Abstract:
Let KK be an algebraically closed field of characteristic different
from 22, gg a positive integer, f(x)f(x) a polynomial of degree 2g+12g+1
with coefficients in KK and without multiple roots,
C:y2=f(x)C:y2=f(x) the corresponding hyperelliptic curve of
genus gg over KK, and JJ its Jacobian. We identify CC with
the image of its canonical embedding in JJ (the infinite point of
CC goes to the identity element of JJ). It is well known that
for every b∈J(K) there are exactly 22g elements
a∈J(K) such that 2a=b. Stoll
constructed an algorithm that provides the Mumford representations
of all such a in terms of the Mumford representation of
b. The aim of this paper is to give explicit formulae
for the Mumford representations of all such a in terms of
the coordinates a,b, where b∈J(K) is given by a point
P=(a,b)∈C(K)⊂J(K). We also prove that if g>1,
then C(K) does not contain torsion points of orders
between 3 and 2g.
Partially supported by Simons Foundation Collaboration
grant no. 585711. I started to write this paper during my stay at
the Max-Planck-Institut für Mathematik (Bonn, Germany) in May–June
2016 and finished it during my next visit to the Institute in May–July 2018.
The MPIM hospitality and support are gratefully acknowledged.
\Bibitem{Zar19}
\by Yu.~G.~Zarhin
\paper Division by 2 on odd-degree hyperelliptic curves and their Jacobians
\jour Izv. Math.
\yr 2019
\vol 83
\issue 3
\pages 501--520
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This publication is cited in the following 13 articles:
John Boxall, “Bounds on the number of torsion points of given order on curves embedded in their jacobians”, Journal of Algebra, 2025
Christophe Levrat, “Computing the cohomology of constructible étale sheaves on curves”, Journal de théorie des nombres de Bordeaux, 36:3 (2025), 1085
G. V. Fedorov, “On Hyperelliptic Curves of Odd Degree and Genus g with Six Torsion Points of Order 2g + 1”, Dokl. Math., 2024
G. V. Fedorov, “On hyperelliptic curves of odd degree and genus g with 6 torsion points of order 2g + 1”, Doklady Rossijskoj akademii nauk. Matematika, informatika, processy upravleniâ, 518:1 (2024), 10
J. Boxall, “On the number of points of given order on odd-degree hyperelliptic curves”, Rocky Mountain J. Math., 53:2 (2023), 357–382
E. Cotterill, N. Pflueger, N. Zhang, “Weierstrass semigroups from cyclic covers of hyperelliptic curves”, Bull. Braz. Math. Soc., New Series, 54:3 (2023), 37
B. M. Bekker, Yu. G. Zarhin, “Torsion points of small order on hyperelliptic curves”, Eur. J. Math., 8:2 (2022), 611–624
J. Box, S. Gajovic, P. Goodman, “Cubic and quartic points on modular curves using generalised symmetric chabauty”, Int. Math. Res. Notices, 2022
N. Mani, S. Rubinstein-Salzedo, “Diophantine tuples over Zp”, Acta Arith., 197:4 (2021), 331–351
V. Arul, “Division by 1−ζ on superelliptic curves and Jacobians”, Int. Math. Res. Notices, 2021:4 (2021), 3143–3185
B. M. Bekker, Yu. G. Zarhin, “Torsion points of order 2G+1 on odd degree hyperelliptic curves of genus G”, Trans. Am. Math. Soc., 373:11 (2020), 8059–8094
Yu. G. Zarhin, “Halves of points of an odd degree hyperelliptic curve in its Jacobian”, Integrable systems and algebraic geometry. A celebration of Emma Previato's 65th birthday. Volume 2, Lond. Math. Soc. Lect. Note Ser., 459, Cambridge Univ. Press, Cambridge, 2020, 102–118