Conjecture on higher normalized eigenvalues of the projective plane

Let Λk(RP2)\Lambda_k(\mathbb{RP}^2) denote the supremum of the normalized kk-th Laplace eigenvalue over metrics on the real projective plane. A sequence of metrics is said to degenerate to a touching union when it converges to a configuration of components meeting at points. Projective-plane eigenvalue conjecture. For every k1k\geqslant 1,

Λk(RP2)=4π(2k+1).\Lambda_k(\mathbb{RP}^2)=4\pi(2k+1).

For k2k\geqslant 2, the supremum cannot be attained by a smooth metric and is realized in the limit by a sequence degenerating to a union of k1k-1 identical round spheres and a standard projective plane touching one another, with the ratio of the area of the projective plane to the area of each sphere equal to 3:23:2. This extends the known value Λ2(RP2)=20π\Lambda_2(\mathbb{RP}^2)=20\pi and predicts the degeneration pattern for all higher indices.

Sources & referencesView supporting material

Primary source

Mikhail Karpukhin, Nikolai Nadirashvili, Alexei V. Penskoi and Iosif Polterovich, “An isoperimetric inequality for Laplace eigenvalues on the sphere”, arXiv:1706.05713 (2019).

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