Dr. Timo Keller

Contact

Lehrstuhl für Computeralgebra
Mathematisches Institut
Universität Bayreuth
Universitätsstraße 30
95440 Bayreuth, Germany

Office: building NW II, room 3.2.02.737
Phone: +49 (0)921 55 3384
E-Mail: public GPG key
Workgroup: Prof. Dr. Michael Stoll
Chair: Mathematik II (computational arithmetic geometry)
Office hours: by appointment

Research

Arithmetic geometry, especially arithmetic and computational aspects of Jacobian and abelian varieties over arithmetic fields, their rational points, L-functions, cohomology and the Birch-Swinnerton-Dyer conjecture:

• over number fields: explicit methods for modular abelian varieties, their Galois representations, Selmer and Shafarevich-Tate groups, Heegner points, Euler systems, p-adic L-functions (funded by the DFG)
• in positive characteristic: theoretical aspects of abelian varieties and schemes over higher dimensional bases over finitely generated fields, their L-functions, Shafarevich-Tate groups, Brauer groups, étale, flat and p-adic cohomologies

Publications

Published

• On an Analogue of the Conjecture of Birch and Swinnerton-Dyer for Abelian Schemes over Higher Dimensional Bases over Finite Fields ^DOI abstract
  We formulate an analogue of the conjecture of Birch and Swinnerton-Dyer for Abelian schemes with everywhere good reduction over higher dimensional bases over finite fields of characteristic $p$. We prove the prime-to-$p$ part conditionally on the finiteness of the $p$-primary part of the Tate-Shafarevich group or the equality of the analytic and the algebraic rank. If the base is a product of curves, Abelian varieties and K3 surfaces, we prove the prime-to-$p$ part of the conjecture for constant or isoconstant Abelian schemes, in particular the prime-to-$p$ part for (1) relative elliptic curves with good reduction or (2) Abelian schemes with constant isomorphism type of $\Acal[p]$ or (3) Abelian schemes with supersingular generic fibre, and the full conjecture for relative elliptic curves with good reduction over curves and for constant Abelian schemes over arbitrary bases. We also reduce the conjecture to the case of surfaces as the basis.
  
  Doc. Math. 24 (2019), 915–993
• A duality theorem for Tate–Shafarevich groups of curves over algebraically closed fields ^{DOI PDF} abstract
  In this note, we prove a duality theorem for the Tate-Shafarevich group of a finite discrete Galois module over the function field $K$ of a curve over an algebraically closed field: There is a perfect duality of finite groups $\Sha^1(K,F) \times \Sha^1(K,F') \to \Q/\Z$ for $F$ a finite étale Galois module on $K$ of order invertible in $K$ and with $F' = \Hom(F,\Q/\Z(1))$. Furthermore, we prove that $\H^1(K,G) = 0$ for $G$ a simply connected, quasisplit semisimple group over $K$ not of type $E_8$.
  
  Abh. Math. Semin. Univ. Hambg. (2018) 88(2), 289–295
• On the Tate-Shafarevich group of Abelian schemes over higher dimensional bases over finite fields ^{DOI PDF} abstract
  We study analogues for the Tate-Shafarevich group for Abelian schemes with everywhere good reduction over higher dimensional bases over finite fields.
  
  manuscripta math. (2016) 150(1–2), 211–245

Preprints

• On an Analogue of the Conjecture of Birch and Swinnerton-Dyer for Abelian Schemes over Higher Dimensional Bases over Finite Fields – complements, 2020
• Transfer of quadratic forms and their Stiefel-Whitney invariants, 2020

Activities

Oberseminar Arithmetische Geometrie

Thursday, 10:15–12:00 (Homepage)

Kleine AG/Bayerische Arbeitsgemeinschaft

Kleine/Bayerische Arbeitsgemeinschaft »Algebraische Geometrie und Zahlentheorie«