  The Rees product of partially ordered sets was introduced by Bj\"orner and
Welker. Using the theory of lexicographic shellability, Linusson, Shareshian
and Wachs proved formulas, of significance in the theory of gamma-positivity,
for the dimension of the homology of the Rees product of a graded poset $P$
with a certain $t$-analogue of the chain of the same length as $P$. Equivariant
generalizations of these formulas are proven in this paper, when a group of
automorphisms acts on $P$, and are applied to establish the Schur
gamma-positivity of certain symmetric functions arising in algebraic and
geometric combinatorics.
