Associated bundles in restriction category world
In classical differential geometry, principal bundles are locally the cartesian product of a manifold and a group, vector bundles are locally the cartesian product of a manifold and a vector space. It is a classical result that there is a one to one correspondance between the category of principal -bundles and the category of vector bundles with fiber .
In [1] Cockett and Cruttwell generalized vector bundles as differential bundles in tangent categories. In [2], Cockett and I generalized principal bundles to restriction categories and in particular to tangent restriction categories.
Does the correspondance between principal and vector bundles hold up in this generalized setup?
It does not. I will give an example of a restriction category in which there are more differential bundles than principal bundles. However one direction of the correspondance still holds. The construction that sends a principal bundle to a vector bundle is known as the associated bundle. We will perform this construction in the setting of tangent restriction categories, obtain a functor and describe its properties. This does not just recover a classical result from differential geometry, it also provides a strategy for constructing examples of differential bundles in tangent restriction categories.
- [1] J. R. B. Cockett and G. S. H. Cruttwell, Differential structure, tangent structure, and SDG, Applied Categorical Structures 22 (2014), 331–417.
- [2] R. Cockett and F. Schwarz, Lie groups in tangent join restriction categories, preprint arXiv:2509.18410,2025