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DefinitionDefinition: AI-adaptedProof: AI-generatedPipeline-generatedjudge pass (gpt-6-luna)
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Intrinsic localized pushforward for a proper fixed locus

Definition

Let T=(C×)r act on a smooth separated finite-type complex variety X with a finite invariant affine open cover. Let F=XT be proper, i:F↪X, pF:F→pt, and ST the character multiplicative set. Every notation ST−1HjBM,T(Y;Q) below means HjT(Y), the degree-j piece of the localization of the total graded module. By the finite-affine-atlas concentration isomorphism, i∗:ST−1HjBM,T(F;Q)→ST−1HjBM,T(X;Q) is invertible. Define the intrinsic localized pushforward

p∗loc:=pF∗∘(i∗)−1:ST−1HjBM,T(X;Q)⟶ST−1HjBM,T(pt;Q),

where pF∗ is the genuine proper Borel–Moore pushforward. For a homogeneous α∈HTq(X;Q) and smooth complex dimension d, an allowed insertion is α∩[X]T∈H2d−qBM,T(X;Q); the fundamental class [X]T is the complex-oriented class, not the cohomological unit 1∈HT0(X;Q). This construction does not define an ordinary pushforward along a nonproper map X→pt.

Definition references

[Equivariant pushforward by the fixed-locus inverse] Edidin–Graham, Section 4

[Borel–Moore proper pushforward and fundamental classes] Ginzburg, Section 1

Facts & Assumptions

Given: The torus action, the finite invariant affine cover, the proper fixed locus, and rational coefficients.

[A1]

AC is inherited through the normalized equivariant Borel–Moore construction and its concentration supplier. Localized torus-equivariant Borel–Moore classes BM concentration from a finite invariant affine atlas

[F1]

The normalized Borel–Moore groups, proper equivariant pushforwards, cap products, and fundamental classes use the preceding localized Borel–Moore definition. Localized torus-equivariant Borel–Moore classes

[F2]

Proper pushforward along the fixed inclusion is an isomorphism after character localization under the finite invariant affine-cover hypothesis. BM concentration from a finite invariant affine atlas

Proof

Given: The data in the Definition.

1.1A1F1F2given

By [F2], i∗ is an isomorphism in each degree after localization, and on the total graded localization its inverse is a unique degree-preserving ST−1RT-linear map; its restrictions give the degree-j inverses. The proper inclusion i and the proper map pF give the stated Borel–Moore pushforwards by [F1].

2.1F1F2step 1.1givenalgebra∎

Composition of the inverse with pF∗ is therefore a well-defined degree-preserving map on the localized Borel–Moore groups. The insertion convention is well-defined because [F1] supplies the cap action and the smooth complex orientation gives [X]T degree 2d. If X→pt is proper, functoriality gives pX∗=pF∗i∗, so p∗loc=pF∗i∗(i∗)−1=pX∗. If F=∅, then F→pt is proper and [F2] forces the localized groups of X to be zero, so the defined trace is the zero map. For r=0, T is trivial, F=X, i is the identity, and the properness hypothesis makes this the usual proper pushforward.

Depends on

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