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Teichmüller Discs with Completely Degenerate Kontsevich-Zorich Spectrum

We reduce a question of Eskin-Kontsevich-Zorich and Forni-Matheus-Zorich, which asks for a classification of all $\text{SL}_2(\mathbb{R})$-invariant ergodic probability measures with completely degenerate Kontsevich-Zorich spectrum, to a conjecture of Möller's. Let $\mathcal{D}_g (1)$ be the subset of the moduli space of Abelian differentials $\mathcal{M}_g$ whose elements have period matrix derivative of rank one. There is an $\text{SL}_2(\mathbb{R})$-invariant ergodic probability measure $ν$ with completely degenerate Kontsevich-Zorich spectrum, i.e. $λ_1 = 1 > λ_2 = \cdots = λ_g = 0$, if and only if $ν$ has support contained in $\mathcal{D}_g (1)$. We approach this problem by studying Teichmüller discs contained in $\mathcal{D}_g (1)$. We show that if $(X,ω)$ generates a Teichmüller disc in $\mathcal{D}_g (1)$, then $(X,ω)$ is completely periodic. Furthermore, we show that there are no Teichmüller discs in $\mathcal{D}_g (1)$, for $g = 2$, and the two known examples of Teichmüller discs in $\mathcal{D}_g (1)$, for $g = 3, 4$, are the only two such discs in those genera. Finally, we prove that if there are no genus five Veech surfaces generating Teichmüller discs in $\mathcal{D}_5(1)$, then there are no Teichmüller discs in $\mathcal{D}_g (1)$, for $g = 5,6$.