We prove that the reduced
Hochschild homology of a commutative DG Frobenius algebra has the natural
structure of a Batalin–Vilkovisky coalgebra, and the reduced cyclic homology
has the natural structure of a gravity coalgebra. As an application, this
gives an algebraic model for a Batalin–Vilkovisky coalgebra structure on
the reduced homology of the free loop space of a simply connected closed
oriented manifold, and a gravity coalgebra structure on the reduced equivariant
homology.