A solvable non-unitary fermionic long-range model with extended symmetry
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 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.
Cite
@article{arxiv.2404.10164,
title = {A solvable non-unitary fermionic long-range model with extended symmetry},
author = {Adel Ben Moussa and Jules Lamers and Didina Serban and Ayman Toufik},
journal= {arXiv preprint arXiv:2404.10164},
year = {2025}
}
Comments
v1: 6+23 pages, 3 figs, 1 table. v2: various minor improvements; 6+27 pages, 1+3 figs, 1 table. v3: further impovements, 6+28 pages, 1+3 figs, 1 table. v4: accepted for publication