Supersymmetry and the Geometry of Taub-NUT

The supersymmetric extension of Taub-NUT space admits 4 standard supersymmetries plus several additional non-standard ones. The geometrical origin of these symmetries is traced. The result has applications to fermion modes in gravitational instantons as well as in long-range monopole dynamics.Comment: 9 pages, NIKHEF-H/94-2

Domain boundaries, Goldstone bosons and gravitational waves

The dynamical behaviour of domain boundaries between different realizations of the vacuum of scalar fields with spontaneously broken phases is investigated. They correspond to zero-modes of the Goldstone fields, moving with the speed of light, and turn out to be accompanied by strongly oscillating gravitational fields. In certain space-time topologies this leads to a quantization condition for the symmetry breaking scale in terms of the Planck mass.Comment: 6 page

Propagators and Path Integrals

Path-integral expressions for one-particle propagators in scalar and fermionic field theories are derived, for arbitrary mass. This establishes a direct connection between field theory and specific classical point-particle models. The role of world-line reparametrization invariance of the classical action and the implementation of the corresponding BRST-symmetry in the quantum theory are discussed. The presence of classical world-line supersymmetry is shown to lead to an unwanted doubling of states for massive spin-1/2 particles. The origin of this phenomenon is traced to a `hidden' topological fermionic excitation. A different formulation of the pseudo-classical mechanics using a bosonic representation of \gam_5 is shown to remove these extra states at the expense of losing manifest supersymmetry.Comment: 35 pages, latex, no figures, additional references; to be published in Nucl. Phys.