Analytically solvable Hamiltonian in invariant subspaces Antonio Sérgio Magalhães de Castro, Roberto Grimaudo, Davide Valenti, Agostino Migliore, Hiromichi Nakazato and Antonino Messina Eur. Phys. J. Plus, 138 8 (2023) 766 Published online: 29 August 2023 DOI: 10.1140/epjp/s13360-023-04375-6