Particles and Classical-Like Theories

X. Xia, R. Silbey

A classical field theory is constructed to describe the interacting classical particles in one-dimensional (1D) channels. We show the intrinsic connection between the classical field theory and the corresponding quantum theory, i.e., Tomonaga-Luttinger liquid theory, which describes the interacting fermions in 1D. As applications, we calculate the particle density function along the tube axis and the particle current through the channels by explicitly including the particle-particle and particle-wall interactions and we find quantum-classical correspondence in the conductance formula.

N. Rosen

J. J. Halliwell

We use the decoherent histories approach to quantum theory to derive the form of an effective theory describing the coupling of classical and quantum variables. The derivation is carried out for a system consisting of a large particle coupled to a small particle with the important additional feature that the large particle is also coupled to a thermal environment producing the decoherence necessary for classicality. The effective theory is obtained by tracing out both the environment and the small particle variables. It consists of a formula for the probabilities of a set of histories of the large particle, and depends on the dynamics and initial quantum state of the small particle. It has the form of an almost classical particle coupled to a stochastic variable whose probabilities are determined by a formula very similar to that given by quantum measurement theory for continuous measurements of the small particle's position. The effective theory gives intuitively sensible answers when the small particle is in a superposition of localized states (unlike the simple mean field approach of coupling to the expectation values of the small system). The derived effective theory suggests a form of the semiclassical theory even when the quantum theory of the large system is not known, as is the case, for example, when a classical gravitational field is coupled to a quantized matter field, thus offering a new approach to the back reaction problem.

Salvator Cannavo

A. Horzela, E. Kapuścik

An alternative picture of classical many body mechanics is proposed. In this picture particles possess individual kinematics but are deprived from individual dynamics. Dynamics exists only for the many particle system as a whole. The theory is complete and allows to determine the trajectories of each particle. It is proposed to use our picture as a classical prototype for a realistic theory of confined particles.

Peter Bongaarts