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A principal $G$-bundle, where $G$ denotes any topological group, is a fiber bundle $\pi :P → X$ together with a continuous right action $P × G → P$ such that $G$ preserves the fibers of $P$ and acts freely and transitively on them.

5 votes
1 answer
399 views

In what sense bibundles are called as generalized morphisms

Definition : Let $\mathcal{G}$ and $\mathcal{H}$ be Lie groupoids. A bibundle from $\mathcal{G}$ to $\mathcal{H}$ is a manifold $P$ together with two maps $a_L:P\rightarrow \mathcal{G}_0,a_R:P\righta …
Praphulla Koushik's user avatar
7 votes
3 answers
2k views

Atiyah Sequence and Connections on a Principal Bundle

Let $G$ be a Lie group and $\pi:E_G\rightarrow M $ be a principal $G$-bundle. I have seen in many places that a connection on $(E_G,M,G)$ is a splitting of the Atiyah sequence $$ 0\rightarrow \text …
Praphulla Koushik's user avatar
1 vote
0 answers
402 views

Introducing connection on principal bundle as lifting of vector field and paths

Let $\pi:P\rightarrow M$ is a principal $G$ bundle. I want to introduce the notion of connection as a way to uniquely lift the structures on $M$ to structures on $P$, namely vector fields and paths. …
Praphulla Koushik's user avatar
1 vote
0 answers
819 views

references for holomorphic principal bundles (over complex manifolds)

principal bundles in differential geometry is a classical notion and there are so many references that discuss these notion (even in text books). But, when it comes to its version in complex geometry, …
Praphulla Koushik's user avatar
1 vote
3 answers
963 views

Notion of Torsors

I am trying to read this paper by Lawrence Breen. It starts with the definition of a torsor. Let $G$ be a bundle of groups on a space $X$. The following definition of a principal space is standard, b …
Praphulla Koushik's user avatar
0 votes

Notion of Torsors

I have found the notion of group bundle in Alexandre Grothendieck's "A general theory of fibre spaces with structure sheaf". This is for my own reference and may be useful for some one who reads tha …
Praphulla Koushik's user avatar
1 vote

Atiyah Sequence and Connections on a Principal Bundle

This is from another reference. So, adding as a different answer. Appendix A "On principal bundles and Atiyah sequences" in the book Lie groupoids and Lie algebroids in differential geometry by Kiril …
Praphulla Koushik's user avatar
2 votes
0 answers
118 views

Realization of a $\mathfrak{g}$-valued $2$-form as a curvature form

Consider the Lie group $S^1$. Recall that the associated Lie algebra is $\mathbb{R}$. Let $M$ be a manifold. Consider the second de-Rham cohomology group $H^2(M,\mathbb{R})$. Let $\Omega\in H^2(M,\ …
Praphulla Koushik's user avatar
2 votes

Atiyah Sequence and Connections on a Principal Bundle

See the paper The Atiyah bundle and connections on a principal bundle by Indranil Biswas. Let $p:E_G\rightarrow M$ be a principal $G$-bundle. Michael Atiyah in his paper uses a exact sequence of vect …
Praphulla Koushik's user avatar
3 votes
1 answer
681 views

Principal bundles and fibre bundles

Let $\pi_P:P\rightarrow M$ a principal $G$ (right action) bundle. Let $F$ be a manifold with a left action of $G$. Then we have the notion of associated fibre bundle over $M$ whose fibre is $F$. I do …
Praphulla Koushik's user avatar
9 votes
6 answers
3k views

Motivation for construction of associated fiber bundle from a principal bundle

Given a principal $G$ bundle $P(M,G)$ and a manifold $F$ with an action of $G$ on it from left, we construct a fiber bundle over $M$ with fiber $F$ and call this the associated fiber bundle for $P(M,G …
Praphulla Koushik's user avatar
7 votes
1 answer
782 views

Classification of Principal $G$ bundles and vector bundles in smooth sense

Suppose $G$ is a Topological group then classification theorem of Principal $G$ bundles says that there is a Principal $G$ bundle $EG\rightarrow BG$ such that any principal $G$ bundle over a dece …
Praphulla Koushik's user avatar
2 votes
1 answer
442 views

Advantages of Atiyah sequence version of connections on a principal bundle

I am reading Lie Groupoids and Lie Algebroids in Differential Geometry by Kirill Mackenzie. In appendix (page $291$), before discussing about Atiyah sequence associated to a Principal bundle, the aut …
Praphulla Koushik's user avatar
4 votes
1 answer
278 views

Chern -Weil map for topological principal G bundles

Let $G$ be a Lie group. In the book Curvature and Characteristic classes, the author (Johan L. Dupont) mentiones in beginning of chapter 5 the following : The notion of a topological principal $ …
Praphulla Koushik's user avatar
2 votes
0 answers
133 views

Associated bundle construction and classifying space

Let $\theta:G\rightarrow H$ be a morphism of Lie groups. Given $G$ we have classifying space $BG$ and given $H$ we have classifying space $BH$. This $\theta:G\rightarrow H$ gives a map $B\theta:BG\ri …
Praphulla Koushik's user avatar

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