Bass–Quillen conjecture


In mathematics, the Bass-Quillen conjecture relates vector bundles over a regular Noetherian ring A and over the polynomial ring. The conjecture is named for Hyman Bass and Daniel Quillen, who formulated the conjecture.

Statement of the conjecture

The conjecture is a statement about finitely generated projective modules. Such modules are also referred to as vector bundles. For a ring A, the set of isomorphism classes of vector bundles over A of rank r is denoted by.
The conjecture asserts that for a regular Noetherian ring A the assignment
yields a bijection

Known cases

If A = k is a field, the Bass–Quillen conjecture asserts that any projective module over is free. This question was raised by Jean-Pierre Serre and was later proved by Quillen and Suslin, see Quillen–Suslin theorem.
More generally, the conjecture was shown by in the case that A is a smooth algebra over a field k. Further known cases are reviewed in.

Extensions

The set of isomorphism classes of vector bundles of rank r over A can also be identified with the nonabelian cohomology group
Positive results about the homotopy invariance of
of isotropic reductive groups G have been obtained by by means of A1 homotopy theory.