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1. The Kodaira dimension of complex hyperbolic manifolds with cusps

   https://doi.org/10.1112/S0010437X1700762X  

   Bakker, Benjamin; Tsimerman, Jacob (March 2018, Compositio Mathematica)

   We prove a bound relating the volume of a curve near a cusp in a complex ball quotient $$X=\mathbb{B}/\unicode[STIX]{x1D6E4}$$ to its multiplicity at the cusp. There are a number of consequences: we show that for an $$n$$ -dimensional toroidal compactification $$\overline{X}$$ with boundary $$D$$ , $$K_{\overline{X}}+(1-\unicode[STIX]{x1D706})D$$ is ample for $$\unicode[STIX]{x1D706}\in (0,(n+1)/2\unicode[STIX]{x1D70B})$$ , and in particular that $$K_{\overline{X}}$$ is ample for $$n\geqslant 6$$ . By an independent algebraic argument, we prove that every ball quotient of dimension $$n\geqslant 4$$ is of general type, and conclude that the phenomenon famously exhibited by Hirzebruch in dimension 2 does not occur in higher dimensions. Finally, we investigate the applications to the problem of bounding the number of cusps and to the Green–Griffiths conjecture. 

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2. L-spaces, taut foliations, and graph manifolds

   https://doi.org/10.1112/S0010437X19007814  

   Hanselman, Jonathan; Rasmussen, Jacob; Rasmussen, Sarah Dean; Watson, Liam (March 2020, Compositio Mathematica)

   null (Ed.)

   If $$Y$$ is a closed orientable graph manifold, we show that $$Y$$ admits a coorientable taut foliation if and only if $$Y$$ is not an L-space. Combined with previous work of Boyer and Clay, this implies that $$Y$$ is an L-space if and only if $$\unicode[STIX]{x1D70B}_{1}(Y)$$ is not left-orderable. 

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3. THE DE BRUIJN–NEWMAN CONSTANT IS NON-NEGATIVE

   https://doi.org/10.1017/fmp.2020.6  

   RODGERS, BRAD; TAO, TERENCE (January 2020, Forum of Mathematics, Pi)

   For each $$t\in \mathbb{R}$$ , we define the entire function $$\begin{eqnarray}H_{t}(z):=\int _{0}^{\infty }e^{tu^{2}}\unicode[STIX]{x1D6F7}(u)\cos (zu)\,du,\end{eqnarray}$$ where $$\unicode[STIX]{x1D6F7}$$ is the super-exponentially decaying function $$\begin{eqnarray}\unicode[STIX]{x1D6F7}(u):=\mathop{\sum }_{n=1}^{\infty }(2\unicode[STIX]{x1D70B}^{2}n^{4}e^{9u}-3\unicode[STIX]{x1D70B}n^{2}e^{5u})\exp (-\unicode[STIX]{x1D70B}n^{2}e^{4u}).\end{eqnarray}$$ Newman showed that there exists a finite constant $$\unicode[STIX]{x1D6EC}$$ (the de Bruijn–Newman constant ) such that the zeros of $$H_{t}$$ are all real precisely when $$t\geqslant \unicode[STIX]{x1D6EC}$$ . The Riemann hypothesis is equivalent to the assertion $$\unicode[STIX]{x1D6EC}\leqslant 0$$ , and Newman conjectured the complementary bound $$\unicode[STIX]{x1D6EC}\geqslant 0$$ . In this paper, we establish Newman’s conjecture. The argument proceeds by assuming for contradiction that $$\unicode[STIX]{x1D6EC}<0$$ and then analyzing the dynamics of zeros of $$H_{t}$$ (building on the work of Csordas, Smith and Varga) to obtain increasingly strong control on the zeros of $$H_{t}$$ in the range $$\unicode[STIX]{x1D6EC} 

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4. THE DYNAMICAL MORDELL–LANG CONJECTURE FOR ENDOMORPHISMS OF SEMIABELIAN VARIETIES DEFINED OVER FIELDS OF POSITIVE CHARACTERISTIC

   https://doi.org/10.1017/S1474748019000318  

   Corvaja, Pietro; Ghioca, Dragos; Scanlon, Thomas; Zannier, Umberto (March 2021, Journal of the Institute of Mathematics of Jussieu)

   null (Ed.)

   Abstract Let $$K$$ be an algebraically closed field of prime characteristic $$p$$ , let $$X$$ be a semiabelian variety defined over a finite subfield of $$K$$ , let $$\unicode[STIX]{x1D6F7}:X\longrightarrow X$$ be a regular self-map defined over $$K$$ , let $$V\subset X$$ be a subvariety defined over $$K$$ , and let $$\unicode[STIX]{x1D6FC}\in X(K)$$ . The dynamical Mordell–Lang conjecture in characteristic $$p$$ predicts that the set $$S=\{n\in \mathbb{N}:\unicode[STIX]{x1D6F7}^{n}(\unicode[STIX]{x1D6FC})\in V\}$$ is a union of finitely many arithmetic progressions, along with finitely many $$p$$ -sets, which are sets of the form $$\{\sum _{i=1}^{m}c_{i}p^{k_{i}n_{i}}:n_{i}\in \mathbb{N}\}$$ for some $$m\in \mathbb{N}$$ , some rational numbers $$c_{i}$$ and some non-negative integers $$k_{i}$$ . We prove that this conjecture is equivalent with some difficult diophantine problem in characteristic 0. In the case $$X$$ is an algebraic torus, we can prove the conjecture in two cases: either when $$\dim (V)\leqslant 2$$ , or when no iterate of $$\unicode[STIX]{x1D6F7}$$ is a group endomorphism which induces the action of a power of the Frobenius on a positive dimensional algebraic subgroup of $$X$$ . We end by proving that Vojta’s conjecture implies the dynamical Mordell–Lang conjecture for tori with no restriction. 

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5. Almost Mathieu operators with completely resonant phases

   https://doi.org/10.1017/etds.2018.133  

   LIU, WENCAI (July 2020, Ergodic Theory and Dynamical Systems)

   Let $$\unicode[STIX]{x1D6FC}\in \mathbb{R}\backslash \mathbb{Q}$$ and $$\unicode[STIX]{x1D6FD}(\unicode[STIX]{x1D6FC})=\limsup _{n\rightarrow \infty }(\ln q_{n+1})/q_{n}<\infty$$ , where $$p_{n}/q_{n}$$ is the continued fraction approximation to $$\unicode[STIX]{x1D6FC}$$ . Let $$(H_{\unicode[STIX]{x1D706},\unicode[STIX]{x1D6FC},\unicode[STIX]{x1D703}}u)(n)=u(n+1)+u(n-1)+2\unicode[STIX]{x1D706}\cos 2\unicode[STIX]{x1D70B}(\unicode[STIX]{x1D703}+n\unicode[STIX]{x1D6FC})u(n)$$ be the almost Mathieu operator on $$\ell ^{2}(\mathbb{Z})$$ , where $$\unicode[STIX]{x1D706},\unicode[STIX]{x1D703}\in \mathbb{R}$$ . Avila and Jitomirskaya [The ten Martini problem. Ann. of Math. (2), 170 (1) (2009), 303–342] conjectured that, for $$2\unicode[STIX]{x1D703}\in \unicode[STIX]{x1D6FC}\mathbb{Z}+\mathbb{Z}$$ , $$H_{\unicode[STIX]{x1D706},\unicode[STIX]{x1D6FC},\unicode[STIX]{x1D703}}$$ satisfies Anderson localization if $$|\unicode[STIX]{x1D706}|>e^{2\unicode[STIX]{x1D6FD}(\unicode[STIX]{x1D6FC})}$$ . In this paper, we develop a method to treat simultaneous frequency and phase resonances and obtain that, for $$2\unicode[STIX]{x1D703}\in \unicode[STIX]{x1D6FC}\mathbb{Z}+\mathbb{Z}$$ , $$H_{\unicode[STIX]{x1D706},\unicode[STIX]{x1D6FC},\unicode[STIX]{x1D703}}$$ satisfies Anderson localization if $$|\unicode[STIX]{x1D706}|>e^{3\unicode[STIX]{x1D6FD}(\unicode[STIX]{x1D6FC})}$$ . 

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