Author(s): Gabriela Barenboim, Aurora Ireland, and Albert Stebbins We present observational constraints on large-scale white noise (LSWN) in the cosmic density field, a phenomenon predicted to arise from nonlinear mode coupling during cosmological evolution. Building on the theoretical framework of our companion paper, where we demonstrated that nonlinearities inev… [Phys. Rev. Lett. 137, 081003] Published Tue Aug 18, 2026