Du Bois cohomology of noncommutative spaces and the Hodge numbers invariance conjecture for singular varieties
We extend the definition of cdh-sheafified Hochschild homology from varieties to stable categories linear over a field of characteristic zero, thereby proving its Morita-invariance. The dimensions of its homology groups give meaningful numerical invariants of a category; we combine them with invariants coming from topological K-theory and Poincaré duality to prove equality of mixed Hodge numbers for singular complex projective Fourier--Mukai partners in several classes in dimensions two, three, and four, including normal surfaces and threefolds with rational singularities and equal irregularity. Beyond these applications, we construct Du Bois versions of topological cyclic homology of stable categories together with appropriate multiplicative structures, prove a Geller--Weibel-type result for the variants of negative cyclic homology we introduce, and give categorical characterizations of cohomological purity of proper varieties and the $\mathbb{Q}$-factoriality defect of complex projective threefolds with rational singularities.