Guivarc’h, Y.; Starkov, A. N. Orbits of linear group actions, random walks on homogeneous spaces and toral automorphisms. (English) Zbl 1050.37012 Ergodic Theory Dyn. Syst. 24, No. 3, 767-802 (2004). Let \(\Gamma\subset \text{GL}(V)\) be a group of linear maps on a finite-dimensional real vector space \(V\). By analogy with the case \(\text{SL}(n,\mathbb{Z})\subset \text{GL}(n,\mathbb{R})\), a vector \(v\) is called \(\Gamma\)-irrational if \(0\) is a limit point of the orbit \(\Gamma v\subset V\). The main result in this paper gives rather general conditions on \(\Gamma\) that guarantee the orbit closure of a \(\Gamma\)-irrational vector is large. Precisely, assume that the identity component \(G\) of the Zariski closure of \(\Gamma\) is a semisimple Lie group, and let \(v\) be a \(\Gamma\)-irrational vector. Then there exists a non-zero vector \(u\) and a connected abelian subgroup \(H\subset G\) comprising semisimple elements such that the dimension of \(H\) is the real rank of \(G\) and \(0\in\overline{Hu}\subset\overline{\Gamma v}\).The results here unify and strengthen several other results in the literature, and provide inter alia a partial solution to a problem posed by G. Margulis [in: Arnold, V. (ed.) et al., Mathematics: frontiers and perspectives. Providence, RI: American Mathematical Society (AMS), 161–174 (2000; Zbl 0952.22005)], by showing that if \(\Gamma\subset \text{GL}(n,\mathbb{Z})\) is a semigroup for which the corresponding \(G\) is semisimple and \(Q\)-irreducible on \(\mathbb{R}^n\), then any orbit of \(\Gamma\) is either finite or dense. Reviewer: Thomas Ward (Norwich) Cited in 23 Documents MSC: 37C85 Dynamics induced by group actions other than \(\mathbb{Z}\) and \(\mathbb{R}\), and \(\mathbb{C}\) 60B11 Probability theory on linear topological spaces Keywords:linear group action; Zariski dense; toral automorphisms Citations:Zbl 0952.22005 PDFBibTeX XMLCite \textit{Y. Guivarc'h} and \textit{A. N. Starkov}, Ergodic Theory Dyn. Syst. 24, No. 3, 767--802 (2004; Zbl 1050.37012) Full Text: DOI