Galois representations of octahedral type and 2-coverings of elliptic curves.
Let be a finite extension of with ramification index , and let be a finite abelian -extension with Galois group and ramification index . We give a criterion in terms of the ramification numbers for a fractional ideal of the valuation ring of not to be free over its associated order . In particular, if then the inverse different can be free over its associated order only when (mod ) for all . We give three consequences of this. Firstly, if is a Hopf order and is -Galois...
In this paper, we survey some Galois-theoretic techniques for studying torsion points on curves. In particular, we give new proofs of some results of A. Tamagawa and the present authors for studying torsion points on curves with “ordinary good” or “ordinary semistable” reduction at a given prime. We also give new proofs of : (1) the Manin-Mumford conjecture : there are only finitely many torsion points lying on a curve of genus at least embedded in its jacobian by an Albanese map; and (2) the...
We construct Galois towers with good asymptotic properties over any non-prime finite field ; that is, we construct sequences of function fields = (N₁ ⊂ N₂ ⊂ ⋯) over of increasing genus, such that all the extensions are Galois extensions and the number of rational places of these function fields grows linearly with the genus. The limits of the towers satisfy the same lower bounds as the best currently known lower bounds for the Ihara constant for non-prime finite fields. Towers with these properties...
The set of all divisors of , ordered according to increasing magnitude, is considered, and an upper bound on the gaps between consecutive ones is obtained. We are especially interested in the divisors nearest and obtain a lower bound on their distance.
We study the gaps between primes in Beatty sequences following the methods in the recent breakthrough by Maynard (2015).
Assuming the Riemann hypothesis, we investigate the distribution of gaps between the zeros of . We prove that a positive proportion of gaps are less than times the average spacing and, in the other direction, a positive proportion of gaps are greater than times the average spacing. We also exhibit the existence of infinitely many normalized gaps smaller (larger) than (, respectively).