# Birkhoff–Grothendieck theorem

Birkhoff–Grothendieck theorem In mathematics, the Birkhoff–Grothendieck theorem classifies holomorphic vector bundles over the complex projective line. In particular every holomorphic vector bundle over {displaystyle mathbb {CP} ^{1}} is a direct sum of holomorphic line bundles. The theorem was proved by Alexander Grothendieck (1957, Theorem 2.1),[1] and is more or less equivalent to Birkhoff factorization introduced by George David Birkhoff (1909).[2] Contents 1 Statement 2 Generalization 3 Applications 4 See also 5 References 6 Further reading Statement More precisely, the statement of the theorem is as the following.

Every holomorphic vector bundle {displaystyle {mathcal {E}}} on {displaystyle mathbb {CP} ^{1}} is holomorphically isomorphic to a direct sum of line bundles: {displaystyle {mathcal {E}}cong {mathcal {O}}(a_{1})oplus cdots oplus {mathcal {O}}(a_{n}).} 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 {displaystyle mathbb {P} _{k}^{1}} for any field {displaystyle k} .[3] It also holds for {displaystyle mathbb {P} ^{1}} with one or two orbifold points, and for chains of projective lines meeting along nodes. [4] Applications One application of this theorem is it gives a classification of all coherent sheaves on {displaystyle mathbb {CP} ^{1}} . We have two cases, vector bundles and coherent sheaves supported along a subvariety, so {displaystyle {mathcal {O}}(k),{mathcal {O}}_{np}} where n is the degree of the fat point at {displaystyle x} . Since the only subvarieties are points, we have a complete classification of coherent sheaves.

See also Algebraic geometry of projective spaces Euler sequence Splitting principle K-theory Jumping line References ^ Grothendieck, Alexander (1957). "Sur la classification des fibrés holomorphes sur la sphère de Riemann". American Journal of Mathematics. 79 (1): 121–138. doi:10.2307/2372388. JSTOR 2372388. S2CID 120532002. ^ Birkhoff, George David (1909). "Singular points of ordinary linear differential equations". Transactions of the American Mathematical Society. 10 (4): 436–470. doi:10.2307/1988594. ISSN 0002-9947. JFM 40.0352.02. JSTOR 1988594. ^ Hazewinkel, Michiel; Martin, Clyde F. (1982). "A short elementary proof of Grothendieck's theorem on algebraic vectorbundles over the projective line". Journal of Pure and Applied Algebra. 25 (2): 207–211. doi:10.1016/0022-4049(82)90037-8. ^ Martens, Johan; Thaddeus, Michael (2016). "Variations on a theme of Grothendieck". Compositio Mathematica. 152: 62–98. arXiv:1210.8161. Bibcode:2012arXiv1210.8161M. doi:10.1112/S0010437X15007484. S2CID 119716554. Further reading Okonek, Christian; Schneider, Michael; Spindler, Heinz (1980). Vector Bundles on Complex Projective Spaces. Modern Birkhäuser Classics. Birkhäuser Basel. doi:10.1007/978-3-0348-0151-5. ISBN 978-3-0348-0150-8. hide vte Topics in algebraic curves Rational curves Five points determine a conicProjective lineRational normal curveRiemann sphereTwisted cubic Elliptic curves Analytic theory Elliptic functionElliptic integralFundamental pair of periodsModular form Arithmetic theory Counting points on elliptic curvesDivision polynomialsHasse's theorem on elliptic curvesMazur's torsion theoremModular elliptic curveModularity theoremMordell–Weil theoremNagell–Lutz theoremSupersingular elliptic curveSchoof's algorithmSchoof–Elkies–Atkin algorithm Applications Elliptic curve cryptographyElliptic curve primality Higher genus De Franchis theoremFaltings's theoremHurwitz's automorphisms theoremHurwitz surfaceHyperelliptic curve Plane curves AF+BG theoremBézout's theoremBitangentCayley–Bacharach theoremConic sectionCramer's paradoxCubic plane curveFermat curveGenus–degree formulaHilbert's sixteenth problemNagata's conjecture on curvesPlücker formulaQuartic plane curveReal plane curve Riemann surfaces Belyi's theoremBring's curveBolza surfaceCompact Riemann surfaceDessin d'enfantDifferential of the first kindKlein quarticRiemann's existence theoremRiemann–Roch theoremTeichmüller spaceTorelli theorem Constructions Dual curvePolar curveSmooth completion Structure of curves Divisors on curves Abel–Jacobi mapBrill–Noether theoryClifford's theorem on special divisorsGonality of an algebraic curveJacobian varietyRiemann–Roch theoremWeierstrass pointWeil reciprocity law Moduli ELSV formulaGromov–Witten invariantHodge bundleModuli of algebraic curvesStable curve Morphisms Hasse–Witt matrixRiemann–Hurwitz formulaPrym varietyWeber's theorem Singularities AcnodeCrunodeCuspDelta invariantTacnode Vector bundles Birkhoff–Grothendieck theoremStable vector bundleVector bundles on algebraic curves This topology-related article is a stub. You can help Wikipedia by expanding it.

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