Yunqing Tang E-mail:  yunqing.tang at berkeley dot edu I am an associate professor at University of California, Berkeley and I joined Berkeley as an assistant professor in July 2022. I graduated from Harvard University under supervision of Mark Kisin. Here is my CV.

Research articles

• Infinitely many primes of basic reduction for some abelian fourfolds, with Wanlin Li, Elena Mantovan, and Rachel Pries, preprint.
  For certain abelian fourfolds, we proved that they have infinitely many basic reduction primes.


• Arithmetic holonomy bounds and effective Diophantine approximation, with Frank Calegari and Vesselin Dimitrov, to appear in the ICM proceedings.
  We explore servaral threads in Diophantine approximation using further developments of our arithmetic holonomy bound in our irrationality paper.


• Positive density of primes of ordinary reduction for abelian varieties of simple signature, with Victoria Cantoral-Farfan, Wanlin Li, Elena Mantovan, and Rachel Pries, submitted.
  We prove that for some abelian variety with its endomorphism algebra being a CM field and simple signature, it admits a density one set of mu-ordinary reductions.


• The linear independence of 1, zeta(2), L(2,chi_{-3}), with Frank Calegari and Vesselin Dimitrov, submitted.
  We prove the Q-linear independence of 1, the value of Riemann zeta function at 2, and the value at 2 of the Dirichlet L-function associated to the quadratic character with conductor -3 using rational approximations constructed by Zagier.


• The unbounded denominators conjecture, with Frank Calegari and Vesselin Dimitrov, Journal of the American Mathematical Society 38 (2025), 627–702.
  We prove the unbounded denominators conjecture in the theory of noncongruence modular forms.


• Picard ranks of K3 surfaces over function fields and the Hecke orbit conjecture, with Davesh Maulik and Ananth Shankar, Inventiones Mathematicae 228 (2022), no. 3, 1075–1143.
  We prove the any generically ordinary projective curve in GSpin Shimura varieties mod p admits infinitely mamy points on the union of special divisors; moreover, we use this result to deduce a special case of the Hecke orbit conjecture of Chai and Oort.


• Exceptional jumps of Picard ranks of reductions of K3 surfaces over number fields, with Ananth Shankar, Arul Shankar, and Salim Tayou, Forum of Mathematics, Pi. 10 (2022), E21.
  Given a K3 surface X over a number field K, we prove that the set of primes of K where the geometric Picard rank jumps is infinite, assuming that X has everywhere potentially good reduction.


• Reductions of abelian surfaces over global function fields, with Davesh Maulik and Ananth Shankar, Compositio Mathematica 158 (2022), no. 4, 893–950.
  For a non-isotrivial ordinary abelian surface A over a global function field with good reduction everywhere, we prove that under mild conditions, there are infinitely many places modulo which A is isogenous to the product of two elliptic curves.


• Newton polygon stratification of the Torelli locus in PEL-type Shimura varieties, with Wanlin Li, Elena Mantovan, and Rachel Pries, International Mathematics Research Notices 2022, no. 9, 6464-6511.
  We develop a clutching method to show that the intersection of the Torelli locus with some Newton strata in certain PEL-type Shimura varieties is non-empty with applications to Moonen's families and unlikely intersection of Torelli locus with certain Newton strata in A_g.


• Exceptional splitting of reductions of abelian surfaces, with Ananth Shankar, Duke Mathematical Journal 169 (2020), no. 3, 397–434.
  We prove that an abelian surface with real multiplication over a number field has infinitely many places of geometrically nonsimple reduction.


• Newton polygons arising for special families of cyclic covers of the projective line, with Wanlin Li, Elena Mantovan, and Rachel Pries, Research in Number Theory 5 (2019), no. 1, Paper No. 12, 31 pp.
  We produce multiple new examples of Newton polygons and Ekedahl–Oort types of Jacobians of smooth curves in characteristic p from twenty special families of curves in Moonen's work.


• Newton polygons of cyclic covers of the projective line branched at three points, with Wanlin Li, Elena Mantovan, and Rachel Pries, Research Directions in Number Theory: Women in Numbers IV pp. 115-132.
  We produce multiple new examples of Newton polygons that occur for Jacobians of smooth curves in characteristic p from such cyclic covers.


• Effective bounds for Brauer groups of Kummer surfaces over number fields, with Victoria Cantoral-Farfan, Sho Tanimoto, and Erik Visse, Journal of the London Mathematical Society Volume 97, Issue 3 (2018), pp. 353-376
  We study effective bounds for Brauer groups of Kummer surfaces associated to Jacobians of genus 2 curves defined over number fields.


• Cycles in the de Rham cohomology of abelian varieties over number fields, Compositio Mathematica 154 (2018), no.4, pp. 850--882.
  We prove the conjecture of Ogus that absolute Tate cycles are the same as Hodge cycles for some classes of abelian varieties.


• Algebraic solutions of differential equations over the projective line minus three points, International Journal of Number Theory Volume No.14, Issue No. 05 (2018), pp. 1427–1457.
  We prove a variant of the Grothendieck--Katz p-curvature conjecture under certain convergence condition for all finite places.

Survey article

• Reductions of abelian varieties and K3 surfaces, with Ananth Shankar, Proceedings of the Second JNT Biennial Conference
  This article is a survey of joint work with Davesh Maulik, Ananth Shankar, Arul Shankar, and Salim Tayou on arithmetic intersection theory on GSpin Shimura varieties with applications to abelian varieties, K3 surfaces, and the ordinary Hecke orbit conjecture.