More Like this

1. Filtration and splitting of the Hodge bundle on the nonvarying strata of quadratic differentials

   https://doi.org/10.1090/tran/9416  

   Chen, Dawei; Yu, Fei (March 2025, Transactions of the American Mathematical Society)

   We describe the Harder–Narasimhan filtration of the Hodge bundle for Teichmüller curves in the nonvarying strata of quadratic differentials appearing in the work of Dawei Chen and Martin Möller [Ann. Sci. ’Ec. Norm. Sup’er. (4) 47 (2014), pp. 309–369]. Moreover, we show that the Hodge bundle on the nonvarying strata away from the irregular components can split as a direct sum of line bundles. As applications, we determine all individual Lyapunov exponents of algebraically primitive Teichmüller curves in the nonvarying strata and derive new results regarding the asymptotic behavior of Lyapunov exponents. 

   more » « less
2. Newton Polygon Stratification of the Torelli Locus in Unitary Shimura Varieties

   https://doi.org/10.1093/imrn/rnaa306  

   Li, Wanlin; Mantovan, Elena; Pries, Rachel; Tang, Yunqing (December 2020, International Mathematics Research Notices)

   null (Ed.)

   Abstract We study the intersection of the Torelli locus with the Newton polygon stratification of the modulo $$p$$ reduction of certain Shimura varieties. We develop a clutching method to show that the intersection of the open Torelli locus with some Newton polygon strata is non-empty. This allows us to give a positive answer, under some compatibility conditions, to a question of Oort about smooth curves in characteristic $$p$$ whose Newton polygons are an amalgamate sum. As an application, we produce infinitely many new examples of Newton polygons that occur for smooth curves that are cyclic covers of the projective line. Most of these arise in inductive systems that demonstrate unlikely intersections of the open Torelli locus with the Newton polygon stratification in Siegel modular varieties. In addition, for the 20 special Shimura varieties found in Moonen’s work, we prove that all Newton polygon strata intersect the open Torelli locus (if $p>>0$ in the supersingular cases). 

   more » « less
3. Nonvarying, affine and extremal geometry of strata of differentials

   https://doi.org/10.1017/S0305004123000567  

   CHEN, DAWEI (October 2023, Mathematical Proceedings of the Cambridge Philosophical Society)

   Abstract We prove that the nonvarying strata of abelian and quadratic differentials in low genus have trivial tautological rings and are affine varieties. We also prove that strata ofk-differentials of infinite area are affine varieties for allk. Vanishing of homology in degree higher than the complex dimension follows as a consequence for these affine strata. Moreover we prove that the stratification of the Hodge bundle for abelian and quadratic differentials of finite area is extremal in the sense that merging two zeros in each stratum leads to an extremal effective divisor in the boundary. A common feature throughout these results is a relation of divisor classes in strata of differentials as well as its incarnation in Teichmüller dynamics. 

   more » « less
4. Moduli Spaces of Quadratic Maps: Arithmetic and Geometry

   https://doi.org/10.1093/imrn/rnae126  

   Ramadas, Rohini (June 2024, International Mathematics Research Notices)

   Abstract We establish an implication between two long-standing open problems in complex dynamics. The roots of the $$n$$th Gleason polynomial $$G_{n}\in{\mathbb{Q}}[c]$$ comprise the $$0$$-dimensional moduli space of quadratic polynomials with an $$n$$-periodic critical point. $$\operatorname{Per}_{n}(0)$$ is the $$1$$-dimensional moduli space of quadratic rational maps on $${\mathbb{P}}^{1}$$ with an $$n$$-periodic critical point. We show that if $$G_{n}$$ is irreducible over $${\mathbb{Q}}$$, then $$\operatorname{Per}_{n}(0)$$ is irreducible over $${\mathbb{C}}$$. To do this, we exhibit a $${\mathbb{Q}}$$-rational smooth point on a projective completion of $$\operatorname{Per}_{n}(0)$$, using the admissible covers completion of a Hurwitz space. In contrast, the Uniform Boundedness Conjecture in arithmetic dynamics would imply that for sufficiently large $$n$$, $$\operatorname{Per}_{n}(0)$$ itself has no $${\mathbb{Q}}$$-rational points. 

   more » « less
5. Limit sets of Teichmüller geodesics with minimal nonuniquely ergodic vertical foliation, II

   https://doi.org/10.1515/crelle-2017-0024  

   Brock, Jeffrey; Leininger, Christopher; Modami, Babak; Rafi, Kasra (January 2020, Journal für die reine und angewandte Mathematik (Crelles Journal))

   null (Ed.)

   Abstract Given a sequence of curves on a surface, we provide conditions which ensure that (1) the sequence is an infinite quasi-geodesic in the curve complex, (2) the limit in the Gromov boundary is represented by a nonuniquely ergodic ending lamination, and (3) the sequence divides into a finite set of subsequences, each of which projectively converges to one of the ergodic measures on the ending lamination. The conditions are sufficiently robust, allowing us to construct sequences on a closed surface of genus g for which the space of measures has the maximal dimension {3g-3} , for example. We also study the limit sets in the Thurston boundary of Teichmüller geodesic rays defined by quadratic differentials whose vertical foliations are obtained from the constructions mentioned above. We prove that such examples exist for which the limit is a cycle in the 1-skeleton of the simplex of projective classes of measures visiting every vertex. 

   more » « less