A counterexample to the CFT convexity conjecture

Abstract

Motivated by the weak gravity conjecture, [Phys. Rev. D 104 (2021) 126005] conjectured that in any CFT, the minimal operator dimension at fixed charge is a convex function of the charge. In this letter we construct a counterexample to this convexity conjecture, which is a clockwork-like model with some modifications to make it a weakly-coupled CFT. We also discuss further possible applications of this model and some modified versions of the conjecture which are not ruled out by the counterexample.