A Chiral SU(N)SU(N) Gauge Theory and its Non-Chiral Spin(8)Spin(8) Dual

We study supersymmetric $SU(N-4)$ gauge theories with a symmetric tensor and $N$ antifundamental representations. The theory with $W=0$ has a dual description in terms of a non-chiral $Spin(8)$ theory with one spinor and $N$ vectors. This duality flows to the $SO(N)$ duality of Seiberg and to a duality proposed by one of us. It also flows to dualities for a number of $Spin(m)$ theories, $m\le 8$. For $N=6$, when an ${\cal N}=2$ SUSY superpotential is added, the singularities of Seiberg and Witten are recovered. For $N\le 6$, a mass for the spinor generates the branches of $SO(8)$ theories found by Intriligator and Seiberg. Other phenomena include a classical constraint mapped to an anomaly equation under duality and an intricate consistency check on the renormalization group flow.Comment: 13 pages, uses harvma

Finite Theories and Marginal Operators on the Brane

We show how to use D and NS fivebranes in Type IIB superstring theory to construct large classes of finite N=1 supersymmetric four dimensional field theories. In this construction, the beta functions of the theories are directly related to the bending of branes; in finite theories the branes are not bent, and vice versa. Many of these theories have multiple dimensionless couplings. A group of duality transformations acts on the space of dimensionless couplings; for a large subclass of models, this group always includes an overall SL(2,\ZZ) invariance. In addition, we find even larger classes of theories which, although not finite, also have one or more marginal operators.Comment: 32 pages, 13 figures, uses revte

The Higgs as a Portal to Plasmon-like Unparticle Excitations

A renormalizable coupling between the Higgs and a scalar unparticle operator O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry breaking, an infrared divergent vacuum expectation value for O_U. Such IR divergence should be tamed before any phenomenological implications of the Higgs-unparticle interplay can be drawn. In this paper we present a novel mechanism to cure that IR divergence through (scale-invariant) unparticle self-interactions, which has properties qualitatively different from the mechanism considered previously. Besides finding a mass gap in the unparticle continuum we also find an unparticle pole reminiscent of a plasmon resonance. Such unparticle features could be explored experimentally through their mixing with the Higgs boson.Comment: 12 LaTeX pages, 2 figure

Singe Top Production at LEP 200

We present exact tree level cross sections for the single top production process $e^- e^+ \rightarrow e^- \bar{\nu}_e t \bar{b}$ at LEP~200. The results reproduce roughly those obtained earlier by using the equivalent real photon approximation and we confirm the observation that detecting a top heavier than half the c.m.~energy is not feasible at LEP~200. The calculation has been performed by a new automatic Feynman amplitude generator MadGraph which produces HELAS code for the helicity amplitudes.Comment: 7 pages, 4 postscript figure