No Arabic abstract
Let $k$ be a field. We show that locally presentable, $k$-linear categories $mathcal{C}$ dualizable in the sense that the identity functor can be recovered as $coprod_i x_iotimes f_i$ for objects $x_iin mathcal{C}$ and left adjoints $f_i$ from $mathcal{C}$ to $mathrm{Vect}_k$ are products of copies of $mathrm{Vect}_k$. This partially confirms a conjecture by Brandenburg, the author and T. Johnson-Freyd. Motivated by this, we also characterize the Grothendieck categories containing an object $x$ with the property that every object is a copower of $x$: they are precisely the categories of non-singular injective right modules over simple, regular, right self-injective rings of type I or III.
Categories over a field $k$ can be graded by different groups in a connected way; we consider morphisms between these gradings in order to define the fundamental grading group. We prove that this group is isomorphic to the fundamental group `a la Grothendieck as considered in previous papers. In case the $k$-category is Schurian generated we prove that a universal grading exists. Examples of non Schurian generated categories with universal grading, versal grading or none of them are considered.
We define a tensor product of linear sites, and a resulting tensor product of Grothendieck categories based upon their representations as categories of linear sheaves. We show that our tensor product is a special case of the tensor product of locally presentable linear categories, and that the tensor product of locally coherent Grothendieck categories is locally coherent if and only if the Deligne tensor product of their abelian categories of finitely presented objects exists. We describe the tensor product of non-commutative projective schemes in terms of Z-algebras, and show that for projective schemes our tensor product corresponds to the usual product scheme.
We investigate the notion of involutive weak globular $omega$-categories via Jacque Penons approach. In particular, we give the constructions of a free self-dual globular $omega$-magma, of a free strict involutive globular $omega$-category, over an $omega$-globular set, and a contraction between them. The monadic definition of involutive weak globular $omega$-categories is given as usual via algebras for the monad induced by a certain adjunction. In our case, the adjunction is obtained from the free functor that associates to every $omega$-globular set the above contraction. Some examples of involutive weak globular $omega$-categories are also provided.
In this paper, we study tensor (or monoidal) categories of finite rank over an algebraically closed field $mathbb F$. Given a tensor category $mathcal{C}$, we have two structure invariants of $mathcal{C}$: the Green ring (or the representation ring) $r(mathcal{C})$ and the Auslander algebra $A(mathcal{C})$ of $mathcal{C}$. We show that a Krull-Schmit abelian tensor category $mathcal{C}$ of finite rank is uniquely determined (up to tensor equivalences) by its two structure invariants and the associated associator system of $mathcal{C}$. In fact, we can reconstruct the tensor category $mathcal{C}$ from its two invarinats and the associator system. More general, given a quadruple $(R, A, phi, a)$ satisfying certain conditions, where $R$ is a $mathbb{Z}_+$-ring of rank $n$, $A$ is a finite dimensional $mathbb F$-algebra with a complete set of $n$ primitive orthogonal idempotents, $phi$ is an algebra map from $Aotimes_{mathbb F}A$ to an algebra $M(R, A, n)$ constructed from $A$ and $R$, and $a={a_{i,j,l}|1< i,j,l<n}$ is a family of invertible matrices over $A$, we can construct a Krull-Schmidt and abelian tensor category $mathcal C$ over $mathbb{F}$ such that $R$ is the Green ring of $mathcal C$ and $A$ is the Auslander algebra of $mathcal C$. In this case, $mathcal C$ has finitely many indecomposable objects (up to isomorphisms) and finite dimensional Hom-spaces. Moreover, we will give a necessary and sufficient condition for such two tensor categories to be tensor equivalent.
We develop some basic concepts in the theory of higher categories internal to an arbitrary $infty$-topos. We define internal left and right fibrations and prove a version of the Grothendieck construction and of Yonedas lemma for internal categories.