I need to cover a case of $n$dimensional locally symmetric Riemannian space of rank $n1$. Is there a simple proof that there is no such irreducible space ($n>4$)? If I need to cite the Cartan classification for that, which concrete paper/book you suggest?

1$\begingroup$ Multiply hyperbolic plane (or 2d sphere) by the Euclidean space of suitable dimension. $\endgroup$– Moishe KohanSep 17, 2020 at 3:51

$\begingroup$ @MoisheKohan yes, but what about irreducible ones? $\endgroup$– ArimakatSep 17, 2020 at 13:05

$\begingroup$ Just go through the list at en.wikipedia.org/wiki/Symmetric_space and references therein. $\endgroup$– Igor BelegradekSep 17, 2020 at 18:48
1 Answer
An irreducible symmetric space $M$ of dimension $n$ and rank $n1$ has dimension $n=2$. Indeed, the rank is the codimension of a principal orbit of the isotropy group $K$ at $p \in M$ acting on the tangent space $T_pM$. So the $K$orbits are one dimensional. Now any monoparametric subgroup of $K$ has a one dimensional orbit contained in a $2$dimensional subspace of $T_pM$ hence $K$ has a one dimensional orbit contained in a $2$dimensional subspace of $T_pM$. So $K$ has an invariant $2$dimensional subspace in $T_pM$. But $K$ is the holonomy group of $M$ at $p$ hence $K$ acts irreducibly on $T_pM$. Then $dim(T_p M)=2$.