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The Nielsen-Ninomiya theorem, PT-invariant non-Hermiticity and single 8-shaped Dirac cone

Abstract : The Nielsen–Ninomiya theorem implies that any local, Hermitian and translationally invariant lattice action in even-dimensional spacetime possesses an equal number of left- and right-handed chiral fermions. We argue that if one sacrifices the property of Hermiticity while keeping the locality and translation invariance, and imposing invariance of the action under the space-time (PT) reversal symmetry, then the excitation spectrum of the theory may contain a non-equal number of left- and right-handed massless fermions with real-valued dispersion. We illustrate our statement in a simple 1  +  1 dimensional lattice model which exhibits a skewed 8-figure pattern in its energy spectrum. A drawback of the model is that the PT symmetry of the Hamiltonian is spontaneously broken implying that the energy spectrum contains complex branches. We also demonstrate that the Dirac cone is robust against local disorder so that the massless excitations in this PT invariant model are not gapped by random space-dependent perturbations in the couplings.
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Contributor : Maxim Chernodub <>
Submitted on : Thursday, January 26, 2017 - 7:02:31 PM
Last modification on : Tuesday, February 23, 2021 - 3:04:02 PM

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M. N. Chernodub. The Nielsen-Ninomiya theorem, PT-invariant non-Hermiticity and single 8-shaped Dirac cone. Journal of Physics A: Mathematical and Theoretical, IOP Publishing, 2017, 50, pp.385001. ⟨10.1088/1751-8121/aa809a⟩. ⟨hal-01447422⟩



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