The nullhomotopy-dependence conjecture for Floer-theoretic nearby Lagrangian torsion

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Let L⊂T∗S4kL\subset T^*S^{4k} be a Lagrangian homotopy sphere, and fix two nullhomotopies γt0\gamma_t^0 and γt1\gamma_t^1 of its stable Gauss map L→U/OL\to U/O. Let τ2k(L,γti)∈H4k(S4k;Z)\tau_{2k}(L,\gamma_t^i)\in H^{4k}(S^{4k};\mathbf{Z}) be the corresponding cohomology classes. Define E→S4kE\to S^{4k} as the stable real vector bundle classified by the composite map S4k→BOS^{4k}\to BO formed from a homotopy inverse to the projection L→S4kL\to S^{4k}, the map L→Ω(U/O)L\to\Omega(U/O) obtained by concatenating γ1−t0\gamma_{1-t}^0 with γt1\gamma_t^1, the Bott periodicity map Ω(U/O)≃Z×BO\Omega(U/O)\simeq\mathbf{Z}\times BO, and the map Z×BO→BO\mathbf{Z}\times BO\to BO.

Nullhomotopy-dependence conjecture. The classes τ2k(L,γti)\tau_{2k}(L,\gamma_t^i), for i=1,2i=1,2, differ by pk(E)p_k(E).

If true, this would make the Floer-theoretic nearby Lagrangian torsion well-defined as a coset modulo the image of pkp_k, yielding an invariant in R/λkZ\mathbf{R}/\lambda_k\mathbf{Z}. The source presents this as a conjecture and gives no evidence of a resolution.

References

Primary source

Daniel Alvarez Gavela, Kiyoshi Igusa and Michael Sullivan, “Legendrian and Lagrangian higher torsion”, arXiv:2603.28007 (2026).

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