ISSN 2079-6900 (Print)
ISSN 2587-7496 (Online)

MSC2010 34G10

### On the invertibility of solutions of first order linear homogeneous differential equations in Banach algebras

#### O. E. Galkin1, S. Yu. Galkina2

Annotation This work is devoted to the study of some properties of linear homogeneous differential equations of the first order in Banach algebras. It is found (for some types of Banach algebras), at what right-hand side of such an equation, from the invertibility of the initial condition it follows the invertibility of its solution at any given time. Associative Banach algebras over the field of real or complex numbers are considered. The right parts of the studied equations have the form $\bigl[F(t)\bigr]\bigl(x(t)\bigr)$, where $\{F(t)\}$ is a family of bounded operators on the algebra, continuous with respect to $t\in \mathbb{R}$. The problem is to find all continuous families of bounded operators on algebra, preserving the invertibility of elements from it, for a given Banach algebra. In the proposed article, this problem is solved for only three cases. In the first case, the algebra consists of all square matrices of a given order. For this algebra, it is shown that all continuous families of operators, preserving the invertibility of elements from the algebra at zero must be of the form $[F(t)](y) = a(t)\cdot y + y\cdot b(t)$, where the families $\{a(t)\}$ and $\{b(t)\}$ are also continuous. In the second case, the algebra consists of all continuous functions on the segment. For this case, it is shown that all families of operators, preserving the invertibility of elements from the algebra at any time must be of the form $[F(t)](y) = a(t)\cdot y$, where the family $\{a(t)\}$ is also continuous. The third case concerns those Banach algebras in which all nonzero elements are invertible. For example, the algebra of complex numbers and the algebra of quaternions have this property. In this case, any continuous families of bounded operators preserves the invertibility of the elements from the algebra at any time. The proposed study is in contact with the research of the foundations of quantum mechanics. The dynamics of quantum observables is described by the Heisenberg equation. The obtained results are an indirect argument in favor of the fact, that the known form of the Heisenberg equation is the only correct one. first-order linear homogeneous differential equations in Banach algebras, preserving the invertibility of solutions

1Oleg E. Galkin, Associate Professor, Department of Applied Mathematics, National Research Lobachevsky State University of Nizhni Novgorod (pr. Gagarina, 23, Nizhni Novgorod, 603950, Russia); Senior Researcher, Laboratory of Topological Methods in Dynamics, National Research University Higher School of Economics in Nizhny Novgorod (25/12 Bolshaja Pecherskaja St., Nizhny Novgorod, 603155, Russia), Ph.D. (Physics and Mathematics), ORCID: http://orcid.org/0000-0002-1634-7792, olegegalkin@ya.ru

2Svetlana Y. Galkina, Associate Professor, Department of Fundamental Mathematics, National Research University Higher School of Economics in Nizhny Novgorod (25/12 Bolshaja Pecherskaja St., Nizhny Novgorod, 603155, Russia), Ph.D. (Physics and Mathematics), ORCID: http://orcid.org/0000-0002-2476-2275, svetlana.u.galkina@mail.ru

Citation: O. E. Galkin, S. Yu. Galkina, "[On the invertibility of solutions of first order linear homogeneous differential equations in Banach algebras]", Zhurnal Srednevolzhskogo matematicheskogo obshchestva,21:4 (2019) 430–442 (In Russian)

DOI 10.15507/2079-6900.21.201904.430-442