Discrete and Continuous Models and Applied Computational ScienceDiscrete and Continuous Models and Applied Computational Science2658-46702658-7149Peoples' Friendship University of Russia2470410.22363/2658-4670-2020-28-3-230-251Research ArticleAsymptotic solution of Sturm-Liouville problem with periodic boundary conditions for relativistic finite-difference Schrödinger equationAmirkhanovIlkizar V.<p>Candidate of Physical and Mathemati- cal Sciences, head of the group of Methods for Solving Mathematical Physics Problems of Laboratory of Information Technologies (LIT)</p>camir@jinr.ruKolosovaIrina S.<p>PhD’s degree student of Department of Applied Probability and Informatics</p>i.se.kolosova@gmail.comVasilyevSergey A.<p>Candidate of Physical and Mathematical Sciences, assistant professor of Department of Applied Probability and Informatics</p>vasilyev-sa@rudn.ruJoint Institute for Nuclear ResearchPeoples’ Friendship University of Russia (RUDN University)1512202028323025128092020Copyright © 2020, Amirkhanov I.V., Kolosova I.S., Vasilyev S.A.2020<p>The quasi-potential approach is very famous in modern relativistic particles physics. This approach is based on the so-called covariant single-time formulation of quantum field theory in which the dynamics of fields and particles is described on a space-like three-dimensional hypersurface in the Minkowski space. Special attention in this approach is paid to methods for constructing various quasi-potentials. The quasipotentials allow to describe the characteristics of relativistic particles interactions in quark models such as amplitudes of hadron elastic scatterings, mass spectra, widths of meson decays and cross sections of deep inelastic scatterings of leptons on hadrons. In this paper SturmLiouville problems with periodic boundary conditions on a segment and a positive half-line for the 2<em>m</em>-order truncated relativistic finite-difference Schrdinger equation (LogunovTavkhelidzeKadyshevsky equation, LTKT-equation) with a small parameter are considered. A method for constructing of asymptotic eigenfunctions and eigenvalues in the form of asymptotic series for singularly perturbed SturmLiouville problems with periodic boundary conditions is proposed. It is assumed that eigenfunctions have regular and boundary-layer components. This method is a generalization of asymptotic methods that were proposed in the works of A. <em>N</em>. Tikhonov, A. B. Vasilyeva, and V. F Butuzov. We present proof of theorems that can be used to evaluate the asymptotic convergence for singularly perturbed problems solutions to solutions of degenerate problems when 0 and the asymptotic convergence of truncation equation solutions in the case <em>m</em>. In addition, the SturmLiouville problem on the positive half-line with a periodic boundary conditions for the quantum harmonic oscillator is considered. Eigenfunctions and eigenvalues</p>
<p>are constructed for this problem as asymptotic solutions for 4-order LTKT-equation.</p>asymptotic analysissingularly perturbed differential equationSturm-Liouville problemrelativistic finite-difference Schrödinger equationperiodic boundary conditionsquasi-potential approachасимптотический анализсингулярно возмущённое дифференциальное уравнениезадача Штурма-Лиувиллярелятивистское конечно-разностное уравнение Шрёдингерапериодические краевые условияквазипотенциальный подход<p>Introduction The relativistic finite-difference analog of the Schrdinger equation (Logunov-Tavkhelidze-Kadyshevsky equation, LTK-equation) with the quasi- potential in the relativistic configurational space for the radial wave functions of bound states for two identical elementary particles without spin has the form [1]-[13]: rad [</p>[A. A. Atanasov and A. T. 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