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E_7, Wirtinger inequalities, Cayley 4-form, and homotopy

Victor Bangert·Mikhail G. Katz·Steven Shnider·Shmuel Weinberger
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Abstract

We study optimal curvature-free inequalities of the type discovered by C. Loewner and M. Gromov, using a generalisation of the Wirtinger inequality for the comass. Using a model for the classifying space BS^3 built inductively out of BS^1, we prove that the symmetric metrics of certain two-point homogeneous manifolds turn out not to be the systolically optimal metrics on those manifolds. We point out the unexpected role played by the exceptional Lie algebra E_7 in systolic geometry, via the calculation of Wirtinger constants. Using a technique of pullback with controlled systolic ratio, we calculate the optimal systolic ratio of the quaternionic projective plane, modulo the existence of a Joyce manifold with Spin(7) holonomy and unit middle-dimensional Betti number.

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Victor Bangert, Mikhail G. Katz, Steven Shnider, Shmuel Weinberger. 2008-01-03. E_7, Wirtinger inequalities, Cayley 4-form, and homotopy. https://arxiv.org/abs/math/0608006

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