The noncommutative Hodge conjecture for small dg categories

Let A\mathcal{A} be a small dg category. Its Hodge classes are the subspace

Hodge(A):=π(j1(Chtop(K0top(A)Q)))HH0(A),\operatorname{Hodge}(\mathcal{A}):=\pi\left(j^{-1}\left(\operatorname{Ch}^{\operatorname{top}}\left(\operatorname{K}_{0}^{\operatorname{top}}(\mathcal{A})_{\mathbb{Q}}\right)\right)\right)\subset \operatorname{HH}_{0}(\mathcal{A}),

where Chtop\operatorname{Ch}^{\operatorname{top}} is the topological Chern character, jj is the map from negative cyclic homology to periodic cyclic homology, and π\pi is the projection to Hochschild homology. Noncommutative Hodge conjecture. The Chern character

Ch:K0(A)HH0(A)\operatorname{Ch}:\operatorname{K}_{0}(\mathcal{A})\longrightarrow \operatorname{HH}_{0}(\mathcal{A})

maps K0(A)Q\operatorname{K}_{0}(\mathcal{A})_{\mathbb{Q}} surjectively onto Hodge(A)\operatorname{Hodge}(\mathcal{A}). This is intended as a noncommutative, non-weighted version of the rational Hodge conjecture; it recovers the classical conjecture for the dg category of perfect complexes on a smooth projective variety and agrees with the formulation for admissible subcategories described by Perry.

Sources & referencesView supporting material

Primary source

Xun Lin, “Noncommutative Hodge conjecture”, arXiv:2102.03481 (2021).

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