The theory of gravity is considered from the little group viewpoint. This leads to a theory with a constraint, which is equivalent to general relativity with an arbitrary cosmological term. With this framework (i) the cosmological constant cannot be put into the Lagrangian but it appears as an...

We consider two- and three-dimensional lattices with on each lattice a D-dimensional classical spin-vector. We restrict ourselves to nearest neighbour interactions which only depend on the angle between the spin-vectors. For these systems the bond-moving approximation of Migdal and Kadanoff is...

By numerical and analytical investigations we show that the bond-moving transformation of Migdal for planar spins on a two-dimensional lattice possesses a very rich structure. We find an infinite hierarchy of one-, three- and higher-dimensional fixed spaces. In addition to phase transitions of...

Using a Corner-type potential for the interaction between two monoaxial molecules, a simple equation has been derived for the angular dependence of the single particle distribution function. We investigate this equation for values of the molecular parameters not considered before. The usual...

An integrable SU(3) soin chain equation is constructed. An explicit form of the Lax-pair representation is given and it is shown to be gauge equivalent to a set of nonlinear Schrödinger- type equations for three complex variables.

In one space and one time dimension, a model of the nonlinear Boltzmann equation is presented that is exactly solvable for all initial conditions. Furthermore, this model has the following desirable properties: (i) conservation of the number of particles; (ii) energy conservation; (iii)...

The classical equations of motion of a continuum Heisenberg spin system in N dimensions are written in the form of equations for a particle field and a gauge field. Known results, such as the exact solution for N = 1 and the self-dual solution for N = 2, are recovered. Of the new results we...

We consider a mean field theory for nematic liquid crystals consisting of biaxial molecules. The internal degrees of freedom of the molecules are described by eight variables, three of which are the components of the angular momentum. The five remaining variables are the components of the...

In continuation of previous work we study the energy of infinite one-dimensional systems of particles interacting with the two-body potential ϕ (x) = (1 + x4)−1. We know beforehand that not for all values of the mean volume per particle a the equidistant configuration has minimum energy among...

The classical one-dimensional Heisenberg magnet is treated in the context of renormalization theory. This treatment is shown to be equivalent to the usual transfer matrix approach. If the chain consists of N spins, the original hamiltonian will, upon repeated application of the renormalization...