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Milds # Spinor bundle

In differential geometry, given a spin structure on an $n$ -dimensional orientable Riemannian manifold $(M,g),\,$ one defines the spinor bundle to be the complex vector bundle $\pi _{\mathbf {S} }\colon {\mathbf {S} }\to M\,$ associated to the corresponding principal bundle $\pi _{\mathbf {P} }\colon {\mathbf {P} }\to M\,$ of spin frames over $M$ and the spin representation of its structure group ${\mathrm {Spin} }(n)\,$ on the space of spinors $\Delta _{n}.\,$ .

A section of the spinor bundle ${\mathbf {S} }\,$ is called a spinor field.

## Formal definition

Let $({\mathbf {P} },F_{\mathbf {P} })$ be a spin structure on a Riemannian manifold $(M,g),\,$ that is, an equivariant lift of the oriented orthonormal frame bundle $\mathrm {F} _{SO}(M)\to M$ with respect to the double covering $\rho \colon {\mathrm {Spin} }(n)\to {\mathrm {SO} }(n)$ of the special orthogonal group by the spin group.

The spinor bundle ${\mathbf {S} }\,$ is defined  to be the complex vector bundle

${\mathbf {S} }={\mathbf {P} }\times _{\kappa }\Delta _{n}\,$ associated to the spin structure ${\mathbf {P} }$ via the spin representation $\kappa \colon {\mathrm {Spin} }(n)\to {\mathrm {U} }(\Delta _{n}),\,$ where ${\mathrm {U} }({\mathbf {W} })\,$ denotes the group of unitary operators acting on a Hilbert space ${\mathbf {W} }.\,$ It is worth noting that the spin representation $\kappa$ is a faithful and unitary representation of the group ${\mathrm {Spin} }(n)$ .