Powers of positive polynomials and codings of Markov chains onto Bernoulli shifts

We give necessary and sufficient conditions for a Markov chain to factor onto a Bernoulli shift (i) as an eventual right-closing factor, (ii) by a right-closing factor map, (iii) by a one-to-one a.e. right-closing factor map, and (iv) by a regular isomorphism. We pass to the setting of polynomials in several variables to represent the Bernoulli shift by a nonnegative polynomial $p$ in several variables and the Markov chain by a matrix $A$ of such polynomials. The necessary and sufficient conditions for each of (i)-(iv) involve only an eigenvector $r$ of $A$ and basic invariants obtained from weights of periodic orbits. The characterizations of (ii)-(iv) are deduced from (i). We formulate (i) as a combinatorial problem, reducing it to certain state-splittings (partitions) of paths of length $n$. In terms of positive polynomial masses associated with paths, the aim then becomes the construction of partitions so that the masses of the paths in each partition element sum to a multiple of $p^n$, the multiple being prescribed by $r$. The construction, which we sketch, relies on a description of the terms of $p^n$ and on estimates of the relative sizes of the coefficients of $p^n$.