduction procedure.
The generalized continuous analog of Newton’s method for the numerical study of some nonlinear quantum-field models30(1999); http://dx.doi.org/10.1134/1.953099View Description Hide Description
A numerical method for studying nonlinear problems arising in mathematical models of physics is systematically described in this review. The unified basis for the development of numerical schemes is a generalization of the continuous analog of Newton’s method, which represents a qualitatively new development of the Newtonian evolution process on the basis of the integration of concepts from perturbation theory and the theory of evolution in parameters. The results are presented of numerical studies of quantum-field models of the polaron, the solvated electron, the binucleon, and also QCD potential models for some commonly used potentials.