10,963 research outputs found
On polarised class groups of orders in quartic CM-fields
We give an explicit necessary condition for pairs of orders in a quartic
CM-field to have the same polarised class group. This generalises a simpler
result for imaginary quadratic fields. We give an application of our results to
computing endomorphism rings of abelian surfaces over finite fields, and we use
our results to extend a completeness result of Murabayashi and Umegaki to a
list of abelian surfaces over the rationals with complex multiplication by
arbitrary orders.Comment: 19 pages, v2 strengthened results slightly and changed theorem
numbering, v3 further strengthened results and added more details, v4 eased
the presentation but changed notations and numbering, v5 updated references,
v6 removes mistaken "transitivity" statemen
Isogeny graphs with maximal real multiplication
An isogeny graph is a graph whose vertices are principally polarized abelian
varieties and whose edges are isogenies between these varieties. In his thesis,
Kohel described the structure of isogeny graphs for elliptic curves and showed
that one may compute the endomorphism ring of an elliptic curve defined over a
finite field by using a depth first search algorithm in the graph. In dimension
2, the structure of isogeny graphs is less understood and existing algorithms
for computing endomorphism rings are very expensive. Our setting considers
genus 2 jacobians with complex multiplication, with the assumptions that the
real multiplication subring is maximal and has class number one. We fully
describe the isogeny graphs in that case. Over finite fields, we derive a depth
first search algorithm for computing endomorphism rings locally at prime
numbers, if the real multiplication is maximal. To the best of our knowledge,
this is the first DFS-based algorithm in genus 2
Sato-Tate groups of genus 2 curves
We describe the analogue of the Sato-Tate conjecture for an abelian variety
over a number field; this predicts that the zeta functions of the reductions
over various finite fields, when properly normalized, have a limiting
distribution predicted by a certain group-theoretic construction related to
Hodge theory, Galois images, and endomorphisms. After making precise the
definition of the "Sato-Tate group" appearing in this conjecture, we describe
the classification of Sato-Tate groups of abelian surfaces due to
Fite-Kedlaya-Rotger-Sutherland. (These are notes from a three-lecture series
presented at the NATO Advanced Study Institute "Arithmetic of Hyperelliptic
Curves" held in Ohrid (Macedonia) August 25-September 5, 2014, and are expected
to appear in a proceedings volume.)Comment: 20 pages; includes custom class file; v2: formula of Birch correcte
The Infrastructure of a Global Field of Arbitrary Unit Rank
In this paper, we show a general way to interpret the infrastructure of a
global field of arbitrary unit rank. This interpretation generalizes the prior
concepts of the giant step operation and f-representations, and makes it
possible to relate the infrastructure to the (Arakelov) divisor class group of
the global field. In the case of global function fields, we present results
that establish that effective implementation of the presented methods is indeed
possible, and we show how Shanks' baby-step giant-step method can be
generalized to this situation.Comment: Revised version. Accepted for publication in Math. Com
On the structure of the Galois group of the maximal pro- extension with restricted ramification over the cyclotomic -extension
Let be the cyclotomic -extension of an algebraic
number field . We denote by a finite set of prime numbers which does not
contain , and the set of primes of lying above .
In the present paper, we will study the structure of the Galois group
of the maximal pro- extension unramified outside
over . We mainly consider the question whether
is a non-abelian free pro- group or not. In the
former part, we treat the case when is an imaginary quadratic field and (here is an odd prime number which does not split in ). In
the latter part, we treat the case when is a totally real field and .Comment: 20 pages, changed several places, added sentences and reference
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