"Light from chaos" in two dimensions

We perform a Monte-Carlo study of the lattice two-dimensional gauged XY-model. Our results confirm the strong-coupling expansion arguments that for sufficiently small values of the spin-spin coupling the ``gauge symmetry breaking" terms decouple and the long-distance physics is that of the unbroken pure gauge theory. We find no evidence for the existence, conjectured earlier, of massless states near a critical value of the spin-spin coupling. We comment on recent remarks in the literature on the use of gauged XY-models in proposed constructions of chiral lattice gauge theories.Comment: 6 pages, 7 figure

Chiral Lattice Gauge Theories and The Strong Coupling Dynamics of a Yukawa-Higgs Model with Ginsparg-Wilson Fermions

The Yukawa-Higgs/Ginsparg-Wilson-fermion construction of chiral lattice gauge theories described in hep-lat/0605003 uses exact lattice chirality to decouple the massless chiral fermions from a mirror sector, whose strong dynamics is conjectured to give cutoff-scale mass to the mirror fermions without breaking the chiral gauge symmetry. In this paper, we study the mirror sector dynamics of a two-dimensional chiral gauge theory in the limitof strong Yukawa and vanishing gauge couplings, in which case it reduces to an XY model coupled to Ginsparg-Wilson fermions. For the mirror fermions to acquire cutoff-scale mass it is believed to be important that the XY model remain in its "high temperature" phase, where there is no algebraic ordering--a conjecture supported by the results of our work. We use analytic and Monte-Carlo methods with dynamical fermions to study the scalar and fermion susceptibilities, and the mirror fermion spectrum. Our results provide convincing evidence that the strong dynamics does not "break" the chiral symmetry (more precisely, that the mirror fermions do not induce algebraic ordering in two-dimensions), and that the mirror fermions decouple from the infrared physics.Comment: 44 pages, 18 figures; v2: clarification of fermion operators, discussion of recent related work

Chiral Lattice Gauge Theories Via Mirror-Fermion Decoupling: A Mission (im)Possible?

This is a review of the status and outstanding issues in attempts to construct chiral lattice gauge theories by decoupling the mirror fermions from a vectorlike theory. In the first half, we explain why studying nonperturbative chiral gauge dynamics may be of interest, enumerate the problems that a lattice formulation of chiral gauge theories must overcome, and briefly review our current knowledge. We then discuss the motivation and idea of mirror-fermion decoupling and illustrate the desired features of the decoupling dynamics by a simple solvable toy model. The role of exact chiral symmetries and matching of 't Hooft anomalies on the lattice is also explained. The second, more technical, half of the article is devoted to a discussion of the known and unknown features of mirror-decoupling dynamics formulated with Ginsparg-Wilson fermions. We end by pointing out possible directions for future studies.Comment: 53 pp; 6 figs; added table of contents, references, fixed typo

Dynamical Supersymmetry Breaking

I review the motivation for dynamical supersymmetry breaking, the various mechanisms which have been discovered, and the prospects for model building.Comment: 5 pages. invited talk given at SUSY97, May27-31, 1997, University of Pennsylvani

AdS/CFT and large-N volume independence

We study the Eguchi-Kawai reduction in the strong-coupling domain of gauge theories via the gravity dual of N=4 super-Yang-Mills on R^3xS^1. We show that D-branes geometrize volume independence in the center-symmetric vacuum and give supergravity predictions for the range of validity of reduced large-N models at strong coupling.Comment: 4 pages, 2 figures; references and comments adde

Conformal windows of SP(2N) and SO(N) gauge theories from topological excitations on R3 * S1

We derive an estimate of the lower boundary of the conformal window of SP(2N) and SO(N) gauge theories with fermionic matter in several different representations. We calculate the index of topological excitations for these groups on the manifold R3 * S1, from which we deduce the scale of the generation of the mass gap of the theory. This is then used to approximate the critical value of the number of species for the onset of conformality on R4. We also provide a detailed comparison with other estimates of the conformal window.Comment: 23 pages, 4 figures, 7 tables; updated results, added comparisons, references adde

Anomalous U(1)_A and Electroweak Symmetry Breaking

We suggest a new mechanism for electroweak symmetry breaking in the supersymmetric Standard Model. Our suggestion is based on the presence of an anomalous U(1)_A gauge symmetry, which naturally arises in the four dimensional superstring theory, and heavily relies on the value of the corresponding Fayet-Illiopoulos \xi-term.Comment: Latex, 11 pages, discussions and references adde