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Enriched categories, topoi, abelian categories, monoidal categories, homological algebra.

2 votes

Is the category of spherical fusion categories regular? (i.e. is image factorisation possible?)

I think the following is true, and what I was looking for. A tensor functor $F: \mathcal{C} \to \mathcal{D}$ is called dominant (sometimes called "surjective") if for any $Y: \mathcal{D}$, there is a …
Manuel Bärenz's user avatar
0 votes

Nerves of (braided or symmetric) monoidal categories

Generalising Omar's answer, braided monoidal categories are (a special case of) tricategories with one 1-morphism. Symmetric monoidal categories are tetracategories (whatever that is) with one 2-morph …
Manuel Bärenz's user avatar
2 votes
1 answer
136 views

Is the category of spherical fusion categories regular? (i.e. is image factorisation possible?)

Consider the category where objects are strict spherical fusion categories and morphisms are strict spherical functors (preserving cups and caps). I am wondering whether there is some kind of image fa …
Manuel Bärenz's user avatar
28 votes

Are dagger categories truly evil?

In my opinion, dagger categories are not evil, but they are not categories with extra structure (in the ordinary sense) either. (I think this is what Qiaochu Yuan meant in his comment.) More specifica …
Manuel Bärenz's user avatar
-1 votes

Categories of finite objects

I don't exactly understand the question, but I think you should familiarise yourself with the notion of a fully dualisable object in a (possibly higher) symmetric monoidal category. For example, a vec …
3 votes
1 answer
170 views

Pivotal functors of that are substantially different from finite group homomorphisms

Fusion categories can be seen as generalisations of the representation category of finite groups. I'm interested in spherical fusion categories. I'm trying to find "interesting" functors from a spheri …
Manuel Bärenz's user avatar
1 vote
Accepted

Pivotal functors of that are substantially different from finite group homomorphisms

I've been thinking about this since longer already and just realised a really easy example. I was a bit of a blockhead in thinking that for any inclusion functor $F$, we must have that $F\Omega_\mathc …
Manuel Bärenz's user avatar
1 vote

180˚ vs 360˚ Twists in String Diagrams for Ribbon Categories

I'm surprised nobody has mentioned Jeff Eggers "On involutive monoidal categories", which generalises Peter Selingers work, I guess. It's an excellent article, and it connects to other special cases. …
Manuel Bärenz's user avatar
0 votes
1 answer
304 views

What is the universal property of being the maximal common subobject of two objects in a sem...

Imagine a semisimple abelian category $\mathcal{C}$, for example representations of a finite group. Take two (nonsimple) objects $X, Y$ that are subobjects of a common object $Z$, and decompose them i …
Manuel Bärenz's user avatar
0 votes
Accepted

What is the universal property of being the maximal common subobject of two objects in a sem...

One can define the category of subobjects of $Z$, where the objects are subobjects of $Z$ and the morphisms have to commute with the monomorphisms of the subobjects. In this category, $S$ is simply th …
Manuel Bärenz's user avatar
2 votes

What is Yoneda's Lemma a generalization of?

Tannaka duality is essentially applying Yoneda twice. So a special case of Tannaka duality that doesn't require the Yoneda lemma would be Pontryagin duality.
2 votes
0 answers
363 views

Simplicial complexes are to PL structures of manifolds as simplicial sets are to what?

A simplicial complex is a PL structure for, and thus also homeomorphic to, a manifold if the link of every vertex is a simplicial sphere, for which there exists a definition. (I know that for high dim …
Manuel Bärenz's user avatar
13 votes
1 answer
499 views

Is there something like "Noncommutative geometry internal to a category"?

I have heard that one can do algebraic geometry internal to symmetric monoidal categories. Topological quantum field theories also exist internal to symmetric monoidal categories, and the usual defini …
Manuel Bärenz's user avatar
8 votes
0 answers
221 views

Ends and parametricity

It is well known that a set of natural transformations can be expressed as an end: $$\int_{A \in \mathcal{A}} \mathcal{B}(FA, GA) =_{\operatorname{Set}} \operatorname{Nat}(F, G)$$ This holds for func …
Manuel Bärenz's user avatar
12 votes
1 answer
527 views

Is there a "killing" lemma for G-crossed braided fusion categories?

Edit: I found a serious flaw in the question and my answer, and I had to change a lot. The basic question is still there, but the details are a lot different. Premodular categories In braided spheri …
Manuel Bärenz's user avatar

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