Stationary States of the One-Dimensional Discrete-Time Facilitated Symmetric Exclusion ProcessWe describe the extremal translation invariant stationary (ETIS) states of
the facilitated exclusion process on $\mathbb{Z}$. In this model all particles
on sites with one occupied and one empty neighbor jump at each integer time to
the empty neighbor site, and if two particles attempt to jump into the same
empty site we choose one randomly to succeed. The ETIS states are qualitatively
different for densities $ρ<1/2$, $ρ=1/2$, and $1/2<ρ<1$, but in each
density region we find states which may be grouped into families, each of which
is in natural correspondence with the set of all ergodic measures on
$\{0,1\}^{\mathbb{Z}}$. For $ρ<1/2$ there is one such family, containing all
the ergodic states in which the probability of two adjacent occupied sites is
zero. For $ρ=1/2$ there are two families, in which configurations translate
to the left and right, respectively, with constant speed 2. For the high
density case there is a continuum of families. We show that all ETIS states at
densities $ρ\le1/2$ belong to these families, and conjecture that also at
high density there are no other ETIS states. We also study the possible ETIS
states which might occur if the conjecture fails.
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