Immersions in a Quaternionic Grassmannian inducing a given 4-form

Let $Gr_k(\H^n)$ be the Grassmannian manifold of Quaternionic $k$-planes in $\H^n$ and let $γ^n_k\to Gr_k(\H^n)$ denote the Stiefel bundle of quaternionic $k$-frames in $\H^n$. Let $σ$ denote the first symplectic Pontrjagin form associated with the universal connection on $γ^n_k$. We show that every 4-form $ω$ on a smooth manifold $M$ can be induced from $σ$ by a smooth immersion $f:M\to Gr_k(\H^n)$ (for sufficiently large $k$ and $n$) provided there exists a continuous map $f_0:M\to Gr_k(\H^n)$ which pulls back the cohomology class of $σ$ onto that of $ω$.

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