Specializations of MacMahon symmetric functions and the polynomial algebra

A MacMahon symmetric function is a formal power series in a finite number of alphabets that is invariant under the diagonal action of the symmetric group. We use a combinatorial construction of the different bases of the vector space of MacMahon symmetric functions found by the author to obtain their image under the principal specialization: the powers, rising and falling factorials. Then, we compute the connection coefficients of the different polynomial bases in a combinatorial way.