A Distance Conjecture for Branes

Abstract: We use branes to generalize the Distance Conjecture. We conjecture that in any infinite-distance limit in the moduli space of a $d$-dimensional quantum gravity theory, among the set of particle towers and fundamental branes with at most $p_\text{max}\leq d-2$ spacetime dimensions, at least one has mass/tension decreasing exponentially $T\sim \exp(-\alpha\Delta)$ with the moduli space distance $\Delta$ at a rate of at least $\alpha\geq 1/\sqrt{d-p_\text{max}-1}$. Since $p_\text{max}$ can vary, this represents multiple conditions, where the Sharpened Distance Conjecture is the $p_\text{max}=1$ case. This conjecture is a necessary condition imposed on higher-dimensional theories in order for the Sharpened Distance Conjecture to hold in lower-dimensional theories. We test our conjecture in theories with maximal and half-maximal supersymmetry in diverse dimensions, finding that it is satisfied and often saturated. In some cases where it is saturated -- most notably, heterotic string theory in 10 dimensions -- we argue that novel, low-tension non-supersymmetric branes must exist. We also identify patterns relating the rates at which various brane tensions vary in infinite-distance limits and relate these tensions to the species scale.