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Topology of groups of automorphisms of surfaces, and high dimensional analogues.

7 votes

Extension of the group $Sp(2g,\mathbb{Z})$

For $g \geq 3$, the map $$H^*(Sp(2g,\mathbb{Z});\mathbb{Z}) \longrightarrow H^*(M_g;\mathbb{Z})$$ is known to be an isomorphism for $* \leq 2$. In particular, by universal coefficients the map $$H^2(S …
Oscar Randal-Williams's user avatar
6 votes

Is there Harer stability for moduli of curves with level structure?

This is not an answer to your question, but is directly related to your remark so I thought I should mention it. I have recently proved, though I am afraid that it has not appeared yet, that moduli s …
Oscar Randal-Williams's user avatar
2 votes

Mappings of mapping class groups

The second of your questions is answered in Graham Hope and Ulrike Tillmann "On the Farrell cohomology of the mapping class group of non-orientable surfaces" Proc. Amer. Math. Soc. 137 (2009), no. 1, …
Oscar Randal-Williams's user avatar
4 votes
Accepted

Elements of infinite order in the topological mapping class group

Let me suppose that $M$ is a closed manifold of dimension $d$, and let $\varphi : M \to M$ be a diffeomorphism / homeomorphism which is homotopic to the identity, and choose such a homotopy $h_t$. The …
Oscar Randal-Williams's user avatar
2 votes
Accepted

Homology dimension of the mapping class group of a surface with boundary

There is a fibration sequence $$\mathbb{S}(\Sigma_g) \to \mathcal{M}_{g}^1 \to \mathcal{M}_g$$ where $\mathcal{M}_g$ is the moduli space of Riemann surfaces, $\mathcal{M}_{g}^1$ is the moduli space of …
Oscar Randal-Williams's user avatar
2 votes

Euler class of vertical tangent bundle of the surface bundle over circle

Let me not Poincare dualise, and work in cohomology. Let me generalise the setting you have described, and consider the universal surface bundle $\pi : E \to M_g^1$ over the moduli space of surfaces w …
Oscar Randal-Williams's user avatar