In differential geometry, a field in mathematics, a multivector field, polyvector field of degree ', or '-vector field, on a smooth manifold , is a generalization of the notion of a vector field on a manifold.
A multivector field of degree ' is a global section of the kth exterior power of the tangent bundle, i.e. assigns to each point it assigns a -vector in .
The set of all multivector fields of degree ' on is denoted by or by .
The set of multivector fields is an -vector space for every ', so that is a graded vector space.
Furthermore, there is a wedge product
which for ' and ' recovers the standard action of smooth functions on vector fields. Such product is associative and graded commutative, making into a graded commutative algebra.
Similarly, the Lie bracket of vector fields extends to the so-called Schouten-Nijenhuis bracket
which is -bilinear, graded skew-symmetric and satisfies the graded version of the Jacobi identity. Furthermore, it satisfies a graded version of the Leibniz identity, i.e. it is compatible with the wedge product, making the triple into a Gerstenhaber algebra.
Since the tangent bundle is dual to the cotangent bundle, multivector fields of degree ' are dual to '-forms, and both are subsumed in the general concept of a tensor field, which is a section of some tensor bundle, often consisting of exterior powers of the tangent and cotangent bundles. A -tensor field is a differential -form, a -tensor field is a vector field, and a -tensor field is -vector field.
While differential forms are widely studied as such in differential geometry and differential topology, multivector fields are often encountered as tensor fields of type , except in the context of the geometric algebra (see also Clifford algebra).