FUNDAMENTALNAYA I PRIKLADNAYA MATEMATIKA

(FUNDAMENTAL AND APPLIED MATHEMATICS)

2000, VOLUME 6, NUMBER 3, PAGES 757-776

Roots in the universal covering group of the unimodular 2 ´ 2-matrix group

T. V. Dubrovina
N. I. Dubrovin

Abstract

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The equation $x^n=g$ has been solved in the universal covering group $\mathbb G$ of the group $\mathop{\mathrm{SL}}(2)$. If $g$ is not a central element, then the $n$-th root of $g$ exists and is unique. In the case when $g$ belongs to the center of the universal covering $\mathbb G$, the set of all solutions may be empty or may form a two-dimensional submanifold of the manifold $\mathbb G$. The following two questions are considered. (A) How wide may be this submanifold from the algebraic point of view? (B) How can we complete the group $\mathbb G$ with absent roots?

Of the results close to the main theorem one can mention the following: the semigroup $\mathop{\mathrm{SL}}(2)^+$, consisting of all matrices $A\in\mathop{\mathrm{SL}}(2)$ with non-negative coefficients, is complete, that is one can derive any root from any element.

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Last modified: December 8, 2000