The quantum period of a variety
is a generating function for certain Gromov–Witten invariants of
which
plays an important role in mirror symmetry. We compute the quantum periods of all
–dimensional
Fano manifolds. In particular we show that
–dimensional
Fano manifolds with very ample anticanonical bundle have mirrors given by a
collection of Laurent polynomials called Minkowski polynomials. This was
conjectured in joint work with Golyshev. It suggests a new approach to the
classification of Fano manifolds: by proving an appropriate mirror theorem and then
classifying Fano mirrors.
Our methods are likely to be of independent interest. We rework the Mori–Mukai classification
of
–dimensional
Fano manifolds, showing that each of them can be expressed as the zero
locus of a section of a homogeneous vector bundle over a GIT quotient
, where
is a product of
groups of the form
and
is a
representation of
.
When
, this expresses
the Fano
–fold
as a toric complete intersection; in the remaining cases, it expresses the Fano
–fold
as a tautological subvariety of a Grassmannian, partial flag manifold, or
projective bundle thereon. We then compute the quantum periods using the
quantum Lefschetz hyperplane theorem of Coates and Givental and the
abelian/non-abelian correspondence of Bertram, Ciocan-Fontanine, Kim and
Sabbah.
Faculty of Mathematics and
Laboratory of Algebraic Geometry
National Research University Higher School of Economics
7 Vavilova str.
Moscow
117312
Russia