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arxiv: 2606.29902 · v1 · pith:WM677FZFnew · submitted 2026-06-29 · 🧮 math.GT · math.AT· math.DG

An infinity-categorical TQFT from instantons

Fan Ye This is my paper

Pith reviewed 2026-06-30 03:58 UTC · model grok-4.3

classification 🧮 math.GT math.ATmath.DG
keywords instanton TQFTinfinity-categoriescobordism categories2-periodic chain complexesFloer homologymu-operatorslink spectral sequencecomplete Segal spaces
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The pith

The instanton TQFT extends to a functor CI from an infinity-cobordism category BI to an infinity-derived category D of 2-periodic chain complexes.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper upgrades the instanton TQFT, previously defined on ordinary categories, to a functor CI between two infinity-categories. The source category BI is obtained by modifying the standard infinity-cobordism category Bord_4 using complete Segal spaces so that it carries instanton data from families of metrics on cobordisms. The target category D is constructed via the dg-nerve of a dg-category whose objects are 2-periodic chain complexes over finitely generated projective Z-modules, with morphisms that are sums of homogeneous chain maps. This infinity-categorical lift simplifies the construction of the hypercube of chain complexes needed for the link spectral sequence and lifts the generalized cap product mu-operators to the chain level together with explicit homotopies and higher homotopies that witness commutativity in even degrees.

Core claim

The central construction is the functor CI from the infinity-cobordism category BI, built as a modification of Bord_4 via complete Segal spaces, to the infinity-derived category D obtained from the dg-nerve of 2-periodic chain complexes over projective Z-modules. The functor encodes the instanton TQFT at the infinity level, reinterpreting the data previously assembled by Kronheimer-Mrowka from families of metrics, and supplies chain-level lifts of the mu-operators with the required higher homotopies.

What carries the argument

The functor CI from the infinity-cobordism category BI (a Segal-space modification of Bord_4 carrying instanton data) to the infinity-derived category D (the dg-nerve of 2-periodic chain complexes over projective Z-modules).

If this is right

  • The hypercube of chain complexes for the link spectral sequence admits a simpler construction from the infinity-categorical data.
  • Generalized cap product mu-operators lift to explicit chain maps together with homotopies and higher homotopies witnessing commutativity in even degrees.
  • The information carried by families of metrics on cobordisms is reorganized as morphisms in an infinity-category.
  • The ordinary-category instanton TQFT is recovered by taking homotopy categories of BI and D.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same pattern of Segal-space modification and dg-nerve target could be applied to other gauge-theoretic invariants to obtain infinity-categorical versions.
  • The chain-level homotopies for mu-operators may allow direct comparison of instanton and other Floer theories at the level of A-infinity structures.
  • Higher morphisms in BI could encode additional geometric data such as families of metrics parametrized by higher simplices.

Load-bearing premise

The modification of Bord_4 into BI via complete Segal spaces produces a well-defined infinity-category that supports the instanton data, and the dg-nerve construction produces a target category D compatible with the required chain-level operations.

What would settle it

An explicit computation on a simple cobordism showing that the proposed functor CI fails to preserve composition of 1-morphisms or that the supplied higher homotopies for multiple mu-operators fail to satisfy the expected relations in the dg-category D.

Figures

Figures reproduced from arXiv: 2606.29902 by Fan Ye.

Figure 1
Figure 1. Figure 1: A systematic picture for n = 3 and some τ ∈ R 3 . We use small squares with Wi to denote the handles in Wi . Moving the small squares corresponds to modifying the metrics. • We need to apply Remark 7.12 to lift the result of a hypercube to a cube complex, in particular the sign changes mentioned in Remark 7.7. Then we consider the most general case. See [PITH_FULL_IMAGE:figures/full_fig_p071_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: A systematic picture for n = 3 and some τ ∈ R 3 × R 3 . We use small squares with Wi to denote the handles and use vertical lines to denote submanifolds. Moving the small squares corresponds to modifying the metrics and moving the vertical lines corresponds to modifying the sections. (1) We need to apply Remark 8.18 and consider larger but still disjoint regions {R′ i }i∈n containing suitable neighborhoods… view at source ↗
read the original abstract

In this paper, we upgrade the instanton TQFT from ordinary categories to a functor $CI$ from an $\infty$-cobordism category $\mathrm{BI}$ for instantons to an $\infty$-derived category $\mathsf{D}$ of $2$-periodic chain complexes and sums of homogeneous chain maps. The construction of $\mathrm{BI}$ is a modification of the $\infty$-cobordism category $\mathrm{Bord}_4$ constructed by Lurie and Calaque--Scheimbauer via complete Segal spaces. The construction of $\mathsf{D}$ follows from the dg-nerve of a dg-category of $2$-periodic chain complexes over finitely generated projective modules over $\mathbb{Z}$. The information encoded in the functor $CI$ was already developed by Kronheimer--Mrowka using families of metrics on cobordisms, but our reinterpretation through $\infty$-categories simplifies the construction of the hypercube of chain complexes for the link spectral sequence. In addition, we upgrade the generalized cap product $\mu$-operators in instanton Floer homology to the chain level and construct explicit homotopies and higher homotopies for commutativity of multiple $\mu$-operators in even degrees.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

3 major / 2 minor

Summary. The manuscript constructs an ∞-categorical instanton TQFT as a functor CI: BI → D. BI is obtained by modifying Lurie's Bord_4 ∞-cobordism category via complete Segal spaces to incorporate instanton data; D is the ∞-category arising from the dg-nerve of the dg-category of 2-periodic chain complexes over finitely generated projective Z-modules. The functor CI reinterprets Kronheimer-Mrowka's instanton Floer data, supplies explicit chain-level homotopies and higher homotopies for the generalized cap-product μ-operators, and simplifies the hypercube construction used in the link spectral sequence.

Significance. If the functoriality and homotopy constructions hold, the work supplies a higher-categorical language that makes the higher homotopies for μ-operators explicit and may streamline spectral-sequence arguments in instanton Floer theory. The approach reuses standard tools (complete Segal spaces, dg-nerve) rather than inventing new axioms, which is a methodological strength.

major comments (3)
  1. [§3] §3 (Construction of BI): the claim that the modification of Bord_4 via complete Segal spaces yields a well-defined ∞-category supporting instanton metric families requires an explicit check that the Segal maps preserve the families of metrics used by Kronheimer-Mrowka; without this, the source category may not carry the required data for the functor CI.
  2. [§4] §4 (Definition of D and CI): the assertion that CI is an ∞-functor is load-bearing for the central claim, yet the manuscript provides no verification that the simplicial maps induced by cobordism composition in BI are sent to chain-homotopy coherent maps in D; low-dimensional cases (objects, 1-morphisms, 2-simplices) should be checked explicitly.
  3. [§5] §5 (μ-operators and homotopies): the upgrade of the μ-operators to chain level with explicit higher homotopies is presented as a simplification, but compatibility with the 2-periodicity and the sum-of-homogeneous-maps structure in D is not shown to be free of sign or grading obstructions; this directly affects the claimed simplification of the link spectral sequence hypercube.
minor comments (2)
  1. [§2] Notation for the ∞-category D is introduced without a clear comparison table to the ordinary derived category used by Kronheimer-Mrowka.
  2. Several references to Lurie and Calaque-Scheimbauer are cited for the Segal-space construction but lack page or theorem numbers for the specific statements invoked.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the thorough review and constructive suggestions. The comments identify places where the manuscript would benefit from additional explicit verifications. We address each major comment below and indicate planned revisions.

read point-by-point responses

  1. Referee: [§3] §3 (Construction of BI): the claim that the modification of Bord_4 via complete Segal spaces yields a well-defined ∞-category supporting instanton metric families requires an explicit check that the Segal maps preserve the families of metrics used by Kronheimer-Mrowka; without this, the source category may not carry the required data for the functor CI.

    Authors: We agree that an explicit verification strengthens the argument. The construction of BI follows the standard complete Segal space axioms applied to the instanton data, but the manuscript does not spell out the preservation of metric families. In the revised version we will insert a dedicated paragraph in §3 verifying that the Segal maps send families of metrics on cobordisms to families of metrics on the composed cobordisms, using the same gluing and stretching arguments as Kronheimer-Mrowka. revision: yes

  2. Referee: [§4] §4 (Definition of D and CI): the assertion that CI is an ∞-functor is load-bearing for the central claim, yet the manuscript provides no verification that the simplicial maps induced by cobordism composition in BI are sent to chain-homotopy coherent maps in D; low-dimensional cases (objects, 1-morphisms, 2-simplices) should be checked explicitly.

    Authors: The definition of CI assigns to each simplex in BI the corresponding instanton chain map or homotopy, which is designed to be coherent by construction. Nevertheless, the referee is correct that low-dimensional coherence is not written out. We will add, in the revised §4, explicit checks for 0-, 1-, and 2-simplices: objects map to 2-periodic complexes, 1-morphisms to chain maps, and 2-simplices to chain homotopies satisfying the required coherence relations in the dg-nerve of D. revision: yes

  3. Referee: [§5] §5 (μ-operators and homotopies): the upgrade of the μ-operators to chain level with explicit higher homotopies is presented as a simplification, but compatibility with the 2-periodicity and the sum-of-homogeneous-maps structure in D is not shown to be free of sign or grading obstructions; this directly affects the claimed simplification of the link spectral sequence hypercube.

    Authors: The μ-operators are defined in even degrees and the target category D is built precisely to accommodate 2-periodic complexes together with sums of homogeneous maps; the even-degree condition eliminates the usual sign issues that appear in odd-degree settings. We therefore maintain that no grading obstructions arise. To make this transparent we will add a short subsection in the revision that records the degree parities and confirms that the higher homotopies remain within the allowed sum-of-homogeneous-maps structure, thereby justifying the simplification of the hypercube. revision: partial

Circularity Check

0 steps flagged

No significant circularity; construction assembles external tools

full rationale

The paper reinterprets Kronheimer-Mrowka instanton data as the ∞-functor CI: BI → D by modifying Bord_4 via complete Segal spaces (Lurie, Calaque-Scheimbauer) and applying the dg-nerve to 2-periodic chain complexes. All load-bearing steps invoke external, independently developed machinery whose compatibility is asserted by direct construction rather than by fitting parameters or reducing outputs to self-referential inputs. No self-citation chain, ansatz smuggling, or renaming of known results occurs; the central claim is a change of language that encodes the same information with explicit higher homotopies.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 1 invented entities

The central claim rests on the existence and well-definedness of the modified cobordism category BI and the compatibility of the dg-nerve target D with instanton data; these are domain assumptions drawn from prior ∞-category literature rather than new postulates.

axioms (2)
  • domain assumption The ∞-cobordism category BI can be obtained as a modification of Bord_4 constructed via complete Segal spaces.
    Abstract states this is the construction method used.
  • standard math The dg-nerve of the dg-category of 2-periodic chain complexes over finitely generated projective Z-modules yields the target ∞-derived category D.
    Abstract presents this as following from standard dg-category theory.
invented entities (1)
  • Functor CI no independent evidence
    purpose: Encodes the instanton TQFT as an ∞-categorical functor
    Newly constructed object in the paper; no independent evidence supplied in abstract.

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