Does there existIf $\Gamma\subseteq SL(n,\mathbb{R})$ is a lattice in $SL(n,\mathbb{R})$ which(i.e. discrete and finite covolume), does not$\Gamma$ necessarily contain anysome $\mathbb{R}$-diagonalizable copy of $\mathbb{Z}^{n-1}$ ? I
I know that the answer is noyes if the lattice is supposed to be uniformcocompact, and that $SL(n,\mathbb{Z})$ also satisfies this property, that the answer is whyalso yes in the case $\Gamma=SL(n,\mathbb Z)$. So I wonder if every lattice satisfies this property.