Weakly self-avoiding walk in a Pareto-distributed random potential

We investigate a model of continuous-time simple random walk paths in Zd undergoing two competing interactions: an attractive one toward the large values of a random potential and a self-repellent one in the spirit of the well-known weakly self-avoiding random walk. We take the potential to be i.i.d. Pareto-distributed with parameter α>d, and we tune the strength of the interactions in such a way that they both contribute on the same scale as t→∞. Our main results are: (1) the identification of the logarithmic asymptotics of the partition function of the model in terms of a random variational formula and (2) the identification of the path behaviour that gives the overwhelming contribution to the partition function for α>2d: the random-walk path follows an optimal trajectory that visits each of a finite number of random lattice sites for a positive random fraction of time. We prove a law of large numbers for this behaviour, that is, that all other path behaviours give strictly less contribution to the partition function. The joint distribution of the variational problem and of the optimal path can be expressed in terms of a limiting Poisson point process arising by a rescaling of the random potential. The latter convergence is in distribution and is in the spirit of a standard extreme-value setting for a rescaling of an i.i.d. potential in large boxes, like in (Ann. Probab. 37 (2009) 347–392).