Random walk weakly attracted to a wall

Abstract

We consider a random walk X_n in Z_+, starting at X_0=x>= 0, with transition probabilities P(X_{n+1}=X_n+1|X_n=y>=1)=1/2-δ/(4y+2δ) P(X_{n+1}=X_n+1|X_n=y>=1)=1/2+δ/(4y+2δ) and X_{n+1}=1 whenever X_n=0. We prove that the expectation value of X_n behaves like n^{1-(δ/2)} as n goes to infinity when δis in the range (1,2). The proof is based upon the Karlin-McGregor spectral representation, which is made explicit for this random walk.

Replacement with minor changes and additions in bibliography. Same abstract, in plain text rather than TeX