In this paper, we initiate the study of the Givental group action on
Cohomological Field Theories in terms of homotopical algebra. More precisely,
we show that the stabilisers of Topological Field Theories in genus 0
(respectively in genera 0 and 1) are in one-to-one correspondence with
commutative homotopy Batalin--Vilkovisky algebras (respectively wheeled
commutative homotopy BV-algebras).
This paper provides an explicit cofibrant resolution of the operad encoding
Batalin-Vilkovisky algebras. Thus it defines the notion of homotopy
Batalin-Vilkovisky algebras with the required homotopy properties.
To define this resolution we extend the theory of Koszul duality to operads
and properads that are defind by quadratic and linear relations. The operad
encoding Batalin-Vilkovisky algebras is shown to be Koszul in this sense. This
allows us to prove a Poincare-Birkhoff-Witt Theorem for such an operad and to
give an explicit small quasi-free resolution for it.