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The special linear group $\operatorname{SL}(n,\mathbb{R})$ of degree $n$ over $\mathbb{R}$ is the set of $n \times n$ matrices with determinant $1$, with the group operations of ordinary matrix multiplication and matrix inversion. We denote by $\operatorname{SL}(n,\mathbb{Z})$ the group of $n \times n$ matrices with integer entries and determinant equals 1. Note that $\operatorname{SL}(n,\mathbb{Z})$ is a discrete subgroup of $\operatorname{SL}(n,\mathbb{R})$.

Let $G$ to be a topological group and $H$ to be a subgroup of $G$. We will say that a regular Borel measure $\mu$ on the quotient $G/H$ is a left invariant Haar measure if for all Borel sets $E \subseteq G/H$ and all $g \in G$ we have $\mu(gE) = \mu(E)$.

If $G$ is a locally compact Hausdorff group and $\Gamma$ is a discrete subgroup such that $G/H$ carries a finite left G-invariant Harr measure, then we say that $\Gamma$ is a $\textbf{lattice}$ in $G$.

We have the following results:

  1. $\operatorname{SL}(n,\mathbb{Z})$ is a lattice in $\operatorname{SL}(n,\mathbb{R})$. Moreover, the quotiont $\operatorname{SL}(n,\mathbb{R})/\operatorname{SL}(n,\mathbb{Z})$ is not compact.

  2. (Mahler Criterion) For a sequnece $(g_{m})_{m\in \mathbb{N}}$ of $\operatorname{SL}(n,\mathbb{R})$, the sequence $(\pi (g_{m}))_{m\in \mathbb{N}}$ of $\operatorname{SL}(n,\mathbb{R})/\operatorname{SL}(n, \mathbb{Z})$ does not have a convergent subsequence if, and only if, there exists a sequence $v_{m} \in \mathbb{Z}^{n}$ with $v_{m} \neq 0$ such that $g_{m}(v_{m})$ tends to $0$.

where $\pi\colon\operatorname{SL}(n,\mathbb{R}) \to \operatorname{SL}(n,\mathbb{R})/\operatorname{SL}(n,\mathbb{Z})$ is the natural projection.

The second result suggest to me that $\operatorname{SL}(n,\mathbb{R})/\operatorname{SL}(n, \mathbb{Z})$ is a Hausdorff space, but I can't find any reference. So, I do not know if it is true.

Thanks

Samuel Adrian Antz
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    The action of any discrete subgroup on the ambient (locally compact Hausdorff) topological group is always properly discontinuous. https://math.stackexchange.com/questions/3186183/left-translation-on-lie-group-of-a-discrete-subgroup-is-properly-discontinuous – Moishe Kohan Apr 15 '19 at 23:37
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    More generally for any topological group $G$ and closed subgroup $H$ the quotient $G/H$ is Hausdorff. See https://math.stackexchange.com/questions/2787022/quotient-of-a-topological-group-by-a-closed-subgroup-is-hausdorff – YCor Apr 16 '19 at 19:29
  • Thanks. But how to show that $H$ is closed in $G$ if $H$ is a discrete subgroup of $G$? – Pedro do Norte Apr 16 '19 at 20:53
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    https://math.stackexchange.com/questions/29515/why-is-every-discrete-subgroup-of-a-hausdorff-group-closed – Moishe Kohan Apr 16 '19 at 23:23

1 Answers1

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To summarize the comments: Combining Left translation on Lie group of a discrete subgroup is properly discontinuous, Quotient of a topological group by a closed subgroup is Hausdorff, Why is every discrete subgroup of a Hausdorff group closed?

answers your question in affirmative: The quotient is Hausdorff.

Moishe Kohan
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