TY CONF TI SPECTRA AND BOUND STATE OF THE ENERGY OPERATOR OF THREE-MAGNON SYSTEMS IN THE HEISENBERG MODEL IN THE TWO- AND THREE-DIMENSIONAL LATTICE KW three-magnon systems KW bound states KW Heisenberg model KW essential spectra JO OPERATOR EQUATIONS AND SOME RELATED ISSUES IN APPLIED MATHEMATICS AU Tashpulatov, S.M. PY 2026 PB FSBE Institution of Higher Education Voronezh State University of Forestry and Technologies named after G.F. Morozov