TY JOUR TI St¨uckelberg particle in external magnetic field. The method of projective operators KW St¨uckelberg particle KW magnetic field KW projective operators KW Fedorov– Gronskiy method KW exact solutions KW bound states JO Proceedings of the Komi Science Centre of the Ural Division of the Russian Academy of Sciences AU Ovsiyuk, E.M. AU Safronov, A.P. AU Ivashkevich, A.V. AU Semenyuk, O.A. PY 2022 IS 0 PB FSBI FIC "Komi Scientific Center of the Ural Branch of the Russian Academy of Sciences"