Table of contents

A new approach to quantum gravity is proposed which is free of the singularity which appears at the gravitational collapse in Einstein's field equations. An essential element in this model is that matter is considered to be a self-sustained structure of zero-point fluctuations of the vacuum. In this model, the presence of matter leads to a kind of elastic deformation of the vacuum, characterized by a lowering of the vacuum energy density with a 1/r dependence. The resulting noncancellation of the vacuum pressure, exerted on an object, is identified as gravity.

In order to study the limits of validity of ultrametricity we imagine a system composed of two SK models weakly coupled among themselves. For this case one assumes, as usual, that each one of them separately obeys ultrametricity while it is an open question whether the relevant configurations of the total system intended as a whole can be so classified. For zero coupling the andwer is trivially negative. For arbitrarily small interaction energy, provided it is extensive, an analysis of the associated generalized random energy models suggests that ultrametricity is recovered.

We study some properties of the ultrametric tree structure associated with the directed polymer problem. We find that the exponents 2/3 and 1/3 appear in a natural way in the description of the tree. Some of our results explain earlier numerical results of Zhang in the problem of the stability of the best directed polymer configuration to small perturbations.

Applying Mori's formalism to energy-dependent phase space density operators, we derive transport equations for electrons moving in a dynamic random potential. In the absence of electron-phonon coupling, electronic localization is obtained through Götze's mode coupling approximation. In the presence of electron-phonon interaction we find equations which have exactly the same structure as the multiple-trapping equations for electronic transport in amorphous semiconductors. Microscopic expressions for the capture and release rates occurring in these equations are given.

Yang-Mills theory in D = 7 with arbitrary gauge group G is considered. By use of the octonionic algebra we reduce D = 7 Yang-Mills equations to the nonlinear ordinary differential equations (Ward equations). As an example, we write out the explicit form of some solutions, which are the seven-dimensional analogues of the d = 4 instanton.

A strong hysteretic behaviour has been observed for the self-focusing of a c.w. laser beam focused in a four-component micellar phase near a sponge phase in the phase diagram. All data demonstrate that the laser wave induces a structural change from the micellar phase towards a phase of droplets the nature of which is discussed. The recorded limit cycles and "creep" of cycles allow an analogy with the magnetization of a ferromagnetic material to be developed.

We have observed the vacuum Rabi splitting on a beam of Rydberg atoms resonantly coupled to a high-Q superconducting cavity mode. The splitting is resolved down to five atoms on average inside the cavity and only three atoms resonant with the mode.

We report simulations of the velocity autocorrelation function (VACF) of a tagged particle in a four-dimensional lattice gas cellular automaton (LGCA). We observe a hydrodynamic tail in the VACF, which decays as t^-2, in agreement with the theoretical predictions. However, in a quantitative comparison, the simulations show that mode-coupling theory underestimates the amplitude of the hydrodynamic tail by (15 ÷ 60)%. The artificial correlations, previously observed in the projected three-dimensional lattice gas model, are found to be absent in this truly 4D model.

Brillouin and neutron-scattering measurements of TA-phonon branches are reported for SrTiO₃ at small wave vectors and at temperatures well below the 105 K structural transition. Anomalous softening in the former measurements, and dispersion in the latter, are found in the quantum paraelectric regime. Furthermore, an unexpected loss of scattered intensity is observed on the TA[100]-phonon branch at temperatures centred around 30 to 40 K.

The electronic structure of undoped and K-doped C₆₀ has been investigated by high-energy electron energy-loss spectroscopy in transmission. Information on the filling and energetic position of π*-levels as a function of dopant concentration is obtained. From momentum-dependent measurements it is concluded that for undoped and doped C₆₀ the π-bands are narrow indicating a weak interaction between the C₆₀ molecules.

A discontinuity jump occurs in a reflectivity curve at the total reflection edge when the reflecting surface is characterized by a long-range attractive potential V(z). We give a simple derivation of the result. Using a system of high molecular weight polymer chains in good solvent adsorbed at the free surface, we observe for the first time the predicted effect.

In near-critical fluids the critical fluctuations interact via a dipolar interaction in stationary electric field and the structure factor becomes uniaxial. As a result electric birefringence and dichroism are enhanced on approaching to criticality. A general formula for the effects is presented in the steady case for arbitrary wavelength of probing light. Another formula for transient electric birefringence can well explain a nonexponential decay observed by experiments. The nonlinear dielectric constant in stationary field is also calculated.

Erratum for Europhys. Lett.12 (6) 519-521 (1990)

Erratum for Europhys. Lett.15 (8) 815-820 (1991)