Multi-String Theories, Massive Gravity and the AdS/CFT Correspondence

Infrared modifications of gravity have been proposed over the years as potentially useful phenomenological models. Massive (multi)-gravity is an interesting class of such theories. The true nature and the ultimate consistency of many of these models remains, however, unclear as one is frequently faced with important problems, e.g. classical instabilities and strong coupling problems which are hard to resolve without a known UV completion of the theory. In this note, we review a recent attempt to study some of these well known problems with the use of the AdS/CFT correspondence. In this context, products of largeN conformal field theories coupled by multi-trace interactions in diverse dimensions are used to define quantum multi-gravity (multi-string/M theory) on a union of (asymptotically) AdS spaces. One-loop effects generate a small O(1/N) mass for the gravitons and provide non-trivial examples of massive multi-graviton theories.