We investigate the free energy of nearest-neighbor random walks on $\mathbb{ Z}^d$, endowed with a drift along the first axis and evolving in a nonnegative random potential given by i.i.d. random variables. Our main result concerns the ballistic regime in dimensions $d\geq4$, at which we show that quenched and annealed Lyapunov exponents are equal as soon as the strength of the potential is small enough.
Categories: math.PR math-ph math.MP