New upper bounds for the magnetization in ferromagnetic one-component systems

A collection of upper bounds on the magnetization in ferromagnetic one-component spin systems is derived from generalizations of the mean-field approximation. In particular, it contains sequences of bounds that converge to the true magnetization. The spin systems in question satisfy the GHS-inequality.Institut für Theoretische Physik, Universität Zürich, Zürich, Switzerland     

On the prosaic origin of the double poles in the sine-GordonS-matrix

We show that the apparently exotic double poles in the sine-GordonS-matrix are nothing but ordinary anomalous thresholds.This research was supported in part by the National Science Foundation under Grant No. PHY77-22864Max Kade Foundation Fellow. On leave of absence from the Institut für Theoretische Physik, Freie Universität Berlin, Federal Republic of Germany     

Stationary measures for the periodic Euler flow in two dimensions

We construct for the Euler flow in two dimensions with periodic boundary conditions the Gibbsian measures given by the energy and the enstrophy integrals. We show that they are inflnitesimally invariant under the Euler flow.On leave from Fakultät für Mathematik, Universität Bielefeld, Bielefeld, West Germany.On leave from Matematisk Institutt, Universitetet i Oslo, Oslo, Norway.     

Homogeneous Kähler manifolds: Paving the way towards new supersymmetric sigma models

Homogeneous Kähler manifolds give rise to a broad class of supersymmetric sigma models containing, as a rather special subclass, the more familiar supersymmetric sigma models based on Hermitian symmetric spaces. In this article, all homogeneous Kähler manifolds with semisimple symmetry groupG are constructed, and are classified in terms of Dynkin diagrams. Explicit expressions for the complex structure and the Kähler structure are given in terms of the Lie algebra g ofG. It is shown that for compactG, one can always find an Einstein-Kähler structure, which is unique up to a constant multiple and for which the Kähler potential takes a simple form.On leave of absence from Fakultät für Physik der Universität Freiburg, FRG     

String tension and glueball mass in a lattice theory of disconnected,selfintersecting random surfaces

We exhibit the analytic structure of a model of disconnected, selfintersecting random surfaces. This model is shown to have features attractive for a Monte Carlo simulation. Previously obtained numerical data show evidence that for a 3-dim embedding space the string tension vanishes above a critical temperature and has a critical exponent between 1 and 2. The glueball mass is shown to be bounded below by the mass-gap of the 3-dim Ising model.On leave of absence from Freie Universität Berlin     

Higher order perturbation theory for exponential Lagrangians: Third order

We define the vacuum expectation value of the time-ordered product of three exponentials of free massless fields as a continuous linear functional over a suitable test function space using minimal singularity as a criterion.Research sponsored by the Alfred P. Sloan Foundation.On leave from II. Institut für Theoretische Physik der Universität Hamburg, Germany.     

On the curvature of piecewise flat spaces

We consider analogs of the Lipschitz-Killing curvatures of smooth Riemannian manifolds for piecewise flat spaces. In the special case of scalar curvature, the definition is due to T. Regge; considerations in this spirit date back to J. Steiner. We show that if a piecewise flat space approximates a smooth space in a suitable sense, then the corresponding curvatures are close in the sense of measures.Supported in part by NSF MCS-810-2758-A-02Supported in part by Deutsche Forschungsgemeinschaft and NSF PHY-81-09110-A-01On leave of absence from Freie Universität Berlin     

Ergodic and topological properties of coulombic periodic potentials

The motion of a classical pointlike particle in a two-dimensional periodic potential with negative coulombic singularities is examined. This motion is shown to be Bernoullian for many potentials and high enough energies. Then the motion on the plane is a diffusion process. All such motions are topologically conjugate and the periodic orbits can be analysed with the help of a group.This work is part of a thesis submitted to Freie Universität Berlin     

The elastic behaviour of ferroelastic Sb5O7I polytype 2MC studied by ultrasonic experiments and Brillouin scattering

The temperature dependence of the elastic functions of the improper ferroelastic polytype 2MC-Sb₅O₇I has been investigated in the temperature range from room temperature to well above the structural phase transition atT _c=481 K. The stiffnessesc(c^*c^*),c(a,a),c ₂₂ andc(c^*a) show a considerable softening up to 20% aroundT _c whereasc ₄₄ remains unaffected by the phase transition. The experimental results are discussed considering cubic and quartic anharmonic coupling between two components of the zone boundary order parameter and elastic waves.Carried out in Laboratories RCA Ltd, Zürich, SwitzerlandCarried out in Fakultät für Physik der Universität, Regensburg, Federal Republic of Germany     

On Suhl's dispersion equations for dilute magnetic alloys in a finite magnetic field

The system of six coupled, nonlinear, singular integral equations, devised by Suhl to treat the problem of a spin 1/2 magnetic impurity in a finite magnetic field is shown to be reducible to a single integral equation. Analytic properties and symmetries of the system are discussed, which may serve as a guideline for numerical studies of the final integral equation. The first few steps of an iteration in terms of the magnetic field strength are carried out analytically.On leave from the Institut für Theoretische Physik der Universität Köln.     

A mechanical model of Brownian motion

We consider a dynamical system consisting of one large massive particle and an infinite number of light point particles. We prove that the motion of the massive particle is, in a suitable limit, described by the Ornstein-Uhlenbeck process. This extends to three dimensions previous results by Holley in one dimension.On leave of the Institut für Theoretische Physik I der Universität Münster. Supported by a Nato fellowshipSupported by NSF Grant, No. PHY 78-03816Supported by NSF Grant, Phy 78-15920     

Strict convexity of the pressure: A note on a paper of R. B. Griffiths and D. Ruelle

Strict convexity of the pressure of a quantum lattice gas is demonstrated in [1] with the help of a trace condition. An interpretation of that condition is given, and, simultaneously, an extension of the result of [1]. In particular, it is shown that the pressure is a continuous function of the lattice gas density.On leave of absence from the Institut für Theoretische Physik, Universität Göttingen, Fed. Rep. of Germany.     

Open quantum systems with time-dependent Hamiltonians and their linear response

We give a rigorous (Hamiltonian) treatment of a quantum system weakly coupled to an infinite free reservoir and subject to an external time-dependent driving potential varying on the scale of dissipation. The linear response of the system initially in thermal equilibrium is determined and compared with the usual expressions of linear response theory.Work partly supported by NSF grant no. MPS 75-11864-A04.On leave of absence from Fachbereich Physik der Universität München. Work supported by a DFG fellowship.     

Excimer laser processing of embedded fibers

Novel aspects of the excimer laser etching of nanostructures in embedded optical fibers are discussed. Emphasis is put on the etching of a specified hole geometry and on excellent surface quality of the hole walls.On leave from: Institute of Quantum Electronics, ETH, CH-8093 Zürich, Switzerland     

Discretized Boltzmann equation: Lattice limit and non-Maxwellian gases

We continue the study of a discrete model of the Boltzmann equation, in which the spatial variable is replaced by a finite periodic lattice. Using a weak compactness criterion forL ₁, the existence of a lattice limit as the lattice spacing tends to zero is proved. The case of unbounded collision kernels (non-Maxwellian gases) is also treated.This work was supported in part by National Science Foundation grant no. ENG-75 15882.On leave from Mathematisches Institut der Universität München, Federal Republic of Germany     

Zero-mass limit in perturbative quantum field theory

A newR-operation which satisfies Bogolubov-Parasiuk and Hepp recurrence and which is infrared and ultra violet convergent graph by graph, is defined in perturbative quantum field theory. This new subtraction scheme is used to achieve the zero-mass limit of a massive field theory.Chargé de recherche CNRS. — Work supported in part by Alexander Von Humboldt fellowship.Work supported in part by Deutsche Forschungsgemeinschaft. — Institut für theoretische Physik, Freie Universität Berlin, Berlin, Federal Republic of Germany, and present address: Radiological Research Laboratory, Columbia University, 630 West 168 St. New York, New York 10032, USA.     

Krein's spectral shift function and fredholm determinants as efficient methods to study supersymmetric quantum mechanics

A new method is proposed to study supersymmetric quantum mechanics. A basic relation is derived between Krein's spectral shift function and the Witten index as a powerful tool for explicit model investigations. The topological invariance of relevant quantities like the index, the anomaly, the spectral asymmetry and the spectral shift function is proved. As an illustration, some model calculations are presented, in particular the two-dimensional magnetic field problem, without assuming the magnetic flux to be quantized.Laboratoire associé au C.N.R.S.On leave of absence from Institut für Theoretische Physik, Universität Graz, A-8010 Graz, Austria.     

Laser-induced surface metallization of ceramic PLZT

Hot pressed, optically transparent ferroelectric ceramics of lanthanum modified lead zirconate titanate (PLZT) have been locally reduced and metallized by means of ultraviolet Kr⁺ laser irradiation in a hydrogen atmosphere. The technique allows maskless single-step metallic patterning of the material.On leave from Cietvielu Fizikas Institüts, Latvijas Valsts Universitäte, Riga, Latvian SSR, USSR     

The Jost-Schroer theorem for zero-mass fields

We extend the Jost-Schroer theorem to zero-mass fields in one time-dimension and arbitrarily many space-dimensions.On leave of absence from II. Institut für Theoretische Physik der Universität, Hamburg, Germany. Work supported by Stiftung Volkswagenwerk.