In this paper, we generalize the Givental theory for Frobenius manifolds and
cohomological field theories to flat F-manifolds and F-cohomological field
theories. In particular, we define a notion of Givental cone for flat
F-manifolds, and we provide a generalization of the Givental group as a matrix
loop group acting on them. We show that this action is transitive on semisimple
flat F-manifolds. We then extend this action to F-cohomological field theories
in all genera. We show that, given a semisimple flat F-manifold and a Givental
group element connecting it to the constant flat F-manifold at its origin, one
can construct a family of F-CohFTs in all genera, parameterized by a vector in
the associative algebra at the origin, whose genus $0$ part is the given flat
F-manifold. If the flat F-manifold is homogeneous, then the associated family
of F-CohFTs contains a subfamily of homogeneous F-CohFTs. However, unlike in
the case of Frobenius manifolds and CohFTs, these homogeneous F-CohFTs can have
different conformal dimensions, which are determined by the properties of a
certain metric associated to the flat F-manifold.
