  In the approach to Gromov-Witten theory developed by Givental, genus-zero
Gromov-Witten invariants of a manifold X are encoded by a Lagrangian cone in a
certain infinite-dimensional symplectic vector space. We give a construction of
this cone, in the spirit of S^1-equivariant Floer theory, in terms of
S^1-equivariant Gromov-Witten theory of the product X \times P^1. This gives a
conceptual understanding of the "dilaton shift": a change-of-variables which
plays an essential role in Givental's theory.
