Friday, 20 August 2010

dg.differential geometry - A question about a one-form on Riemannian manifold

Assuming the dimension of M is at least 2 (otherwise it's false), you can do the following. Let p1,p2,dots be isolated points where X does not vanish but where you want omega to vanish. In a neighborhood Ui of each pi, there are coordinates (x1,dots,xn) centered at pi on which X has the coordinate representation X=partial/partialx1. In each Ui, let omegai=dx2+|x|2dx1. Then let U0 be the complement of {p1,p2,dots}, and let omega0=Xflat (the 1-form dual to X via the metric). Let {phi0,phii} be a partition of unity subordinate to the cover {U0,Ui}, and let omega=sumige0phiiomegai. The fact that omegai(X)>0 at points other than pi and zeros of X ensures that omega(X) vanishes only at such points.

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