We construct creation and annihilation operators for deformed harmonic oscillators with minimal length uncertainty relations. We discuss a possible generalization to a large class of deformations of cannonical commutation relations. We also discuss dynamical symmetry of noncommutative harmonic oscillator.

A three-channel, multi-resonance, unitary model developed in 1995 is used to determine the πN → ηN and ηN → ηN amplitudes by re-analyzing the available data on πN elastic scattering and the weighted data for the πN → ηN total and differential cross sections. The input πN elastic scattering amplitude in the S11 channel has been improved, following suggestions of G. Höhler. Our new result of ηN scattering length, aηN = (0.717±0.030)+i · (0.263±0.025) fm, suggests that the ηd system is unbound or loosely bound.

We analyze ill-defined pinch singularities characteristic of out of equilibrium thermal field theories. We identify two mechanisms that eliminate pinching even at the single self-energy insertion approximation to the propagator: the first is based on the vanishing of phase space at the singular point ͑threshold effect͒. It is effective in QED with a massive electron and a massless photon. In massless QCD, this mechanism fails, but the pinches cancel owing to the second mechanism, i.e., owing to the spinor or tensor structure of the single self-energy insertion contribution to the propagator. The constraints imposed on distribution functions are very reasonable. ͓S0556-2821͑99͒02812-X͔

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