Cotwist conjecture for functor categories on spheres

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Let D\mathcal{D} be a stable ∞\infty-category and let n\teq2n\teq 2. Consider the cotwist functor TFun⁡(Sn,D)T_{\operatorname{Fun}(S^n,\mathcal{D})} of the spherical adjunction

f∗:D↔Fun⁡(Sn,D):f∗.f^*:\mathcal{D}\leftrightarrow \operatorname{Fun}(S^n,\mathcal{D}):f_*.

For an E∞\mathbb{E}_\infty-ring spectrum RR, set D=RMod⁡R\mathcal{D}=\operatorname{RMod}_R, and let φ:R[tn−1]→R[tn−1]\varphi:R[t_{n-1}]\rightarrow R[t_{n-1}] be the equivalence determined by

φ(tn−1)=(−1)n−1tn−1.\varphi(t_{n-1})=(-1)^{n-1}t_{n-1}.

Cotwist conjecture. There is a commutative diagram in LinCat⁡R\operatorname{LinCat}_R identifying TFun⁡(Sn,RMod⁡R)T_{\operatorname{Fun}(S^n,\operatorname{RMod}_R)} under the equivalence Fun⁡(Sn,RMod⁡R)≃RMod⁡R[tn−1]\operatorname{Fun}(S^n,\operatorname{RMod}_R)\simeq\operatorname{RMod}_{R[t_{n-1}]} with φ∗[−n]\varphi^*[-n]. Moreover, if Stop⁡nS^n_{\operatorname{top}} is the topological nn-sphere and r:Stop⁡n→Stop⁡nr:S^n_{\operatorname{top}}\rightarrow S^n_{\operatorname{top}} is the antipodal map, then

TFun⁡(Sn,D)≃r∗[−n].T_{\operatorname{Fun}(S^n,\mathcal{D})}\simeq r^*[-n].

This predicts that the cotwist is controlled by the antipodal involution together with a shift by −n-n, and gives an algebraic description for module categories over an E∞\mathbb{E}_\infty-ring spectrum. The statement is presented as a conjecture because the preceding argument does not directly generalize to the spectral setting.

References

Primary source

Merlin Christ, “Ginzburg algebras of triangulated surfaces and perverse schobers”, arXiv:2101.01939 (2022).

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