Conjecture on the cut locus of lifted Fermat hypersurfaces

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Let π:S2n+1→CPn\pi:\mathbb{S}^{2n+1}\to\mathbb{CP}^n be the quotient map, let

X(d)={[z0:z1:⋯:zn]∈CPn:∑i=0nzid=0},X(d)=\left\{[z_0:z_1:\cdots:z_n]\in\mathbb{CP}^n:\sum_{i=0}^n z_i^d=0\right\},

and set X~(d)=π−1(X(d))\tilde{X}(d)=\pi^{-1}(X(d)). Here Zd⋆(n+1)\mathbb{Z}_d^{\star(n+1)} denotes the (n+1)(n+1)-fold topological join of Zd\mathbb{Z}_d, and ×Zd\times_{\mathbb{Z}_d} denotes the diagonal action of Zd\mathbb{Z}_d. Cut-locus conjecture. The cut locus of X~(d)⊆S2n+1\tilde{X}(d)\subseteq\mathbb{S}^{2n+1} is

Zd⋆(n+1)×ZdS1.\mathbb{Z}_d^{\star(n+1)}\times_{\mathbb{Z}_d}\mathbb{S}^1.

This conjecture gives a geometric description of the cut locus of the lift of a Fermat-type complex hypersurface under the Hopf quotient. The supplied text does not state any partial results or resolution, so its status remains open.

References

Primary source

Sachchidanand Prasad, “Cut Locus of Submanifolds: A Geometric and Topological Viewpoint”, arXiv:2303.14931 (2023).

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