Low-energy theorems in Higgs physics

We present low-energy theorems for the calculation of loop amplitudes with external scalar or pseudoscalar Higgs bosons which are light compared to the loop particles. Starting from existing lowest-order versions of these theorems, we show how their applicability may be extended to the two-loop level. To illustrate the usefulness of these theorems, we discuss a number of applications to Higgs production and decay at and beyond the one-loop order.     

On completeness of the spectral domain of harmonizable processes

Summary The spectral domain of harmonizable processes is studied and a criterion for its completeness is obtained. It is shown that even for periodically correlated processes the spectral domain need not be complete.This work was funded in part by Office of Naval Research grant N00014-89-J-1824 and in part by US Army Research Office grant DAAL 03-91-G-0238. Part of these results has been presented at the May 1993 AMS meeting in DeKalb; ref. nr. 882-28-69     

The superconducting vibrating reed with pinned flux lines

A reed performing flexural vibrations in a longitudinal magnetic field may be used to measure pinning and viscose motion of the flux lines in type-II superconductors. As a first step we determine the vibration modes and resonance frequencies of a reed containing rigidly pinned flux lines and thus behaving dynamically like an ideal diamagnet.     

A new approach to spin & statistics

We give an algebraic proof of the spin-statistics connection for the parabosonic and parafermionic quantum topological charges of a theory of local observables with a modular P₁ CT-symmetry. The argument avoids the use of the spinor calculus and also works in 1 + 2 dimensions. It is expected to be a progress towards a general spin-statistics theorem including also (1 + 2)-dimensional theories with braid group statistics.     

High-temperature dynamics of the anisotropic spin-1/2 square lattice Heisenberg model studied by moment methods

The spin dynamics of the anisotropic spin-1/2 nearest-neighbour Heisenberg model (XYZ model) on a plane square lattice is studied at infinite temperature. Low-order coefficients of the short-time expansions for spin-spin correlation functions are calculated. The necessary commutator algebra may be performed by a computer. The series obtained for the spin correlation function are the longest ones available up to now. The series coefficients are used to construct rigorous upper and lower bounds to autocorrelation functions and near-neighbour correlation functions.