The adjoint-category functor conjecture

Let Vectinj{\mathsf{Vect}}_{\operatorname{inj}} be the category of finite-dimensional real vector spaces and injective linear maps, and let AdjCatn{\mathsf{AdjCat}}_n denote the (,1)(\infty,1)-category of (,n)(\infty,n)-categories with adjoints. For each inclusion RiRn\mathbb{R}^i\longrightarrow\mathbb{R}^n as the first ii coordinates, let ιi\iota_i forget all non-invertible morphisms of dimension greater than ii. The adjoint-category functor conjecture. There is a functor

AdjCat ⁣:VectinjopCat{\mathsf{AdjCat}}_{\bullet}\colon {\mathsf{Vect}}_{\operatorname{inj}}^{\operatorname{op}}\longrightarrow \operatorname{\mathscr{C}at}

sending Rn\mathbb{R}^n to AdjCatn{\mathsf{AdjCat}}_n and the inclusion RiRn\mathbb{R}^i\longrightarrow\mathbb{R}^n to ιi ⁣:AdjCatnAdjCati\iota_i\colon {\mathsf{AdjCat}}_n\longrightarrow {\mathsf{AdjCat}}_i. The conjecture is motivated by the expected graphical calculus for categories with adjoints, and is known in the restriction to dimensions at most two and (2,2)(2,2)-categories, but remains unproved in general.

Sources & referencesView supporting material

Primary source

Lukas Müller, “On the Higher Categorical Structure of Topological Defects in Quantum Field Theories”, arXiv:2505.04761 (2025).

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