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Global topology of the Hitchin system - GEOM

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Cohomology <strong>of</strong> ˆ Ň<br />

The cohomologies H ∗ (N d ), H ∗ (Ň d ) and H ∗ ( ˆN d ) are well<br />

understood.<br />

[Harder–Narasimhan 1975] obtained recursive formulae for<br />

#N (Fq) ❀ formula for Betti numbers via <strong>the</strong> Weil<br />

conjectures [Deligne 1974]<br />

[Atiyah–Bott 1981] gave different gauge-<strong>the</strong>oretic pro<strong>of</strong><br />

Theorem (Harder–Narasimhan, 1975)<br />

The finite group Γ acts trivially on H ∗ (Ň d ).<br />

In particular H ∗ (Ň d ) ∼ = H ∗ ( ˆN d ).<br />

pro<strong>of</strong> by showing #Ň d (Fq) = # ˆN d (Fq)<br />

[<strong>Hitchin</strong>, 1987] ⇒ false for moduli space <strong>of</strong> SL2 Higgs<br />

bundles ❀ non-triviality <strong>of</strong> our topological mirror tests<br />

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