Non-perturbative interactions in string theory

New non-perturbative interactions in the effective action of two dimensional string theory are described. These interactions are due to ``stringy" instantonsComment: 6 pages, double coulumn Latex, 3 figures not included available as eps files on request, UPR-524

Non-Perturbative Effects in 2-D String Theory or Beyond the Liouville Wall

We discuss continuous and discrete sectors in the collective field theory of $d=1$ matrix models. A canonical Lorentz invariant field theory extension of collective field theory is presented and its classical solutions in Euclidean and Minkowski space are found. We show that the discrete, low density, sector of collective field theory includes single eigenvalue Euclidean instantons which tunnel between different vacua of the extended theory. We further show that these ``stringy" instantons induce non-perturbative effective operators of strength $e^{-{1\over g}}$ in the extended theory. The relationship of the world sheet description of string theory and Liouville theory to the effective space-time theory is explained. We also comment on the role of the discrete, low density, sector of collective field theory in that framework.Comment: 44 pages, 9 figures available as eps files on reques

The Strength of Non-Perturbative Effects in Matrix Models and String Effective Lagrangians

We present a summary of the results of an explicit calculation of the strength of non-perturbative interactions in matrix models and string effective Lagrangians. These interactions are induced by single eigenvalue instantons in the $d=1$ bosonic matrix model. A well defined approximation scheme is used to obtain induced operators whose exact form we exhibit. We briefly discuss the possibility that similar instantons in a supersymmetric version of the theory may break supersymmetry dynamically.Comment: Latex document, 17 pages, preprint CERN-TH.7356/94, UPR-620

Supersymmetric Field Theory from Supermatrix Models

We show that the continuum limit of one-dimensional N=2 supersymmetric matrix models can be described by a two-dimensional interacting field theory of a massless boson and two chiral fermions. We interpret this field theory as a two-dimensional N=1 supersymmetric theory of two chiral superfields, in which one of the chiral superfields has a non-trivial vacuum expectation value.Comment: Latex document, 11 pages, preprint CERN-TH.7353/94, UPR-621

Non-Equilibrium Phase Transitions and Domain Walls

Non-equilibrium phase transitions of a scalar field in an expanding spacetime are discussed. These transitions are shown to lead, for appropriate potential energy functions, to a biased choice of vacuum structure which can be analytically described using percolation theory. The initial domain wall networks, which form between different vacua, are evolved in time by computer simulation and their behavior analyzed. It is shown that, unlike systems in thermal equilibrium, domain walls formed in biased systems persist for only a short time before decaying exponentially away. This result opens the door to a re-analysis of domain walls in cosmology.Comment: uu-encoded postscript file. To appear in proceedings of PASCOS 95, 15 page

Standard Model bundles of the heterotic string

We show how to construct supersymmetric three-generation models with gauge group and matter content of the Standard Model in the framework of non-simply-connected elliptically fibered Calabi-Yau manifolds Z. The elliptic fibration on a cover Calabi-Yau, where the model has 6 generations of SU(5) and the bundle is given via the spectral cover description, has a second section leading to the needed free involution. The relevant involution on the defining spectral data of the bundle is identified for a general Calabi-Yau of this type and invariant bundles are generally constructible.Comment: 23 pp; minor remarks adde

The Background Field Method for N = 2 Super Yang-Mills Theories in Harmonic Superspace

The background field method for N=2 super Yang-Mills theories in harmonic superspace is developed. The ghost structure of the theory is investigated. It is shown that the ghosts include two fermionic real omega-hypermultiplets (Faddeev-Popov ghosts) and one bosonic real omega-hypermultiplet (Nielsen-Kallosh ghost), all in the adjoint representation of the gauge group. The one-loop effective action is analysed in detail and it is found that its structure is determined only by the ghost corrections in the pure super Yang-Mills theory. As applied to the case of N=4 super Yang-Mills theory, realized in terms of N=2 superfields, the latter result leads to the remarkable conclusion that the one-loop effective action of the theory does not contain quantum corrections depending on the N=2 gauge superfield only. We show that the leading low-energy contribution to the one-loop effective action in the N=2 SU(2) super Yang-Mills theory coincides with Seiberg's perturbative holomorphic effective action.Comment: 17 pages, Late