Convolution Integrals and a Mirror Theorem from Toric Fiber Geometry ()
1. Introduction
1.1. Formulations
Our main results are formulated in terms of the formal series
called the genus-0 descendant potential of M, where M is respectively
(as in the Abstract), the base of the toric fibration E, or a suitable divisor of the base. The ingredients of the series are defined in the generality of almost-Kähler manifolds M, as follows. The spaces
are moduli spaces of (equivalence classes of) degree-D stable maps into M of genus-0 (possibly nodal) compact connected holomorphic curves with n marked points. Two such stable maps
and
are equivalent if there is a holomorphic automorphism
mapping marked points to marked points and preserving the ordering, such that
. For a stable map
, the degree-D condition reads
.
Then,
denotes the virtual fundamental class of
. The ingredient
is the 1st Chern class of the universal cotangent line bundle over
whose fiber at a stable map
is the cotangent line along the stable map at the a-th marked point. The maps
evaluate the stable maps at the a-th marked points.
The Mori cone MC of M is the semigroup in
generated by classes representable by compact holomorphic curves. Then
is the element in the Novikov ring (the power-series completion of the semigroup algebra of the Mori cone) representing the degree
. Lastly,
are arbitrary cohomology classes of M with coefficients in a suitable ground ring
(for now, the Novikov ring with rational coefficients
).
It is convenient for this purpose to choose a basis
of
, and extend to a basis of
. Then, the dual basis can be thought of in terms of a corresponding basis of curve classes, and its extension to
. Define Novikov’s variables
; these record, for the exponent, the pairing of
on a curve class
. Equivalently, the variable
records the coefficients of the curve classes
along the dual basis vector to
, in the dual basis expansion of
.
1.2. Toric Fibrations
Let
be an integer matrix, and consider the action of
on the Hermitian space
that, for each
, multiplies the coordinate
by
. Let
be the map given by
.
If the moment map
has a regular value
, then
is a symplectic manifold. This construction is called symplectic reduction. The space
is also denoted by
, and is equipped with a canonical symplectic form, call it
, induced by the standard symplectic form on
. All complex line bundles over B may be assumed to have the unitary circle
as structure group, as they are induced by pullback from the tautological line bundle over
. Given complex line bundles
over B, it follows that
is the structure group of the vector bundle
. Thus, the fiberwise symplectic reduction of
is well-defined giving the toric fibration
. The ith coordinate
on the torus
defines a circle bundle over E for which the expression
defines connection 1-forms in the bundle. Denote by
the first Chern class of the ith circle bundle over E, and
its restriction to a fiber. The
classes are of Hodge
-type by the Fubini-Study construction, though they need not be Kähler classes1. Let
be any
-fixed point of
, and
representing the
-equivalence class
. The orbits
and
are then identical. It follows that there is some coordinate subspace
with coordinates
, containing p, such that none of the coordinates
vanishes. It will be convenient to think of the
-fixed strata
of E in terms of the corresponding indices
. For each
, the restriction of
to a fiber is Poincaré dual to the jth coordinate divisor
. Define
for
. The expressions for the pullbacks
in terms of
may be summarized by the equations
.
Set
. All bundles introduced thus far are T-equivariant, so their Chern classes may be assumed to take values in the T-equivariant cohomology group
, or
, with coefficient ring
.
1.3. The Cone
Associated to the genus-0 Gromov-Witten theory of M is a Lagrangian cone
in a symplectic loop space
[1] [2] [3]. The space
is a module over the ground ring
. Pending further completions,
consists of Laurent series in 1/z with coefficients in
, completed so that
consists of elements of
at each order in Novikov’s variables, and
. Identify each
with the domain variables
of
by the dilaton shift convention
. Take the ring of coefficients for Novikov’s variables to be the (super-commutative) power series ring (with coefficients in the field of fractions
, in all of our applications) in the formal coordinates along
, and require the variables
to vanish when Novikov’s variables and formal coordinates along
are all set to zero. This gives a Novikov ring
that is consistent with the formula for
in our Main Theorem.
Let
be a basis of
and
the Poincaré-dual basis. Consider the symplectic manifold
with standard symplectic form
. It is symplectomorphic to
with symplectic form
,
where
is the Poincaré pairing.
Let us implement this symplectomorphism via the map
.
Consider the graph of the differential of
, which is a Lagrangian submanifold in
. From there, we arrive at
by rigid translation in the direction of the dilaton shift. Thus
is also a Lagrangian submanifold. Henceforth we consider
as a submanifold of
. The work of Coates-Givental [1] , establishes that
is a (Lagrangian) cone as a formal Lagrangian section of
near
; that is,
.
In particular, each tangent space is preserved by multiplication by z.
It may be that
contains (as a limit point) the
-coordinate origin (0, 0), as a special case of Getzler’s [4] , Givental’s [5] solution, and its geometric formulation [1] , of Eguchi-Xiong’s, Dubrovin’s
-jet conjecture, as follows.
The shift of the formal variable
in the z-(or
-) direction appears to be well-understood, so perhaps formality of the geometry (to guarantee convergence of
) in the z-direction need not be assumed. This existence (via convergence) of the “vertex” or the “limiting vertex” of the cone gives an intuitive way to think about the introductory material; however, the author has not studied this convergence sufficiently. In our main theorem, the domain variable
is consistent with the setting of formal geometry.
The Lagrangian cone
of the T-equivariant genus-0 Gromov-Witten theory of
lies in the corresponding symplectic loop space
as above. A point in the cone can be written as
,
where
denotes the virtual push-forward by the evaluation map
, and
is an arbitrary element of
with coefficients
. Define the J-function to be the restriction of
to values
and to
for all
. For each
there is a unique
such that
.
This property of the set of all tangent spaces2 of
to be in 1-1 correspondence with the set H, which is a finite-dimensional
-module, is called overruled. For each
and for each open set
, the J-function generates a module over the algebra
of differential operators as follows,
where
is the unital, associative, (super-)commutative quantum cup product. Additionally, the J-function satisfies the string and divisor equations:
,
and
respectively. The graded homogeneity, defined by degrees of formal variables, makes the quantum cup product a degree 0 operation, the J-function graded homogeneous of degree 1, and z of degree 1.
1.4. Twisted Lagrangian Cones
The forgetful maps
induce the K-theoretic push-forward maps
. Let
be a complex vector bundle over M. The evaluation maps
induce the (virtual-) bundles
, in terms of which the (virtual-) virtual bundles
are defined. The fiber of
over a stable map
is
.
Given a characteristic class
, define the twisted Poincaré pairing
.
A point in the
-twisted cone can be written as
.
The overruled Lagrangian cone
in the
-twisted genus-0 Gromov-Witten theory of M lies in the symplectic loop space
, where
is an element of
with arbitrary coefficients
. The examples we will consider are:
Example 1.4.1.
, and
is a convex line bundle; i.e.,
; or equivalently,
for all genus-0 stable maps
to M.
Example 1.4.2.
, and
is a complex vector bundle with a hamiltonian T-action that decomposes
into a direct sum of complex line bundles, each of which carries a non-trivial T-action.
1.5. Torus Action on
The manifold
may be described as the result of surgery on E, along the divisor
of the T-fixed section
, as we now recall. The notation
, and
recall the detailed local geometry near the exceptional divisor
. Define a map from a tubular neighborhood of the
bundle over the projective space bundle
over
to a tubular neighborhood of
over
as follows. Fiberwise, it is described by the projection map
This construction holds in the generality3 of complex manifolds and submanifolds, respectively, where
is replaced by
(normal bundle to the submanifold within the ambient manifold). The map
collapses the projective space fibers
fiberwise over
. The map
is the identity map away from the points
above, and thus extends over the entire gluing space
. This map identifies T-equivariantly the complements of the 0-sections of the total spaces of the preceding two vector bundles. Remove a tubular neighborhood of
from E, and replace it by a tubular neighborhood of the
bundle over
.
We will call the resulting manifold the projective-space (surgery, gluing, quotient) of E along
, the
quotient-space of E along
, the
quotient-space of E along
(Section 2.1), the
surgery-space of E along (or normal to)
. Henceforth, we denote this by
, for simplicity of notation.
1.6. Simplification: Toric Manifold
Let X be a compact symplectic toric manifold and let
be the maximal unitary torus, and let Y be a T-invariant submanifold of X. Then
is again a toric manifold. As explained in Section 1.5, though not in the generality needed here, the action of T on X induces an action of T on
. Thus, we may study T-equivariant genus-0 Gromov-Witten invariants of
, the
-quotient of X along (or normal to) Y directly, using fixed-point localization. All faces of the moment polytope of Y are faces of the moment polytope of X. The moment polytope of
admits a canonical inclusion into the moment polytope of X, for which all faces of the moment polytope of
are contained in faces of the corresponding same dimension of the moment polytope of X. Let
be the primitive integer normal vectors to the codimension one faces of the moment polytope of a toric manifold. Let
be a basis of the
-vector space
consisting of primitive integer vectors. The toric manifold is then recovered from symplectic reduction referred to the matrix
, whose row vectors are
. By a mirror theorem of Givental [6] and its extensions [7] , a particular family of points on the Lagrangian cone of the genus-0 Gromov-Witten theory of a toric manifold is given by an explicit formula4 in terms of
,
This project has its roots in the following instructive example. Let E be the total space of the projective bundle

described by symplectic reduction with respect to the matrix
Let
be the section of E that maps each point
to the point
in the fiber over x. When X is the toric bundle E and Y is
then a calculation gives
In particular,
This example provides a reference point for navigating the project. The matrix may be computed using Appendix A in [8] , which is itself a summary of literature [9] [10] [11] [12] on moment maps and aspects of toric manifolds. Namely, in the momentum polyhedron of a toric manifold, the 1-dim edge vectors leaving a vertex at a T-fixed point
are positive multiples of the elements of the set
. These latter are the weights of the T-action on the normal bundle to
in the toric manifold.
Apply this first to the original projective bundle
. Then compute the weights of the T-action on the normal bundles in
to the T-fixed points of the exceptional divisor. Finally, compute the normals to the codimension one faces of the momentum polyhedron of
. A basis of linear relations among them is given by the rows of the matrix.
However, in fact, our main theorem arises as a generalization of this example. Here we are using the toric mirror theorems [6] [7] [8] as a guide to the structure of genus-0 Gromov-Witten invariants more generally (following the initial proposals of A. Elezi and A. Givental). Elezi’s work focused on projective bundles [13]. In [14] , Givental proposed a toric bundles generalization of Elezi’s approach using toric mirror integral representations [6] [7]. This is an ingredient in [8] and in the present work.
1.7. Organization of the Text
We recall in Section 2.2 the Atiyah-Bott fixed-point localization Theorem which implies, in particular, that any element of
is uniquely determined by its restrictions to the T-fixed strata
of
. Points
on the overruled Lagrangian cone of the genus-0 T-equivariant Gromov-Witten theory of
are certain H-valued formal functions, which we study in terms of their restrictions
. As we recall [8] in Section 5, the
projection of each of the restrictions
consists of two types of terms. Namely, there are terms ii) that form simple poles expanded as
series about non-zero
-values of z. The remaining terms i) are polynomial in
at any given order in formal variables
. The organising principle of the text, formulated as Theorem 2, characterizes the Lagrangian cone of the genus-0 T-equivariant Gromov-Witten theory of
in terms of two conditions i) ii) on
. The condition ii) says that the residues of
at its simple poles at non-zero values of z are governed recursively with respect to
. The condition i) describes the remaining poles at
in terms of a certain twisted Lagrangian cone of the stratum
. The Main Theorem gives a family of points
whose restrictions satisfy the conditions of Theorem 2.
In Section 6 we verify condition ii) for the restrictions
directly, using their defining formulae. In Section 7, we verify condition i) using transformation laws [1] of Lagrangian cones with respect to the twisting construction from Section 1.4 and example 1.8 (expanding simple poles at non-zero values of z in non-negative powers of z). A new aspect of the present work relative to toric bundles is that ii) relates the series
that, according to condition i), lie in Lagrangian cones derived from genus-0 Gromov-Witten invariants of B and of
, respectively. The Quantum Lefschetz Theorem relates the Lagrangian cone associated to the genus-0 Gromov-Witten theory of A with that of B. If the push-forward
does not identify the Mori cone of
with that of B, the opposite relation describing the Lagrangian cone of B in terms of that of
is realised algebraically by the Birkhoff factorization procedure and dividing by powers of z. Division by z does not preserve the Lagrangian cone, so we must then clear denominators on both sides. For each
, denote the greatest power of z that we divide by up to order
in this process by
. We work out an example where A is a smooth quintic 3-fold.
It suffices without loss of generality to assume that
is a single connected manifold A, as regards most aspects of the project. In case there is a subtlety, we address it as it arises.
A key result to keep in mind while reading the paper is the Proposition in Section 2.1, describing the T-equivariant normal bundles to the T-fixed sections of the exceptional divisor. The Proposition is used for both the Atiyah-Bott fixed-point localization theorem for
in Section 2.2, and for stating the twisting construction in genus-0 Gromov-Witten theory in Section 7.1 for
.
1.8. T-Fixed Strata of
Recall that L gives rise to
as the zero locus of a generic section. The tautological line bundle with fiber
, i.e. the
bundle, over the exceptional divisor
is central to the results.
The T-action on
induces a T-action on the moduli spaces of stable maps to
, which in turn induces a T-action on the universal cotangent line bundles at each of the marked points. For a given T-fixed stratum
of
and a line bundle
with a fiberwise T-action, we refer to the class
as the T-weight of
at
. The T-fixed strata of
are in comparison with those of E as follows. The stratum
of E is replaced by
, which is canonically diffeomorphic to
. Let
take on the values
as a substratum of
, as well as
.
Example 1.8. If
is a T-fixed stratum in the complement of the exceptional divisor, then take
in Example 1.4.2. If
is a T-fixed stratum in the exceptional divisor, then take
in Example 1.4.2. In either case, set
in Example 1.4.2 and also define
.
Finally, set
.
For each T-fixed section
of E, the strata
of E is canonically a stratum of
that we also denote by
. Lastly, there are T-fixed strata of
that have no counterpart in E. Namely, each T-equivariant line bundle summand of
gives rise to a T-fixed section over A in the exceptional divisor.
In the case
,
will denote (Section 2.1 for the definition)
rather than the pullback to
(which is modded out as in Section 2.1). Thus,
is given a new definition in this case. Let also
take the value
.
In particular (Section 2.1), the summand
gives rise to a section
over A in the total space of the exceptional divisor. The T-fixed set
is only a proper subset of the T-fixed stratum
. Thus we must check the conditions 1.a) and 2.aa) for the projections to
(see Section 7.3 for the integral asymptotics of
), and not for
, for the series
.
From now on let the symbol
stand for the T-fixed strata denoted
above, or for the “substrata”
of
. Let us denote the situation of a torus fixed point
connected to
by a 1-dimensional edge of the momentum polyhedron of a fiber of E, by
. In this case
,
, and
. Let
be the coordinate from
and
the coordinate from
. Similarly, we have the notation
and
. In the next section, we enhance this description of the T-fixed points of E to a description of the T-fixed points of
.
2. Geometry of
2.1. Geometric Preliminaries and Decomposition of Cohomology
The action of T on E decomposes
into a direct sum of 1-dimensional eigenspaces,
Let
be an ordering index of these eigenspaces, where the index value
corresponds to the bundle
, and
indexes the summand of
with T-weight
. Denote the T-fixed section of
corresponding to the index
by
. In the
case, we need to include the index a, for the divisors of B along which we replace the geometry of E by the
geometry. The strata
is connected to the strata
by the T-invariant edges
. Denote by
the T-weight of
.
Denote by
the composition of
with the projection to the base B. It is now mandatory that we introduce the diagram

Let
be the normal bundle within
to the T-fixed section over A with index
in
.
Proposition. The action of T on
decomposes
into a direct sum of T-equivariant line bundles, whose T-equivariant Euler classes are the elements of the set
Let us now turn attention to the restriction map
. Denote
the T-equivariant Euler class of the
bundle on the exceptional divisor. By the Lerray-Serre theorem,
In the following, we extend the definition of
to the entire
. With this interpretation of
, recall the isomorphism of vector spaces [15]
where the quotient is an additive quotient and
. On the other hand,
. The restriction of
to the exceptional divisor is
, which restricts to
to
.
Let us assume that
, so that
This holds true in the examples of quintic 3-folds for which the base is projective space. More generally, examples follow from the Lefschetz hyperplane Theorem and the Hard Lefschetz Theorem.
The restriction map
and the Poincaré pairing give the orthogonal projection
:

The short exact sequence
gives a direct sum decomposition
with respect to the Poincaré-pairing on
.
The result of “division by
” is only defined at the level of coset representatives of
. The choice of a basis of coset representatives from
suffices for integration over
weighted by
, which represents integration over the fundamental class of
. Thus, the subspace
represents the span of an arbitrary basis of coset representatives from
, and is not uniquely defined. The space
can be thought of as
.
For the purpose of integrating over fundamental cycles, the pullback
,
, of b to
can be described with respect to
by a multiplicative factor of
,
Let us now establish that
Both are subsets of
. In general, the subspaces can differ only on
, about which the Hodge diamond is symmetric w.r.t. the Lefschetz theorems. The inclusion is clearly an isomorphism when the base is projective space.
Thus,
,
Thus,
. This gives the inclusion. Finally, taking the quotients of
gives
Let us assume the map on the LHS is an isomorphism (an equality). This is also assumed as hypotheses for the main theorem (Section 4) and Theorem 2.
The RHS is used in the comparison of projection maps. Then,
and
extend to
by
and
respectively.
2.2. Fixed-Point Localization
For each
, the action of T on
decomposes
into a direct sum of 1-dimensional eigenspaces. Define
as in Example 1.8. Let
be the classes that restrict to the T-equivariant Poincaré duals of the torus-invariant divisors in the fibers of the exceptional divisor
:
The Atiyah-Bott Theorem says that the pairing of a class
against the fundamental class of
is given by
Namely, we sum over each of the T-fixed strata
the pairing of the class
against the fundamental class of
.
Thus, denote
the class in
that restricts to the T-equivariant Euler class of the
bundle on the exceptional divisor, and restricts to zero at all T-fixed strata in the complement of the exceptional divisor.
Define a T-equivariant line bundle
over the union of torus-invariant edges of
as follows. It restricts to the
bundle over the edges of the exceptional divisor, restricts to the trivial bundle over the edges
and whose T-equivariant Euler class restricts to
over the edges
.
Proposition. The
pairings on elements of
take values in
.
Proof. The restriction of
to the union of torus invariant edges coincides with the class
. Apply the Atiyah-Bott fixed-point localization Theorem to the restriction of
to the union of torus-invariant edges of
,
and
for all
. Thus,
induces an element of
.
3. The htA Function
Let
be the coordinate along
. Let
be a basis of
, and
a basis of
, with dual bases
and
. Let
be coordinates on
. Define
Quantum Lefschetz Theorem [1] [16] [17]. Suppose
, or more generally that L is convex. Then for each
and for each smooth family
, the series modification
lies in the image by
of the Lagrangian cone associated to the genus-0 Gromov-Witten theory of A with domain inputs
encoded by coefficients of
by the dilaton shift.
Let us assume that
has the property (Div + Str primary) that its dependence on
is of the form
where
do not depend on
, are Laurent polynomials in z valued in
, and
. Then, both series
and
have the property Div+Str primary.
In the case that
define
by
. Let us define a partial order on
by
if
. In the case that the inclusion
is only proper, our goal is to prove well-definedness of the least positive integer function
such that, for each
, the truncation of
to order
on both of
and
in the Novikov’s variables of the base is a formal linear combination of vectors in the linear space
(both sides truncated to order ≤ D on both of
and
),
where
.
The need for this is as follows. Condition 1.a of Theorem 2 refers to twisted Lagrangian cones of the Gromov-Witten theory of A. The Quantum Lefschetz Theorem also refers to the (image by
of the) Lagrangian cone of A, but does so in terms of a family of points of the (image by
of the) Lagrangian cone of the Gromov-Witten theory of B. The difficulty is that the Quantum Lefschetz Theorem only uses certain terms of the series-those that lie in the Novikov ring associated with
. The input for the Main Theorem is a family of points on the Lagrangian cone of B, which uses the Novikov ring of B.
The difficulty with this is that the Mori cone (resp Novikov ring) of A is only a subcone (resp. subring) of the Mori cone (resp. Novikov ring) of B. The natural algebraic tool for working with Langragian cones in genus-0 Gromov-Witten theory is the Birkhoff factorization technique. We will do this using the divisor equations. Thus, assume
is generated by
, in which case
is generated multiplicatively by
.
We now prove well-definedness of
by giving a combinatorial algorithm for computing it. We observe the following (Divisor-, String-) differential equations
For any polynomial
in variables
with coefficients in
, it follows that
Define
recursively:
Now replace the series
by a differential operator series. Let
be the (maximal) pole order of
at
. Then define
through the formula
Namely, expand the RHS (right-hand side) at order D,
to get the formula for
in terms of
, inductively. Define
and
Let
be the unique5 family of points of
whose truncation to order
on both of
and
in the Novikov’s variables of the base satisfies
.
Example. Let
, and
a smooth quintic 3-fold.
Let
be the Kähler generator of
, and take
to be the J-function of
at the point
,
Thus, we deduce the relation
. The A series has been reindexed relative to the original A series.
The coefficient of
in
is
This is a polynomial in powers of the nilpotent of maximal non-vanishing degree 3 variable
, with coefficients in
.
Then,
determines
recursively:
A quick check by induction shows that
when n is a positive multiple of 5, in which case
. Also by induction, for each
for which n is not a multiple of 5,
is the maximal power of
in the
series; i.e.,
. The preceding discussion allows us to deduce the following.
Proposition. Suppose that
is not surjective, so that
is not identically zero. If B is
, if A is the zero locus of a generic section of a convex line bundle L over B, if
is the J-function of B, and if the class
of the base is nonnegative as a functional on
, then
.
Proof. Group each numerator factor with a denominator factor and expand analogously to the above. Each factor in the denominator that is not grouped with a factor in the numerator gives a power of
beyond those that come with powers of
.
4. Main Results
4.1. The I-Function
Upon extension of scalars
of homology groups, the Mori cone of
includes into
. Given
or
, define
,
,
,
, and these values uniquely determine
.
Henceforth we use the gamma function convention:
Let us assume the conditions in Section 3 hold true. Our main theorem assumes the hypotheses of Section 2.1; however, the latter hypotheses may not be necessary (as noted in Section 5.3). Then,
Main Theorem. Let E be a toric fibration over base B, whose fibers are not copies of the point, and let
be a T-fixed section. Let
be convex line bundles over B, and
smooth divisors of B arising as the zero loci of generic sections of
. Further assume the
to be mutually disjoint. In the Case 1 below, assume
is generated by
, so that each
is generated multiplicatively by
.
Case 1: If the push-forwards
do not identify the Mori cone of
with that of B, then for each
, for each
, for each
and for each smooth family
with the property Div + Str primary, the
version of the series
(a completion6 of)
defined by
lies in the truncation to order
on both of
and
(in the Novikov’s variables of the base) of the Lagrangian cone associated to the genus-0 Gromov-Witten theory of
. Case 2: If the push-forwards
identify the Mori cone of
with that of B, then
, and the preceding series lies in the preceding cone without any truncation condition on either, while still assuming the property Div + Str primary for the smooth family
.
Since the genus-0 generating functions of Gromov-Witten theory of E and
are described in [8] , we may think of the main result as a gluing result or a gluing formula. Similarly, the
integral (Section 7.3) is defined in terms of the integrals for
and
.
Remark. When the fibers are copies of the point then we omit the sum over
and we set
to zero, since the projective fibers are also copies of the point. Keeping these interpretations in mind, the theorem remains true when the fiber of the toric fibration is the point. The theorem reduces to the statement
.
Remark. The natural generalization of the Main Theorem to the case of several T-fixed sections of E coincides, at the first level of analysis, with the natural generalization of the mirror theory of Section 7.
Remark. The analogue of the proof of Theorem 2 in [8] indicates the dependence of points of
upon domain variables from
.
Conjecture. The dependence on domain variables
may be incorporated into the Main Theorem by replacing
in the argument of
and
in the argument of
, for some function
,
. The latter shift of the argument of
by u is free, and then the shift of
is determined.
Some examples of the main Theorem.
1) Let B be a smooth toric variety obtained by
-symplectic reduction of
and A a (nef) coordinate hyperplane divisor of B. An instance of
in this case is the example in Section 1.6. The series
, constructed from
, is not supported in the Mori cone of
. See the inequality conditions on the support of the series, in the Remark in (2.bb) of Section 6. However, if we construct the series
from
then the latter conditions at the fixed point
are updated by the additional condition
. The class
is, apriori, an element of
. If the bundle L is considered as
-equivariant, then
is
-equivariant. The class
is not the same equivariantly as
, but they define the same functionals on the Mori cone of
. The above inequality reads
. This inequality rules out
“the class of a
in a fiber of the exceptional divisor”, as well as the curve classes
, from the solutions to the original set of inequalities in the Remark.
Thus, the series of the Main Theorem is an extension outside the Novikov ring of the series of the toric mirror theorems, in example 1.5 and more generally for symplectic toric manifolds [6] [7] [8].
2) Let B be
,
and A the manifold of complete flags in
.
Corollary. Let E be a toric fibration over base B, whose fibers are not copies of the point, and let
be a T-fixed section. Then for each
, for each
and for each smooth family
with the property Div + Str primary, the
version of the series
lies in the Lagrangian cone associated to the genus-0 Gromov-Witten theory of
.
Application to codimension > 1 subvarieties
. Let
be a symplectic reduction of a direct sum of line bundles pulled back from A, and
a symplectic reduction of a direct sum of line bundles also pulled back from A. T-fixed sections
and
may be considered as index subsets, respectively. The disjoint union of index subsets defines a T-fixed section
. Then Corollary applies to
, where the matrix used for the symplectic reduction is block diagonal with a block for each of the fibers.
4.2. Graded Homogeneity
Let
be a basis of
extending a basis of
. Define
for all Novikov’s variables
. This determines the degrees of Novikov’s variables
as follows:
, let
denote the coefficent of a along the basis vector
. Thus,
and
. Let us refer to Sections 1.8, 2.1 and 2.2 for the definition of classes
and for the projection maps
and
onto subspaces of
. The first Chern class of
away from the exceptional divisor is the restriction of the first Chern class of TE. The first Chern class of TE is
.
Let
be any T-fixed stratum in the complement of the exceptional divisor. The tangent space to the fibers of E at
decomposes as the direct sum of the line bundles with the equivariant first Chern classes
. Since the classes
all vanish, the above formula for the first Chern class accounts correctly for the normal bundle to
in E (Section 1.2). On the exceptional divisor, the tangent bundle of
restricts to
. The
fiber line summand, along with the
and
maps, will give the difference between the tangent bundle to the projective bundle itself, and the pullback of
from the ambient space.
At each T-fixed section
on the projective space bundle over A, refer to Section 2.1 for the first Chern classes of the normal line bundle summands. Then, the first Chern class of the preceding is
, as follows. The dimension of the fiber of E is
, and there are
T-fixed point sections of the projective bundle fibers of the exceptional fibers. At each
, the first Chern class of one of the
line bundle summands,
, vanishes. Thus, we get
contributions to the first Chern class of the tangent bundle to the projective space fibers at each such T-fixed section. Thus, we arrive at
for measuring the degree of
,
. The restriction of the class
to fibers of
is the dual vector to the
fiber curve classes.
The class
vanishes away from the exceptional divisor. Now compare the preceding formulae for
to the universal formula
The latter restricts correctly to the exceptional divisor and to the standard locus.
Let us now check the degree of the total series
is
. The degree of
is 1. Then, for each
, the term
is of degree
. Thus, if we simply define
, then the degree of the latter becomes 1. When the factor
is included we thus arrive at degree
, which is independent of
. Let us note geometry of the latter definition of
, as follows. The summand
from
contributes to the pairings
. The data beyond
to determine a class
is the pairing
, realized as
This is the latter degree of
, for all
.
Then compare the degrees of the terms
, where
is defined by
and
, with the degrees of the hypergeometric factors. Then, the remaining terms of the main series are of total degree 0, as follows. If
and
, all factors are denominator series with the total degree
In the case
, the “denominator” series with upper limit
is actually a numerator series. The index goes from 0 to
, giving
factors in the numerator rather than the denominator; thus the preceding counting of
is correct in this case too. Let us simply note that the degree counting is the same in all cases. Thus, the mechanism that establishes the degree formula is the ratio of infinite products, from Section 4.
The degree of
Novikov variables is
. Thus, this need only be compared to the hypergeometric factors of the series. In view of the above remarks, we compare the Novikov variables degrees to the upper limit indices on the product series. The Novikov variable degrees and the product series degrees should be equal, so that they cancel out to 0. The comparison is immediately verified.
5. The T-Equivariant Cone
5.1. Localization of Stable Maps
The work of Graber-Pandharipande [18] justifies the fixed-point localization technique for computing integrals of T-equivariant cohomology classes over virtual fundamental cycles in the moduli spaces of stable maps to
. Here the T-equivariant normal “bundle” to a T-fixed stable map is actually a virtual (orbi-) virtual bundle in T-equivariant K-theory. The description of T-fixed stable maps is then analogous to the description in [8]. Namely, the connected components of the T-fixed loci in the moduli spaces of genus-0 stable maps are fiber products of moduli spaces of genus-0 stable maps into the T-fixed strata of
. Let C be a leg of
; i.e., an irreducible component of
that maps surjectively to a T-invariant edge of (a fiber of
of)
. The fiber product is defined by reference to the curves from
, from
and toric edges
. The image points
and
coincide with the images of marked points of stable maps from
and from
in their roles as nodal points of
. There is also the case that either
or
may be a marked or unmarked point of
, not connecting C to any other curve component of
.
There are three disjoint cases to consider, depending upon how the 1-dimensional
-orbit
(i.e., edge) intersects the exceptional divisor. Equivalently, these cases are distinguished by the projection
image of the point set
. Firstly (2.bb), the projection of the toric edge along the projection
map is again a toric edge at each point of the given fiber product. Suppose that the two strata connecting a toric edge map via the projection
to the T-fixed sections
and
. The fibre products involving factors of genus-0 stable maps into
can be non-compact, as follows. Given a toric edge connecting
to
, the nodal point in
is unable to enter the exceptional divisor. The Atiyah-Bott formula7 implies that the correct cohomology group to use for the non-compact space
is the subset
. A similar case to consider is when the toric edge connects to
, where
.
Secondly (2.ab), the T-fixed points of the toric edge connect to the rest of the T-fixed stable map at
and at
;
. In this case too, the projection
image of the toric edge is also a toric edge.
Third (2.aa), the toric edge is contracted by the projection
map at each point of the given fiber product. The T-fixed points of the toric edge connect to the rest of the T-fixed stable map at
and at
,
.
There are three types of terms that contribute to the series
. Namely, the polynomial term
, and then two types of contributions to the
projection of the series
. Given a T-fixed stable map to
, which we denote by
, now let C be the smooth irreducible component of
that contains the first marked point of the source of the stable map. In order for the stable map
to contribute to
, f must map the first marked point into the stratum
. The latter two types of contributions are determined by whether
i) All points of C are mapped by f into the T-fixed stratum
. In this case, let
be the maximal connected subset of
containing C that maps to
, and let
.
ii) C maps to a T-invariant
in
connecting T-fixed strata
and
. Let us assume that, in the normalization of
, C is a
with two marked points—which we may take to be 0 and
via the action of
on
—, that there is a marked point of
at
, and that the marked point at
corresponds to a node of
. Thus the stable map takes C to a
, maps the first marked point of
at
to
and maps
to a nodal point of the stable map at
, and as it follows from the work of Kontsevich [19] , is given by
.
Each point of
lies in either the (normal bundle to the) exceptional divisor, or its complement—this is close enough to the toric bundles case for the following decomposition in [8] to hold, since the details are local.
Let us recall (Section 1.8) the definition of
. The fiber of the virtual normal bundle to the T-fixed strata of stable maps to the T-fixed strata
at the T-fixed stable map
, as in case i) above, is given by
The virtual normal bundle
to the T-fixed stable map with source
, deforming the map to a non T-fixed stable map, decomposes into the direct sum of:
i) The virtual normal bundle over the stable map with source
, and
ii) A virtual vector space
over the point
. This virtual vector space is the fiber of a virtual bundle. Let us use the same notation for the bundle and for the fiber.
This is along the same lines as in [8] , with the only new subtlety coming from the case when
. Namely, the deformation of a stable map to
along a section of the bundle
is a stable map into
and is still T-fixed. If there are no componenents of
of type ii) connecting to the domain curves of the latter maps of type i) then, the line bundle
does not contribute to the virtual normal bundle to the fiber product factors of stable maps to
(or
) in the T-fixed loci in the moduli spaces of stable maps to
. For more details of this subtlety, see the decomposition of the map
near the end of 5.2 (with slightly expanded definition of C.).
A second technical issue regarding the T-equivariant deformation theory of f, comes from the case that the
bundle contributes to the T-equivariant normal deformation theory of
, but not to the restriction of f to the component
(of
) of
that connects to C in
. This mismatch can occur at
(or
), but does not occur in the toric bundles case. This case requires modifying the
-term of the deformation bundle from i) to
, where
maps all points of
to the image of the nodal point
.
This bundle is not quite what is needed for geometrical deformation theory. For that, we might take the bundle of sections of
that restrict to
over A. However, that will not suffice for reasons that follow. In any case, we need some bundle that contains
to use in the role of the third non-zero term in the short exact sequences defining the gluing maps of the deformation theory.
There is the complication here that we don’t want the
bundle to contribute, via the Quantum Riemann Roch theorem, to the twisted cone
. Thus, the present solution to the deformation problem would not be consistent with the twisted cones conditions.
Let
be an index value for local cooordinates with non-trivial T-action, as in Section 6. Let X be either the fiber of the toric bundle E or of the total space of the normal line bundle to the projective space bundle
of the exceptional divisor.
In Appendix 1 of [8] , we described T-equivariant line bundles
defined as the normal line bundles to the
local coordinate hyperplane divisors on the fibers of X;
. For
= “else” (Section 6), the associated T-equivariant line bundle is
; the corresponding divisor is
, by definition. Let us recall that T acts trivially on the pullback
The normal line bundle
along the exceptional divisor extends to the T-invariant edges of
as
(see Section 2.2). The line bundle
is in the role of
, for the index value
= “else”.
Let
be an equivalent notation for
, etc. There is an ambient set on which the ingredients
are defined by subsets, as the direct sum over
in such subsets. In the case of toric bundles, the ambient set is
. In the present geometry, in the case that
, the ambient set is
.
Define
(resp.,
) to be the direct sum over T-equivariant line bundles with non-trivial torus action
for which
is negative (resp., non-negative). Similarly, define
(resp.,
) by replacing C by
in the above definitions.
Let us consider the identity
In the toric bundles case, the equation holds only in (T-equivariant) K-theory. Namely, the LHS is missing the direct summands
for all values of
(which are T-equivariantly trivial), when
.
The first set in parentheses on the RHS is interpreted as “an element of the ambient set is considered as
; i.e., as an element of one of
,
”. The remaining three direct summands (counting
as well) are interpreted similarly by a Ven diagram.
The LHS in the present case, in analogy with the Appendix in [8] , is dependent upon
, so we need to update the LHS by
, which we define as follows.
Let us now refer to Appendix A. 7-9 to elaborate.
In the first case, the summand with index
contributes to the T-equivariant
deformation theory, since the pairing of the
bundle on C is
.
Let
be the connected component of
, connecting to C, that maps to
(or
). The direct summand L of the coefficient sheaf of
is for the gluing construction defined by short exact sequences that glue the separate deformation bundles from the fiber product of stable map moduli spaces. Namely, the direct summand L provides constant deformations (within the T-fixed stratum
) of
i), to coincide with the given deformation of
at
ii). The direct summand
from ii) is deduced as a result in [8] ; it is not a definition. By analogy with the derivation there, in the case that
, define
In the case that
,
In the case that
,
which can be understood (from eigenspaces, though not established further here), in terms of
. In the formula for the recursion coefficient in terms of
and the deformation bundles, the
term contributes the factor of
.
Define
In the case
,
; else
. See Section 5.3.
The formula for
is given in terms of
,
,
,
, and thus can be expressed independently of
, as in Corollary A.4 in [8] ; i.e.,
In particular,
depends only on
, and not on
.
The numerator factor
does not contain the
terms in the product formula, while the denominator
includes the
terms. The numerator
term then contributes the
terms to the
class, and cancels the
terms from the
class. This gives the product formulae in Section 5.4, defined by the analytic continuation in Section 4.1.
The factor of
must also be verified by the fixed-point localization formula for gluing nodal curves, in the moduli spaces of stable maps. This gluing was worked out for the toric bundles case in Appendix 3 in [8]. The factor of
, from one of the numerator8
factors, in the formulae for
(Section 5.4) from fixed-point localization, is used as the Poincaré-dual of A as a submanifold of B, as follows. Consider the
terms in the formula for
. The leg with the first marked point is mapped to the toric edge in the recursion relation, and the cohomology class representing the toric edge is restricted to A by Poincaré-duality by the factor of
as follows
,
The description here counts deformations along
on C at
, and along
on
at
respectively, glueing them at
for a global deformation, when they can be identified for glueing. The overcounting is then removed by subtracting
at
, by including it in the overall subtraction of
in the formula for
. This is along the same lines as for toric bundles themselves.
An equivalent description for the deformation theory, would be to keep the deformation on C, remove it on
and remove it on
. Keeping it on C has the affect in geometry of restricting
to
. This description gives the correct twisted cones condition for
. Thus, we update the preceding deformation theory description accordingly, which only modifies
and omits the summand
.
5.2. A Key Ingredient of Theorem 2
Let
have the same meaning as in Section 5.1 case i), and reserve the notation C for case ii) except that the first marked point will also be allowed the role of nodal point of
attaching C to
. As in 5.1 the connected component of
in the space of T-fixed stable maps into
is a fiber product of stable maps into the T-fixed strata of
. A tree with root C may be attached, via a nodal point, to stable maps
carrying the first marked point of
. The smoothing of such a node deforms
away from the locus of T-fixed stable maps into
. The inverse T-equivariant Euler class of the latter smoothing mode is given by
where
is the smooth point of
in the normalization of
that corresponds to the latter nodal point of
. Its presence is required by the fixed-point localization technique. The tree with root C yields a cohomology class of B that is proportional to
in contribution to the terms of type ii) in
. Let us observe that if we substitute
, then we get the inverse T-equivariant Euler class
of the latter smoothing mode. Let us integrate last over the moduli of
where
is defined as in i). The precedingly described nodal attachments to
, with
effectively yield new descendant input terms to the integrals over moduli of type i) in
.
If the tree with root C is rooted at
there are two possible ways
can intersect with the stratum
at
, according to the decomposition
. Namely, the image by
constrains
to lie in
, while
may be interpreted as constraining
to lie in
.
Define
“the sum of all contributions to ii) where the first marked point of
is contained in C ”.
Let
be the completion of
(Example 1.8) by allowing additional additive terms that are infinite z series at each order in Novikov’s variables, of the form
where
and
. Denote by
restrictions
of
where
is expanded in non-negative powers of z.
When the image of the first marked point
lies in
(resp.,
), the series
is constructed as a power series in z, from the cohomology
(resp.,
) with coefficients in
. The source component C from ii) maps to different cases of T-invariant edge curves, depending on the image of the marked point
. The trees
can be described by the data of Theorem 2, in Section 5.4. The series of our main theorem, which is verified by the techniques of Section 5.4, thus gives a special case of the trees
(by Section 5.4). Intuitively, the trees
should be described by formulas with some degree of similarity, by reference to the main series.
In the following let us simply note how the numerator twisting factors in the Quantum Lefschetz theorem cancel with some of the factors from the denominator series. This is interpreted in terms of twisted lagrangian cones (an ingredient in Section 5.4) by the Lemmas in Section 7.3.
Begin by writing the main Theorem in terms of
, rather than in terms of
, using the quantum Lefschetz Theorem. The twisting factors cancel with a denominator series. The particular denominator series depends upon the direct summand
for the restriction of the series
. In the first case, the denominator series
is partially cancelled by the preceding numerator series. In the second case, the denominator series
is partially cancelled by the preceding numerator series. The
is from the shift of the summation index for
, in Section 6.
The preceding observations establish that
is the point of the
-twisted Lagrangian cone of
with input
. Let us denote this Lagrangian cone contained in
by
.
5.3. Recursion
Finally, apply the discussion in 2.2 and 5.1 combined with the general computational details given in [8] to compute9
Given two of the T-fixed strata
and
connected by an edge, define submanifolds of each where the strata intersect with edges connecting the two strata. The two submanifolds are diffeomorphic, call it
, by the connecting edges.
The discussion in 5.1 and in 5.2 gives the recursion relation along the same line of argument as in Appendix 2 of [8] :
where
and
Let us note the orthogonal10 direct sum decomposition
. Both direct summands are
--modules. The role of
,
is understood by observing that
are valued in
. Recall from Section 2.1 (up to isomorphisms) the inclusion
. This gives a way to interpret the
-module structure. The map
in the recursion relation
is applied to a multiple of
from the recursion coefficient
.
Perhaps the
operators in the recursion relation
can be composed with suitable projection maps, defined w.r.t. the Lefschetz decomposition so that both sides of the recursion refer to the same ambient vector space, while still sufficing for Theorem 2 (Section 5.4). The author has not worked in this generality.
5.4. Theorem 2
Theorem 2. Points
of the overruled Lagrangian cone of the T-equivariant genus-0 Gromov-Witten theory of
are characterized by the conditions:
(1.a):
(1.b):
(2.bb):
(2.ab):
(2.aa):
:
In the case
, we are nearly in the case (2.aa) as far as considering the LHS of the recursion relation as nearly a point of
, as follows. The normal bundle to A in B doesn’t deform curves into A out of the T-fixed loci in the moduli spaces of stable maps to
. Recall that the line bundle
is the restriction of the tautological line bundle
to the T-fixed section
. The normal bundle to A in B thus extends over the T-fixed curves
. Then, local sections of the extended normal bundle do deform multiple covers of the latter curve out of the T-fixed stratum in the moduli spaces of stable maps to
. Hence, the inverse T-equivariant Euler class of the associated deformation bundle contributes to the fixed-point localization formula in the moduli spaces of stable maps.
Aside from the many cases to consider, the proof is identical to the proof of the corresponding Theorem 2 in [8].
6. Recursion
To prove the equivariant version of the Main Theorem, it suffices to show that
satisfies conditions (1.a), (1.b) and (2) of Theorem 2.
Define
The hypergeometric modifications
are
-series whose coefficients have simple poles at
when such values are non-zero, finite order poles at
, and essential singularities at
.
Thus, we need to show that: (1.a)
, (1.b)
, and (2) residues at the simple poles satisfy the recursion relations of Theorem 2. We check conditions (2) here by direct calculation of the residues. We check conditions (1.a), (1.b) in Section 7.
Our first goal is to argue that the series
is supported in the Mori cone of
,
. The mechanism that insures
this is to look at the support of the factors
of
for which
.
Proposition. Any element of
may be represented as the sum of a curve whose irreducible components are preserved by the action of T on
, and an integer multiple of “the class of a T-invariant
in a fiber of the exceptional divisor”.
Proof. Let
be a curve class in MC. The action of T on
is induced by that on E. We would like to take a lift of the projection
,
, which we may assume [8] to be preserved by the action of T on E; i.e., that
is represented by such a curve. Apriori, there may be any number of toric edge component curves among the curves representing
. These may intersect with a curve component of
in
. These toric edges each lift to the
in such a way that one of their T-fixed points intersects the exceptional divisor at a T-fixed point of a projective space fiber. The preceding irreducible component curves in
may be lifted to arbitrary T-fixed sections of the exceptional divisor. This may result in a disconnected lifted curve.
The curve classes are determined by their pairings with elements of
. Thus, add the multiple
of “the class of a T-invariant
in a fiber of the exceptional divisor” to the lift of
.
With the Proposition in place, let us now compare
and
. This will allow us to interpret the support conditions along
of the series
, in terms of
.
A first source of difference between the two comes from the inclusion
. Another difference is that the T-invariant
curves in
do not have any geometric analogues in
. However, the latter curve may be represented as the sum of the class of a
and the class of a
in a fiber of the exceptional divisor. Thus all elements of
have geometric analogues in
.
Remark. Any curve from a fiber of
has a geometric analogue in
. The
’s are determined by the geometry of E, and thus have the same meaning whether pulled back to
or to
. The class
is determined11 by the local geometry of the exceptional divisor and thus has the same meaning whether referred to
or to
.
(2.aa) Residue of
at
. Given
, rename
and
, and then redefine
and
,
Then, the pairings
translate into
.
The classes
, contribute in terms of
(resp.
) to d (resp.
) from the definition in Section 4. Such contributions from
are accounted for already, by redefining the summation indices d and
as above. Then, the remaining contributions to d (resp.
) are from the Mori cones of the fibers.
Proposition. The series
is supported in the Mori cone of
.
Proof. For
, the support of the series
is
characterised by the inequality
. For each
, the support of
the series
is characterised by the inequality
. Let us now
argue that the set of solutions
to the same inequalities is contained in
. By the comparison of
with
, and by the Remark, it suffices to establish the analogous result for
. This follows from the Corollary and the same (strictly speaking, analogous) inequalities that arise there, as a special case of a general result in toric geometry describing the Mori cone in terms of inequalities.
In the following recursion verification, let
.
For the
recursion relation, the
series takes values in the image of
. We noted the role of
in the recursion coefficient for this purpose, at the end of Section 5.3.
Residue of
at
. Given
, rename
and
, and then redefine
and
,
Then, the pairings
translate into
.
Proposition. The series
is supported in the Mori cone of
.
Proof. For
, the inequalities describing the support of the series are
and
, whose solution set is “a subset of
”
“the class of a
in a fiber of the exceptional divisor”.
(2.bb) Residue of
at
. Let
be the delta-function
. Given
, rename
and
, and then redefine
and
,
The pullbacks
vanish. In particular
, and
Then, the pairings
translate into
.
Proposition. If
then the series
is supported in the Mori cone of
.
Proof. The support of the series
is characterised by the
inequality
. The terms of the series that determine the remaining support conditions are those with
; i.e.,
. The set
coincides with the set
. For each
, the
support of the series
is characterised by the inequality
. For each
, the support of the series
is characterised by the inequality
. The proof proceeds as
in the case of 2.aa
.
Remark. For
, the inequalities describing the support of the series are
and
, whose solution set is “a
subset of
”
“the
class of a
in a fiber of the exceptional divisor” at each order
.
Since
for all
it follows that
. Hence the “index”
does not transform presently. Thus, the asymmetry between the factors indexed by
and
is removed for the purposes of the present recursion process. It follows that the present recursion process is identical to the toric bundles case [8] ,
as required.
In the case
then
is replaced by
. Then reverse the change in the summation index. This gives the recursion relation, as in all other cases. For
use “
” in the transformation of the
summation index, following the
case.
(2.ab) Residue of
at
. Given
, rename
and
, and then redefine
and
,
Then, the pairings
translate into
.