Flow-category Hochschild homology conjecture

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Let Θ\Theta be a tangential structure, let RR be its associated ring spectrum, and suppose Flow⁡Θ≃Perf⁡(Rmod⁡R)\operatorname{Flow}^{\Theta} \simeq \operatorname{Perf}({}_R\operatorname{mod}_R). For F∈Flow⁡Θ\mathcal{F} \in \operatorname{Flow}^{\Theta} corresponding to an RR-bimodule MM, let RΔR_{\Delta} be the diagonal bimodule, and let Hom⁡R⊗Rop\operatorname{Hom}_{R \otimes R^{op}} denote homotopy classes of bimodule maps. Flow-category Hochschild homology conjecture. There are functorial isomorphisms

Ω∗Θ(F)≃π∗(M⊗R⊗RopRΔ),ΩΘ∗(F)≃Hom⁡R⊗Rop(M,RΔ),\Omega_*^{\Theta}(\mathcal{F}) \simeq \pi_*(M \otimes_{R\otimes R^{op}} R_{\Delta}), \qquad \Omega^*_{\Theta}(\mathcal{F}) \simeq \operatorname{Hom}_{R\otimes R^{op}}(M,R_{\Delta}),

and, under these isomorphisms, capsule concatenation corresponds to the displayed composition landing in

π∗(RΔ⊗R⊗RopRΔ)=:π∗THH(R).\pi_*(R_{\Delta} \otimes_{R\otimes R^{op}} R_{\Delta}) =: \pi_*THH(R).

The one-object computations verify the expected formulas in basic cases, while the functorial identification for general flow categories and its compatibility with concatenation remain conjectural.

References

Primary source

Noah Porcelli and Ivan Smith, “Spectral Floer theory and tangential structures”, arXiv:2411.03257 (2025).

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