B4.4

Differentiable Manifolds
Part II, 2003

Define the 'pull-back' homomorphism of differential forms determined by the smooth map f:MNf: M \rightarrow N and state its main properties.

If θ:WV\theta: W \rightarrow V is a diffeomorphism between open subsets of Rm\mathbb{R}^{m} with coordinates xix_{i} on VV and yjy_{j} on WW and the mm-form ω\omega is equal to fdx1dxmf d x_{1} \wedge \ldots \wedge d x_{m} on VV, state and prove the expression for θ(ω)\theta^{*}(\omega) as a multiple of dy1dymd y_{1} \wedge \ldots \wedge d y_{m}.

Define the integral of an mm-form ω\omega over an oriented mm-manifold MM and prove that it is well-defined.

Show that the inclusion map f:NMf: N \hookrightarrow M, of an oriented nn-submanifold NN (without boundary) into MM, determines an element ν\nu of Hn(M)Hom(Hn(M),R)H_{n}(M) \cong \operatorname{Hom}\left(H^{n}(M), \mathbb{R}\right). If M=N×PM=N \times P and f(x)=(x,p)f(x)=(x, p), for xNx \in N and pp fixed in PP, what is the relation between ν\nu and π([ωN])\pi^{*}\left(\left[\omega_{N}\right]\right), where [ωN]\left[\omega_{N}\right] is the fundamental cohomology class of NN and π\pi is the projection onto the first factor?