Condition on a differential form arising from the theory of elasticity
Clash Royale CLAN TAG #URR8PPP up vote 8 down vote favorite 1 Let $D$ be the unit $n$-ball (for concreteness). Let $betainOmega^1(D;R^n)$ be an $R^n$-valued one-form, having full rank (viewed as a section of $T^*Dotimes R^n$). Under what conditions on $beta$, does there exist a section $Q$ of $SO(n,R)$ (over $D$), such that $Qcircbeta$ is closed (hence exact)? The question is non-trivial for the following reason: if there exist such $Q$ and an $f:Dto R^n$, such that $df = Qcircbeta$, then $beta^Tcircbeta = df^Tcirc df$, and the latter is (up to a musical isomorphism) a flat metric on $D$, whose Riemann curvature tensor vanishes. So in a sense, I have an answer to my question. What I am looking for is a more explicit condition; in particular, I wonder whether there exists a condition that is linear in $beta$. For the curious, this question came up twice in two different contexts in the theory of elasticity. dg.differential-geometry differential-forms share | cite | im...