Solvable Lie Foliations on Compact Five-Manifolds: Classification, Cohomological Obstruction, and Non-Homogeneous Examples

Abstract

We study $\GA$-Lie foliations on compact five-manifolds. We establish a structural classification of the holonomy group $\Gamma$ into five types according to its algebraic structure inside $\GA$. For three of these types (I, II, IIIa) we prove homogeneity via Meigniez's theorem and the Matsumoto--Tsuchiya theorem. For Type~IIIb we prove non-homogeneity by exhibiting a non-polycyclic holonomy group, extending the Dathe--Ndiaye construction \cite{DN11}. We introduce a cohomological class $[F]\in H^2({\Gamma }^{\mathrm{ab}},[\Gamma ,\Gamma ])$ as a \emph{necessary} obstruction to homogeneity: if $\mathcal{F}$ is homogeneous and $\Gamma$ is polycyclic then $[F]=0$. We show that Type IIIb foliations satisfy $[F]\ne 0$. For Type IIIc, we prove that certain foliations are non-homogeneous by a direct argument when the generating translations are $\Q(λ)$-linearly independent; we exhibit explicit homogeneous examples showing that this type is \emph{not} universally non-homogeneous. Finally, we construct the first known non-homogeneous $\mathrm{Sol}$-Lie foliation in dimension five by a verified lattice deformation.