## Particle-like structure of Lie algebras.(English)Zbl 1422.17008

Summary: If a Lie algebra structure $$\mathbf{\mathfrak{g}}$$ on a vector space is the sum of a family of mutually compatible Lie algebra structures $$\mathbf{\mathfrak{g}}_i$$’s, we say that $$\mathbf{\mathfrak{g}}$$ is simply assembled from the $$\mathbf{\mathfrak{g}}_i$$’s. Repeating this procedure with a number of Lie algebras, themselves simply assembled from the $$\mathbf{\mathfrak{g}}_i$$’s, one obtains a Lie algebra assembled in two steps from $$\mathbf{\mathfrak{g}}_i$$’s, and so on. We describe the process of modular disassembling of a Lie algebra into a unimodular and a non-unimodular part. We then study two inverse questions: which Lie algebras can be assembled from a given family of Lie algebras, and from which Lie algebras can a given Lie algebra be assembled. We develop some basic assembling and disassembling techniques that constitute the elements of a new approach to the general theory of Lie algebras. The main result of our theory is that any finite-dimensional Lie algebra over an algebraically closed field of characteristic zero or over $$\mathbb{R}$$ can be assembled in a finite number of steps from two elementary constituents, which we call dyons and triadons. Up to an abelian summand, a dyon is a Lie algebra structure isomorphic to the non-abelian 2-dimensional Lie algebra, while a triadon is isomorphic to the 3-dimensional Heisenberg Lie algebra. As an example, we describe constructions of classical Lie algebras from triadons.{