In this paper, we consider a random walk and a random color scenery on Z. The
increments of the walk and the colors of the scenery are assumed to be i.i.d.
and to be independent of each other. We are interested in the random process of
colors seen by the walk in the course of time. Bad configurations for this
random process are the discontinuity points of the conditional probability
distribution for the color seen at time zero given the colors seen at all later
times. We focus on the case where the random walk has increments 0, +1 or -1
with probability epsilon, (1-epsilon)p and (1-epsilon)(1-p), respectively, with
p in [1/2,1] and epsilon in [0,1), and where the scenery assigns the color
black or white to the sites of Z with probability 1/2 each. We show that,
remarkably, the set of bad configurations exhibits a crossover: for epsilon=0
and p in (1/2,4/5) all configurations are bad, while for (p,epsilon) in an open
neighborhood of (1,0) all configurations are good. In addition, we show that
for epsilon=0 and p=1/2 both bad and good configurations exist. We conjecture
that for all epsilon in [0,1) the crossover value is unique and equals 4/5.
Finally, we suggest an approach to handle the seemingly more difficult case
where epsilon>0 and p in [1/2,4/5), which will be pursued in future work.Comment: Published in at http://dx.doi.org/10.1214/11-AOP664 the Annals of
Probability (http://www.imstat.org/aop/) by the Institute of Mathematical
Statistics (http://www.imstat.org