Generic Morse-extrema conjecture for band functions

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Let VV be a real-valued periodic potential, let H0=−Δ+VH_0=-\Delta+V be the associated self-adjoint operator on ℓ2(Zd)\ell^2(\mathbb{Z}^d), and let λm(k)\lambda_m(k), k∈Rdk\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.

References

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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