Table of contents

In this paper we have constructed the multiparticle (q, p)-realization of the su(1, 1) Lie algebra, and studied its relation to the multimode bosonic realization and squeezing properties. We believe that this multiparticle realization should be very useful in the study of a system of coupled general time-dependent quantum oscillators whose Hamiltonian can be written as a linear combination of the three su(1, 1) generators; in particular, it is more capable to give a vivid picture of the system in the configuration space.

We argue that in systems with finite Hilbert spaces, the quantum-kinematical constraint imposed by the identity of particles on the associated Hilbert spaces has a classical counterpart: the corresponding classical phase spaces exhibit non-trivial topological differences depending on whether such particles are distinguishable or not. We show this explicitly in the context of the two-interacting-spin model with axial anisotropy.

We show how thermo field vacuum states can be related to phase and angle states and to Greenberg's infinite statistics.

An equilibrium superfluid is usually modelled by a Bose gas below its transition temperature. Here we compute rigorously the deviation from normality of the angular-momentum fluctuations, and prove that the extremal phases, or the extremal equilibrium state components, show normal behaviour, except for special boundary conditions.

We calculate the generic parameter dependence of the topological entropy at the onset of pruning: for a family of generalized Baker transformations the deviation of the topological entropy from its maximum value grows with a power law on which a self-similar fine structure is superimposed. Interpreting the onset of pruning as a boundary crisis in the regime of transient chaos, we can derive the exponent of the power law. In addition, an algorithm is presented that allows to calculate the fine structure. The results agree excellently with numerical data that are presented for maps describing conservative as well as dissipative systems. It is argued that the results hold for generic Lorenz-like maps.

New lower limits on the half-lives for ββ decay of ⁹⁶Zr and ¹⁵⁰Nd to excited states of ⁹⁶Mo and ¹⁵⁰Sm have been obtained. They range between 1 · 10¹⁹ and 4 · 10¹⁹ years (90% c.l.). The measurements were performed while searching for the de-excitation gamma rays of the daughter nuclide with a germanium detector. In addition, single-β decay of ⁹⁶Zr has also been studied, providing a half-life for this process longer than 3.8 · 10¹⁹ y (90% c.l.).

The shift of Ne X Lyman lines in laser plasmas is calculated by using a self-consistent potential and an inhomogeneous quasi-static field to account for electrons and ion perturbers, respectively. Our results agree with those of other self-consistent models in which the distributions of perturbers are Boltzmann-like. We also examine the effect of electron screening on the E1-transition probabilities.

We present a new type of lattice for trapping cold atoms in nearly-dark states where they weakly interact with light. The periodic potential is obtained with fields in a lin ⊥ lin configuration tuned on the blue side of a J → J transition and in the presence of a uniform static magnetic field. A numerical analysis performed for J = 4 demonstrates the occurrence of very small absorption widths and large populations in the lowest vibrational states. These lattices should be interesting for increasing the atomic density and for observing delocalized atomic wave functions.

We examine the average 2-point monomer correlation function of distinct polymer chains in solution, and discuss the effect of repulsion when two polymer clouds are close to each other. A prediction is given for the asymptotic behaviour of the distinct structure function, which varies as q^-d in good solvents. This dependence is discussed in terms of the field-theoretical analog, revealing also the contribution of a higher non-analytic q-dependent term. The prediction for the asymptotic behaviour is confronted to a neutron small-angle scattering experiment in a semi-dilute polymer solution.

The dynamics near the glass transition in a two-dimensional lattice model of polymer melt is studied by Monte Carlo simulation. Mean-square displacements of the individual monomers as well as of the centres of mass of the polymers are observed for over seven decades of time which provide quite reliable equilibrated values (corresponding to the results from a quasi-static cooling measurement) of the diffusion constant. The diffusion constants are determined as a function of temperature and size of the lattice (keeping the density of the monomers and the degree of polymerization fixed). A striking size dependence is shown by the diffusion constant at low temperatures, which suggests the possibility of the existence of strongly cooperatively rearranging regions in the system, as was postulated by Adam and Gibbs. Our results indicate the increase of the mean size of such regions as the temperature is lowered.

The glass transition temperature of thin polystyrene films has been measured as a function of film thickness. It is found that the glass transition decreases in temperature as the thickness of the film is reduced. The effect is not strongly molecular-weight dependent, ruling out chain confinement as the major cause; instead we suggest that at the surface of the glassy film a liquidlike layer exists whose size diverges as the glass transition temperature is approached from below.

A new method is given for calculating the electronic structure of solids, enabling finite-difference methods to be used for systems with deep atomic potentials. In muffin-tin spheres around the nuclei, the atomic wave functions are determined using standard numerical techniques. They are then matched onto a finite-difference grid in the interstitial region by an embedding procedure by which the interior of a muffin-tin is replaced by an embedding potential at its boundary. The sparse Hamiltonian matrix of the grid can be diagonalized using methods with time scaling linear with the system size. We present results for f.c.c. copper.

We draw the attention to a class of cosmological models which exhibits a friction term for the cosmological fluid, and we show that the friction is equivalent to an inflaton field. The issuing inflationary scenario, which we called frinflation, does not need a subsequent reheating phase and it solves in a simple way the graceful exit problem.