Bounds on the speed and on regeneration times for certain processes on regular trees

Abstract

We develop a technique that provides a lower bound on the speed of transient random walk in a random environment on regular trees. A refinement of this technique yields upper bounds on the first regeneration level and regeneration time. In particular, a lower and upper bound on the covariance in the annealed invariance principle follows. We emphasize the fact that our methods are general and also apply in the case of once-reinforced random walk. Durrett, Kesten and Limic [Probab. Theory Related Fields. 122 (2002) 567–592] prove an upper bound of the form b/(b+δ) for the speed on the b-ary tree, where δ is the reinforcement parameter. For δ>1 we provide a lower bound of the form γ²b/(b+δ), where γ is the survival probability of an associated branching process.