Flow-category Hochschild homology conjecture

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

ΩΘ(F)π(MRRopRΔ),ΩΘ(F)HomRRop(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(RΔRRopRΔ)=:πTHH(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.

Sources & referencesView supporting material

Primary source

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

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