We invert the period map defined by the second structure connection of
quantum cohomology of P2. For small quantum cohomology the inverse
is given explicitly in terms of the Eisenstein series E4 and E6, while
for big quantum cohomology the inverse is determined perturbatively as a Taylor
series expansion whose coefficients are quasi-modular forms.Comment: 58 pages. Typos fixed. The previous version was extended in the
following way: we proved the Laplace transform version of the
Γ-conjecture for P2, worked out the structure of a Schwarz
triangular map, and added an appendix explaining the relation to vertex
algebras and W-constraints. Version accepted in Adv. in Mat