  In a system with one conserved charge the charge diffusion is modified by
non-linear self-interactions within an effective field theory (EFT) of
diffusive fluctuations. We include the slowest ultraviolet (UV) mode,
constructing a UV-regulated EFT. The relaxation time of this UV mode is
protected from renormalization, as supported by experimental data in a bad
metal system. Furthermore, the retarded density-density Green's function
acquires four branch points, eventually increasing the range of applicability.
We discuss the fate of long-time-tails as well as implications for the quark
gluon plasma.
