We consider Fock's fundamental theory of the hydrogen atom in momentum space, which allows a realization of the previously predicted rotation group of a three-dimensional (3D) sphere in four-dimensional (4D) space. We then modify Fock's theory and abandon the momentum-space description. To transform and simplify the theory, we use invariant tensor methods of electrostatics in 3D and 4D spaces. We find a coordinate 4D space where the Schrödinger equation becomes the 4D Laplace equation. The transition from harmonic 4D polynomials to the original 3D physical space is algebraic and involves derivatives with respect to a coordinate that is interpreted as time. We obtain a differential equation for eigenfunctions in the momentum space and find its solutions. A concise calculation of the quadratic Stark effect is given. The Schwinger resolvent is derived by the method of harmonic polynomials. Ladder operators are also considered.

Keywords: Fock's theory, quantum Coulomb problem, harmonic operators, transformation to coordinate space PACS: 02.30.Em, 03.65.Db, 03.65.Ge (all) DOI: 10.3367/UFNe.2021.04.038966 URL: https://ufn.ru/en/articles/2022/9/c/ 001099189500003 2-s2.0-85163414158 2022PhyU...65..952E Citation: Efimov S P "Coordinate space modification of Fock's theory. Harmonic tensors in the quantum Coulomb problem" Phys. Usp. 65 952–967 (2022) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Received: 3rd, April 2021, accepted: 19th, April 2021 Оригинал: Ефимов С П «Трансформация теории Фока в координатное пространство. Гармонические тензоры в квантовой задаче Кулона» УФН 192 1019–1034 (2022); DOI: 10.3367/UFNr.2021.04.038966