Precise estimates of presence probabilities in the branching random walk

In the subcritical speed area of a supercritical branching random walk, we prove that when the number of generations grows the probability of presence is asymptotically proportional to the corresponding expectation as in a subcritical Galton-Watson process. This improves a known result on the logarithm of this probability. The basic tools are a discrete version of the Feynman-Kac representation and large deviations.