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Splitting the Madsen-Tillmann Spectra MTθ_n

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arxiv 2503.10507 v1 pith:JELKUUFT submitted 2025-03-13 math.AT

Splitting the Madsen-Tillmann Spectra MTθ_n

classification math.AT
keywords madsen-tillmannmathbbprovesigmaspectrathetaaccomplishadams
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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We prove that the Madsen-Tillmann spectrum $MT\theta_n$ splits into the sum of spectra $\Sigma^{-2n}MO\langle n+1 \rangle \oplus \Sigma^{\infty-2n}\mathbb{R} P^\infty_{2n}$ after Postnikov trunctation $\tau_{\leq \ell}$ for $\ell = \lfloor \frac{n}{2} \rfloor - 6$. To accomplish this, we prove that the connecting map in a certain fiber sequence is nullhomotopic in this range by an Adams filtration argument. As an application, we compute $H_2(B\operatorname{Diff}(W^{2n}_{g},D^{2n});\mathbb{Z})$ up to extensions for $n \geq 16$ and $g \geq 7$.

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