Twisted Bicategorical Shadows and Traces

Abstract

Bicategorical shadows provide a categorical framework that encompasses Hochschild homology and topological Hochschild homology (THH), encodes their Morita invariance, and extends the notion of trace from symmetric monoidal categories to bicategories. Certain equivariant variants, such as $C_n$-twisted THH, do not fit into the ordinary shadow framework. We introduce bicategories with $G$-twisting data and show that every ordinary shadow on such a bicategory induces, for each $g\in G$, a $g$-twisted shadow on the associated bicategory of $G$-twists. These $g$-twisted shadows are invariant under $G$-Morita equivalence; examples include $C_n$-twisted THH and twisted Hochschild homology of $C_n$-Green functors. We further define a $g$-twisted bicategorical trace that recovers the $g$-twisted Hattori--Stallings trace. For $C_n$-Green functors, the orbitwise $g$-twisted Hattori--Stallings traces assemble into a morphism of $C_n$-Mackey functors that, at the orbit $C_n/C_n$, recovers the degree-zero twisted Dennis trace.