Principal investigation concerns the theory of branching solutions of nonlinear equations. The general existence theorems for bifurcation points, curves and surfaces are proved by consideration of the branching equation reduced to the canonical form with the use of combinations of analytical, topological and algebraic methods. The proof method for these theorems intensively uses the Jordan structure of a linearized problem, as well as application of the Kronecker - Poincare Index, the Morse - Conley Index and search of conditional extremum points of the definite functions corresponding to the branching equation. The method is also aplicable in the case of a vector parameter when the bifurcation points of a solution can fill in curves or surfaces. It makes it possible to construct an asymptotics of appropriate solution branches and consider their stability. The general theory is used for a problem of branching solutions of nonlinear elliptic equations classes and applications (e.g. the existence theorems are proved and the asymptotics of solutions of the Karman boundary value problem for systems with a biharmonic operator is constructed, the solutions of integral compensation equation of the theory of superconductivity are constructed, the bifurcation analysis of some problems for kinetic Vlasov-Maxwell systems which describe a behaviour of multicomponent plasma is realized.) The analysis of generating of free parameters in branching solutions of general classes of the nonlinear equations in Banach spaces is carried out on the base of the interlaced branching equations theory, constructed for this purpose. The backgrounds of the theory of iterative methods in a neighborhood of solution branch points of the nonlinear equations in Banach spaces are developed: the method of sequence of successive approximations with an explicit and implicit parametrization of branches, including most general N-stepped iterative method with the explicit indication of uniformization of branching solutions and construction of an initial approximation are offered; the methods of a regularization of calculations in a neighborhood of solution branch points ensuring uniform approximation of branching solutions are given. The basic results in the theory of differential - operator equations (ordinary and in partial derivatives) in Banach spaces with an irreversible operator in the main part are obtained: the existence theorems in linear and nonlinear cases are proved; the methods of reduction of this problem to the ordinary differential equations of the infinite order, to "scalar" integral equations, to the differential equations with a singular point are offered; the method of construction of classic and generalized solutions on the base of a Jordan structure of operator coefficients of a linearized equation is developed. More than 100 articles were published and reviewed (see some abstracts of these articles in Mathematical Review : 87a:58036; 98f:47069; 98d:35221; 96k:65042; 95c:47079; 93m:82047; 93a:47054; 92i:47077; 90m:58033; 89i:45018; 85j:34139; 85b:34072; 82a:47011 etc.)
Main publications:
N. Sidorov, D. Sidorov, A. Sinitsyn, Toward General Theory of Differential-Operator and Kinetic Models, World Scientific Series on Nonlinear Science Series A, 97, eds. Leon O Chua (University of California at Berkeley, USA), World Scientific Series, Singapore, 2020 , 496 pp
Nikolay Sidorov, Boris Loginov, et al Lyapunov-Schmidt methods in nonlinear analysis and applications, Mathematics and its Applications, 550, Kluwer Academic Publishers, Dordrecht, 2002