Title: On the topology of $\mathcal{M}_{0,n+1}/Σ_n$ and $\overline{\mathcal{M}}_{0,n+1}/Σ_n$

Abstract: This paper contains some results about the topology of $\mathcal{M}_{0,n+1}/\Sigma_n$ and $\overline{\mathcal{M}}_{0,n+1}/\Sigma_n$, where $\mathcal{M}_{0,n+1}$ is the moduli space of genus zero Riemann surfaces with marked points and $\overline{\mathcal{M}}_{0,n+1}$ is its Deligne-Mumford compactification. We show that $\mathcal{M}_{0,n+1}/\Sigma_n$ and $\overline{\mathcal{M}}_{0,n+1}/\Sigma_n$ are not topological manifolds for $n\geq 4$, and they are simply connected for any $n\in\mathbb{N}$. We also present some homology computations: for example we show that the homology of $\mathcal{M}_{0,n+1}/\Sigma_n$ is all torsion and that $\mathcal{M}_{0,p+1}/\Sigma_p$ has no $p$ torsion, where $p$ is a prime. Lastly we compute $H_*(\mathcal{M}_{0,n+1}/\Sigma_n;\mathbb{Z})$ for small values of $n$, proving that $\mathcal{M}_{0,n+1}/\Sigma_n$ is contractible for $n\leq 5$ while $\mathcal{M}_{0,7}/\Sigma_6$ is not.