Screening Effect Due to Heavy Lower Tails on One-dimensional Parabolic Anderson Model

We consider the large-time behavior of the solution u:[0,∞)×Z→[0,∞)">u:[0,∞)×Z→[0,∞) to the parabolic Anderson problem ∂_tu=κΔu+ξu with initial data u(0, ·)=1 and non-positive finite i.i.d. potentials (ξ(z))z∈Z">(ξ(z))z∈Z. Unlike in dimensions d≥2, the almost-sure decay rate of u(t, 0) as t→∞ is not determined solely by the upper tails of ξ(0); too heavy lower tails of ξ(0) accelerate the decay. The interpretation is that sites x with large negative ξ(x) hamper the mass flow and hence screen off the influence of more favorable regions of the potential. The phenomenon is unique to d=1. The result answers an open question from our previous study [BK00] of this model in general dimension.