Effect of Noise on Front Propagation in Reaction-Diffusion equations of KPP type
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We consider reaction-diffusion equations of KPP type in one spatial dimension, perturbed by a Fisher-Wright white noise, under the assumption of uniqueness in distribution. Examples include the randomly perturbed Fisher-KPP equations $ \partial_t u = \partial_x^2 u + u(1-u) + ε\sqrt{u(1-u)}\dot W, $ and $ \partial_t u = \partial_x^2 u + u(1-u) + ε\sqrt{u}\dot W, $ where $\dot W= \dot W(t,x)$ is a space-time white noise.
We prove the Brunet-Derrida conjecture that the speed of traveling fronts is asymptotically $ 2-π^2 |\log ε^2|^{-2} $ up to a factor of order $ (\log|\logε|)|\logε|^{-3}$.