Past exam of the mathematics course of the University of Cambridge 2025 iii Paper 118 1 Solution Created 2026-09-24 Updated 2026-09-24
A Hermitian metric on a holomorphic vector bundle is a smoothly varying family of positive-definite Hermitian forms on its fibers. A Chern connection is a connection on a vector bundle that is compatible with and whose part is the bundle's Dolbeault partial connection, .
Choose a local holomorphic frame and write . The connection form in this frame isIf for a nowhere-zero holomorphic function , then andwhich is exactly the connection-form transformation law. The local formulas therefore define a global connection.
Identify with the tautological bundle over Complex projective space. The standard Hermitian inner product of restricts to each tautological line. On the affine chart , put for and use the holomorphic frameThenThe curvature form of a connection isConsequently Chern-Weil theory gives the closed representativewhere is the Fubini-Study form.
Past exam of the mathematics course of the University of Cambridge 2026 iii Paper 118 1 d Solution Created 2026-09-24 Updated 2026-09-24
The curvature of the Chern connection on the complex line bundle has type , and is real. Since has complex dimension one, every real two-form is a unique smooth multiple of its nonvanishing area form, sofor some real smooth function . By Chern-Weil theory,The hyperplane class has degree on a degree- plane curve, so