Quasi-critical fluctuations for 2D directed polymers

We study the 2d directed polymer in random environment in a novel quasi-critical regime, which interpolates between the much studied sub-critical and critical regimes. We prove Edwards–Wilkinson fluctuations throughout the quasi-critical regime, showing that the diffusively rescaled partition functions are asymptotically Gaussian. We deduce a corresponding result for the critical 2d Stochastic Heat Flow. A key challenge is the lack of hypercontractivity, which we overcome deriving new moment estimates.