Theory HEP Seminar

Infinite Distance Limits and Factorization

John Stout

Harvard University

Continuous families of quantum theories often come equipped with a natural metric that defines a notion of distance between different theories. Two well-known examples are the moduli space metric in supersymmetric theories and the Zamolodchikov metric in conformal field theories. Intriguingly, infinite distance limits in these metrics are observed to enjoy a number of seemingly universal properties: they have “logarithmic” metric singularities, are always associated with weak-coupling limits, and---in quantum gravitational theories---are tied to the appearance of a tower of exponentially light fields. The goal of this talk is to explain why these features are universal. I'll explain how these more familiar metrics are examples of a more general, albeit unique, metric called the information metric that can be defined on any continuous family of theories. Then I'll explain how the first two of these universal properties are consequences of unitarity and why these limits necessarily have such dramatic behavior in quantum gravitational theories.