Birkhoff–Grothendieck theorem explained
In mathematics, the Birkhoff–Grothendieck theorem classifies holomorphic vector bundles over the complex projective line. In particular every holomorphic vector bundle over
is a direct sum of holomorphic
line bundles. The theorem was proved by, and is more or less equivalent to
Birkhoff factorization introduced by .
Statement
More precisely, the statement of the theorem is as the following.
on
is holomorphically isomorphic to a direct sum of line bundles:
l{E}\congl{O}(a1) ⊕ … ⊕ l{O}(an).
The notation implies each summand is a Serre twist some number of times of the trivial bundle. The representation is unique up to permuting factors.
Generalization
The same result holds in algebraic geometry for algebraic vector bundle over
for any field
.It also holds for
with one or two orbifold points, and for chains of projective lines meeting along nodes.
Applications
One application of this theorem is it gives a classification of all coherent sheaves on
. We have two cases, vector bundles and coherent sheaves supported along a subvariety, so
where n is the degree of the fat point at
. Since the only subvarieties are points, we have a complete classification of coherent sheaves.
See also
Further reading
- Book: 10.1007/978-3-0348-0151-5. Vector Bundles on Complex Projective Spaces . 1980 . Okonek . Christian . Schneider . Michael . Spindler . Heinz . 978-3-0348-0150-8 . Modern Birkhäuser Classics . Birkhäuser Basel.
- Tournaments, Flags, and Harmonic Maps . Mathematische Annalen . 1987 . 277 . 249–266 . Salamon . S. M. . Burstall . F. E. . 2 . 10.1007/BF01457363 . 120270501 .
External links
