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"Gerbe" is a construct in homological algebra and topology. They can be seen as a generalization of principal bundles to the setting of 2-categories. "Gerbe" is a French (and archaic English) word that literally means wheat sheaf. Gerbes were introduced by Jean Giraud (Giraud 1971) following ideas of Alexandre Grothendieck as a tool for non-commutative cohomology in degree 2.

3 votes
1 answer
242 views

Crossed modules in context of gerbes

Question : How does Crossed modules comes into the set up of gerbes. I am reading notes on 1- and 2-gerbes by Lawrence Breen. Once he defines torsors, he introduces notion of crossed modules. … As gerbes are seen as elements of third cohomology class here, I am expecting that understanding about crossed modules in same setup as that of gerbes might give better idea of gerbes. …
Praphulla Koushik's user avatar
4 votes
1 answer
372 views

Is a gerbe over a manifold is a special case of a gerbe over a stack?

There is a notion of Gerbe over a Manifold and a notion of Gerbe over a stack. Given a manifold $M$, there is a way to associate a stack $\underline{M}$ with it and this gives an embedding of cat …
Praphulla Koushik's user avatar
1 vote
0 answers
438 views

Trivializations of gerbes as generalisation of trivializations of line bundles

I understood gerbes as generalization of line bundle here. In this, I am trying to understand how to generalize notion of trivialization of line bundle to the notion of trivialization of gerbes. … In case of gerbes it has to be on $1$ fold intersection extra i.e., $f_{\alpha\beta}:U_\alpha\cap U_\beta\rightarrow S^1$. …
Praphulla Koushik's user avatar
2 votes
2 answers
402 views

Cohomological description of gerbes over stacks

basically in gerbe territory (for smooth manifolds) if any one of the following is being considered a cohomology class in $H^3(X,\mathbb{Z})$ ** ** In similar manner, When reading about gerbes … Can some one give me some outline of how and what cohomology comes in when studying about gerbes over stacks? …
Praphulla Koushik's user avatar
2 votes
1 answer
588 views

Confusion in definition of Gerbes in Hitchin's notes

I am reading Nigel Hitchin's notes to understand about gerbes. … To understand gerbes, we need to consider the other creatures in a hierarchy to which gerbes belong, and here the lowest form of life consists of circle valued functions $f:X\rightarrow S^1$. …
Praphulla Koushik's user avatar
6 votes
2 answers
331 views

Cocycle description of gerbes

I am trying to understand cocycle description of gerbes as in https://arxiv.org/pdf/math/0611317.pdf. …
Praphulla Koushik's user avatar
11 votes
0 answers
1k views

What is there in the book Cohomologie non abélienne by Jean Giraud

These days I am trying to understand about stacks and gerbes. Most of the articles that has something to do with gerbes cite this work Cohomologie non abélienne by Jean Giraud. …
6 votes
1 answer
632 views

Connection on a Principal bundle and transition functions, as in Hitchin's notes

This is along the lines of this question Gerbes are not just topological objects: we can do differential geometry with them too. We shall next describe what a connection on a gerbe is. …
Praphulla Koushik's user avatar
3 votes
2 answers
570 views

Understanding definition of gerbe over a stack

I am reading Differentiable Stacks and Gerbes by Kai Behrend and Ping Xu. They define gerbe over a stack as follows. Let $\mathfrak{X}$ be a differentiable stack. …
Praphulla Koushik's user avatar
2 votes
1 answer
224 views

Central extension gives a gerbe over stack

Consider a central extension of Lie groups $1\rightarrow S^1\rightarrow \hat{G}\xrightarrow{\pi} G\rightarrow 1$. I understand that this mean $\pi:\hat{G}\rightarrow G$ is a surjective homomorphism o …
Praphulla Koushik's user avatar
2 votes
0 answers
58 views

Lie groupoid $G$ extensions and principal $\text{Out}(G)$ bundles over Lie groupoids

I am reading the paper Non abelian differentiable gerbes by C. Laurent-Gengoux et.al. …
Praphulla Koushik's user avatar
3 votes
1 answer
267 views

Examples of of gerbe over stacks in terms of manifolds

I am looking for some examples of gerbes over stacks (as defined in Understanding definition of gerbe over a stack) that comes from manifolds. …
Praphulla Koushik's user avatar
7 votes
3 answers
992 views

How should one think about the band of a gerbe?

I have had a look at the notes on 1-gerbes and 2-gerbes by Lawrence Breen. Question : How should one think about the band of a gerbe? …
Praphulla Koushik's user avatar
7 votes
1 answer
1k views

Understanding the definition of $G$-gerbe

In Differentiable Stacks and Gerbes Kai Behrend and Ping Xu defines an $S^1$-gerbe as the following. …
Praphulla Koushik's user avatar
5 votes
0 answers
437 views

Roadmap to understand gerbe in the sense of Lurie’s Higher Topos Theory

Definition $7.2.2.20$ : Let $\mathfrak{X} $ be an $\infty$-topos. An $n$-gerbe on $\mathfrak{X}$ is an object in $\mathfrak{X}$ which is $n$-connective and $n$-truncated. Above is the definition …
Praphulla Koushik's user avatar

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