Branching random walk conditioned on large martingale limit

We consider a branching random walk in the non-boundary case where the additive martingale Wₙ converges a. s. and in mean to some non-degenerate limit W_. We first establish the joint tail distribution of W_ and the global minimum of this branching random walk. Next, conditioned on the event that the minimum is atypically small or conditioned on very large W_, we study the branching random walk viewed from the minimum and obtain the convergence in law in the vague sense. As a byproduct, we also get the right tail of the limit of derivative martingale.