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arXiv · 2404.10164

A solvable non-unitary fermionic long-range model with extended symmetry

Adel Ben Moussa·Jules Lamers·Didina Serban·Ayman Toufik
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Abstract

We define and study a long-range version of the XX model, arising as the free-fermion point of the XXZ-type Haldane--Shastry (HS) chain. It has a description via non-unitary fermions, based on the free-fermion Temperley--Lieb algebra, and may also be viewed as an alternating $\mathfrak{gl}(1|1)$ spin chain. Even and odd length behave very differently; we focus on odd length. The model is integrable, and we explicitly identify two commuting hamiltonians. While non-unitary, their spectrum is real by PT-symmetry. One hamiltonian is chiral and quadratic in fermions, while the other is parity-invariant and quartic. Their one-particle spectra have two linear branches, realising a massless relativistic dispersion on the lattice. The appropriate fermionic modes arise from 'quasi-translation' symmetry, which replaces ordinary translation symmetry. The model exhibits exclusion statistics, like the isotropic HS chain, with even more 'extended symmetry' and larger degeneracies.

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Adel Ben Moussa, Jules Lamers, Didina Serban, Ayman Toufik. 2024-04-15. A solvable non-unitary fermionic long-range model with extended symmetry. https://doi.org/10.1103/physrevlett.134.046503

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