# Solvmanifold

In mathematics, a solvmanifold is a homogeneous space of a connected solvable Lie group. It may also be characterized as a quotient of a connected solvable Lie group by a closed subgroup. (Some authors also require that the Lie group be simply-connected, or that the quotient be compact.) A special class of solvmanifolds, nilmanifolds, was introduced by Malcev, who proved the first structural theorems. Properties of general solvmanifolds are similar, but somewhat more complicated.

## Properties

• A solvmanifold is diffeomorphic to the total space of a vector bundle over some compact solvmanifold. This statement was conjectured by G. Mostow and proved by L. Auslander and R. Tolimieri.
• The fundamental group of an arbitrary solvmanifold is polycyclic.
• A compact solvmanifold is determined up to diffeomorphism by its fundamental group.
• Fundamental groups of compact solvmanifolds may be characterized as group extensions of free abelian groups of finite rank by finitely generated torsion-free nilpotent groups.
• Every solvmanifold is aspherical. Among all compact homogeneous spaces, solvmanifolds may be characterized by the properties of being aspherical and having a solvable fundamental group.

## Completeness

Let ${\displaystyle {\mathfrak {g}}}$ be a real Lie algebra. It is called a complete Lie algebra if each map

ad${\displaystyle (X):{\mathfrak {g}}\to {\mathfrak {g}},X\in {\mathfrak {g}}}$

in its adjoint representation is hyperbolic, i.e. has real eigenvalues. Let G be a solvable Lie group whose Lie algebra ${\displaystyle {\mathfrak {g}}}$ is complete. Then for any closed subgroup Γ of G, the solvmanifold G/Γ is a complete solvmanifold.