Transport Meeting

Fick’s law leads to acausal behavior by enforcing instantaneous response. The Maxwell-Cattaneo theory restores causality through a finite relaxation time, giving rise to a quasi-diffusive regime when this time becomes comparable to the diffusion timescale. Within the Schwinger–Keldysh effective field theory framework, we compute the real-time correlation functions of the causal theory at one loop. In both the underdamped and overdamped limits, we identify two universal scaling functions that govern the dynamics. This structure imposes deep constraints on correlation functions in quasi-diffusive systems and opens the door to precision studies of transport beyond the standard hydrodynam