Generic Morse-extrema conjecture for band functions

Let VV be a real-valued periodic potential, let H0=Δ+VH_0=-\Delta+V be the associated self-adjoint operator on 2(Zd)\ell^2(\mathbb{Z}^d), and let λm(k)\lambda_m(k), kRdk\in\mathbb{R}^d, be its band functions. Generic band-extrema conjecture. Generically, with respect to the potentials and other free parameters of the operator, the extrema of the band functions satisfy: (1) they are attained by a single band; (2) they are isolated; and (3) they are nondegenerate, meaning that their Hessians are nondegenerate. The conjecture gives a precise formulation of the expectation that band functions are generically Morse functions and is relevant to spectral-band structure and applications such as homogenization and Green's function asymptotics. Statement (1), concerning attainment by a single band, was proved; the supplied status evidence does not say that statements (2) and (3) were resolved.

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Primary source

Wencai Liu, “Irreducibility of the Fermi variety for discrete periodic Schrödinger operators and embedded eigenvalues”, arXiv:2006.04733 (2021).

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