2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/114647Instability of the excitation spectrum of an ordered noncollinear Heisenberg antiferromagnet (AF) with respect to spontaneous two-magnon decays is investigated. We use a spin-1/2 AF on a triangular lattice as an example and examine the characteristic long- and short wave-length features of its zero-temperature spectrum within the 1/S-approximation. The kinematic conditions are shown to be crucial for the existence of decays and for overall properties of the spectrum. The XXZ and the J-J' generalizations of the model, as well as the role of higher-order corrections are discussed.4.0 pages, 4 figures, published version + updated referenceStrongly Correlated Electronstext