Projected Chern connection Created 2026-10-06 Updated 2026-10-07
If is a holomorphic subbundle of a Hermitian vector bundle , its induced Chern connection is on sections of . Orthogonal projection preserves metric compatibility, and holomorphicity of preserves the required operator. Uniqueness of the Chern connection therefore identifies the projected connection.
For a Hermitian metric on a complex manifold, the Chern connection on its holomorphic tangent bundle corresponds to a real metric-compatible connection preserving the almost complex structure. Its mixed torsion vanishes, and in holomorphic coordinates its remaining coefficients are . Symmetry in is equivalent to ; its conjugate gives . Thus zero torsion is exactly the Kähler metric condition, and then uniqueness identifies this connection with the Levi-Civita connection.
Trace of Chern curvature 2026-10-07
In a holomorphic local frame, a Hermitian metric on a holomorphic vector bundle has matrix . The trace of its Chern connection curvature is . A frame change multiplies by the squared modulus of a holomorphic unit, whose logarithm has vanishing mixed derivative. For two metrics, the quotient of their determinants is a global positive function, and the trace curvatures differ by the exterior derivative of its logarithmic -derivative.
Unitary flat holomorphic vector bundle 2026-10-14
A unitary representation of the fundamental group of a connected complex manifold gives a bundle with locally constant unitary transition matrices. Its induced flat unitary connection has part equal to its Dolbeault operator, so it is the Chern connection for the induced Hermitian metric. On a compact Riemann surface, zero curvature gives degree zero; the subbundle curvature inequality makes the bundle semistable.