TY JOUR TI St¨uckelberg particle in external magnetic field. Nonrelativistic approximation. Exact solutions KW St¨uckelberg particle KW nonrelativistic approximation KW magnetic field KW projective operators 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"