1,361,481 research outputs found
On higher-order discriminants
For the family of polynomials in one variable , , we consider its higher-order discriminant sets , where Res, , ,
, and their projections in the spaces of the variables . Set , . We show that
Res, where ,
Res if and
, Res if . The equation defines the projection in the space of the
variables of the closure of the set of values of for
which and have two distinct roots in common. The polynomials
are irreducible. The result is generalized
to the case when is replaced by a polynomial , for
On the minimization of Dirichlet eigenvalues of the Laplace operator
We study the variational problem \inf \{\lambda_k(\Omega): \Omega\
\textup{open in}\ \R^m,\ |\Omega| < \infty, \ \h(\partial \Omega) \le 1 \},
where is the 'th eigenvalue of the Dirichlet Laplacian
acting in , \h(\partial \Omega) is the - dimensional
Hausdorff measure of the boundary of , and is the Lebesgue
measure of . If , and , then there exists a convex
minimiser . If , and if is a minimiser,
then is also a
minimiser, and is connected. Upper bounds are
obtained for the number of components of . It is shown that if
, and then has at most components.
Furthermore is connected in the following cases : (i) (ii) and (iii) and (iv) and
. Finally, upper bounds on the number of components are obtained for
minimisers for other constraints such as the Lebesgue measure and the torsional
rigidity.Comment: 16 page
The aspherical Cavicchioli-Hegenbarth-Repovš generalized Fibonacci groups
The Cavicchioli–Hegenbarth–Repovš generalized Fibonacci groups are defined by the presentations Gn (m, k) = 〈x 1, … , xn | xixi+m = xi+k (1 ⩽ i ⩽ n)〉. These cyclically presented groups generalize Conway's Fibonacci groups and the Sieradski groups. Building on a theorem of Bardakov and Vesnin we classify the aspherical presentations Gn (m, k). We determine when Gn (m, k) has infinite abelianization and provide sufficient conditions for Gn (m, k) to be perfect. We conjecture that these are also necessary conditions. Combined with our asphericity theorem, a proof of this conjecture would imply a classification of the finite Cavicchioli–Hegenbarth–Repovš groups
The frequency of elliptic curve groups over prime finite fields
Letting vary over all primes and vary over all elliptic curves over
the finite field , we study the frequency to which a given group
arises as a group of points . It is well-known that the
only permissible groups are of the form . Given such a candidate group, we let be
the frequency to which the group arises in this way. Previously, the
second and fourth named authors determined an asymptotic formula for
assuming a conjecture about primes in short arithmetic
progressions. In this paper, we prove several unconditional bounds for
, pointwise and on average. In particular, we show that
is bounded above by a constant multiple of the expected quantity
when and that the conjectured asymptotic for holds for
almost all groups when . We also apply our
methods to study the frequency to which a given integer arises as the group
order .Comment: 40 pages, with an appendix by Chantal David, Greg Martin and Ethan
Smith. Final version, to appear in the Canad. J. Math. Major reorganization
of the paper, with the addition of a new section, where the main results are
summarized and explaine
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