S. A. Kivelson, E. Fradkin, V. J. Emery Dept. of Physics, U.C.L.A., Los Angeles, CA 90095, Dept. of Physics, University of Illinois, Urbana, IL 61801-3080, and Brookhaven National Laboratory, Upton NY 11973-5000 (February 1, 2008) The character of the ground state of an antiferromagnetic insulator is fundamentally altered upon addition of even a small amount of charge. The added charges agglome...

Gauge theories have been a corner stone of the description of the world at the level of fundamental particles. The Lagrangian or the action describing the corresponding interactions is invariant under certain gauge transformations and contains the dependence on a covariant gauge parameter. This symmetry is reflected in terms of the Ward-Green-Takahashi (or the Slavnov-Taylor) identities (WGTI) ...

Before going into the subject of this talk, I would like to describe some concrete exercises done by Claude and I which represent a very small portion of the numerous discussions we had, mostly by exchange of letters. We happened to be both guests of the CERN theory division during the academic year 19721973. The perturbative renormalization of gauge theories was still a hot subject, and, where...

An interpretation of spacelike singularities in string theory uses target space duality to relate the collapsing Schwarzschild geometry near the singularity to an inflationary cosmology in dual variables. An appealing picture thus results whereby gravitational collapse seeds the formation of a new universe. PACS numbers: 04.70.-s, 11.25.-w String theory is strongly believed to solve the short-d...