Jacob Leedom
Non-perturbative effects in string theory, such as D-branes, play an essential role in our current understanding of both quantum gravity and string-based models of the universe. While D-branes are prevalent in the Type I and II theories, they appear absent in the two heterotic theories. This presents a puzzle, as a resurgence argument by S. Shenker suggests that brane-like objects should be present in all closed string theories. In this talk I will propose a resolution to this puzzle by describing the origin of certain non-perturbative contributions to higher-derivative terms in the 10d SO(32) heterotic action. These effects are intimately related with open heterotic strings, whose existence hinges on a non-trivial interplay between worldsheet and spacetime degrees of freedom.