Density of States and Tachyons in Open and Closed String Theory

In this note we reexamine the possibility of constructing stable non-supersymmetric theories that exhibit an exponential density of states. For weakly coupled closed strings there is a general theorem, according to which stable theories with an exponential density of states must exhibit an almost exact cancellation of spacetime bosons and fermions (not necessarily level by level). We extend this result to open strings by showing that if the above cancellation between bosons and fermions does not occur, the open strings do not decouple from a closed string tachyon even in the NCOS scaling limit. We conclude with a brief comment on the proposed generalization of the AdS/CFT correspondence to non-supersymmetric theories.Comment: 11 pages, harvmac, v2: improved discussion, references added, v3: version published in JHE

(Multi)Matrix Models and Interacting Clones of Liouville Gravity

Large-N matrix models coupled via multitrace operators are used to define, via appropriate double-scaling limits, solvable models of interacting multi-string theories. It is shown that although such theories are non-local at the world-sheet level they have a simple description of the spacetime physics. Such theories share the main characteristics of similarly coupled higher-dimensional CFTs. An interpretation has been given in the past of similar continuum limits in terms of Liouville interactions that violate the Seiberg bound. We provide a novel interpretation of this relation which agrees with the current understanding of Liouville theory and analogous observations in the AdS/CFT correspondence.Comment: 45 pages, 4 figures; v2 references added, version to appear in JHE