24 research outputs found
The Density of a family of monogenic number fields
A monogenic polynomial is a monic irreducible polynomial with integer
coefficients which produces a monogenic number field. For a given prime ,
using the Chebotarev density theorem, we will show the density of primes ,
such that is monogenic, is bigger or equal than . We will also
prove that, when , the density of primes , which
is non-monogenic, is at least 1/9.Comment: Various corrections. Submitte
Mertens's theorem for splitting primes and more
Myriad articles are devoted to Mertens's theorem. In yet another, we merely
wish to draw attention to a proof by Hardy, which uses a Tauberian theorem of
Landau that "leads to the conclusion in a direct and elegant manner". Hardy's
proof is also quite adaptable, and it is readily combined with well-known
results from prime number theory. We demonstrate this by proving a version of
the theorem for primes in arithmetic progressions with uniformity in the
modulus, as well as a non-abelian analogue of this.Comment: This is a survey pape
On equality of ranks of local components of automorphic representations
We prove that the local components of an automorphic representation of an
adelic semisimple group have equal rank in the sense defined earlier by the
second author. Our theorem is an analogue of the results previously obtained by
Howe, Li, Dvorsky--Sahi, and Kobayashi--Savin. Unlike previous works which are
based on explicit matrix realizations and existence of parabolic subgroups with
abelian unipotent radicals, our proof works uniformly for all of the (classical
as well as exceptional) groups under consideration. Our result is an extension
of the statement known for several semisimple groups that if at least one local
component of an automorphic representation is a minimal representation, then
all of its local components are minimal.Comment: Remark 9.6 is modified. A corrigendum will also appear in
International Mathematical Research Notice
On the Erdos-Ko-Rado property for finite Groups
Let a finite group act transitively on a finite set . A subset
is said to be {\it intersecting} if for any , the
element has a fixed point. The action is said to have the {\it
weak Erd\H{o}s-Ko-Rado} property, if the cardinality of any intersecting set is
at most . If, moreover, any maximal intersecting set is a coset of a
point stabilizer, the action is said to have the {\it strong Erd\H{o}s-Ko-Rado}
property. In this paper we will investigate the weak and strong
Erd\H{o}s-Ko-Rado property and attempt to classify the groups whose all
transitive actions have these properties. In particular, we show that a group
with the weak Erd\H{o}s-Ko-Rado property is solvable and that a nilpotent group
with the strong Erd\H{o}s-Ko-Rado property is product of a -group and an
abelian group of odd order.Comment: This is the final version. To appear in the Journal of Algebraic
Combinatoric
Quasi-Random profinite groups
We will investigate quasi-randomness for profinite groups. We will obtain
bounds for the mininal degree of non-trivial representations of
and
. Our method also delivers a
lower bound for the minimal degree of a faithful representation for these
groups. Using the suitable machinery from functional analysis, we establish
exponential lower and upper bounds for the supremal measure of a product-free
measurable subset of the profinite groups and
. We also obtain analogous bounds for a special
subgroup of the automorphism group of a regular tree.Comment: This is the final version. To appear in Glasgow Mathematical Journa
On the chromatic number of structured Cayley graphs
In this paper, we will study the chromatic number of Cayley graphs of
algebraic groups that arise from algebraic constructions. Using Lang-Weil bound
and representation theory of finite simple groups of Lie type, we will
establish lower bounds on the chromatic number of these graphs. This provides a
lower bound for the chromatic number of Cayley graphs of the regular graphs
associated to the ring of matrices over finite fields. Using Weil's
bound for Kloosterman sums we will also prove an analogous result for
over finite rings.Comment: arXiv admin note: text overlap with arXiv:1507.0530
On a generalization of the Hadwiger-Nelson problem
For a field and a quadratic form defined on an -dimensional vector
space over , let , called the quadratic graph associated
to , be the graph with the vertex set where vertices form an
edge if and only if . Quadratic graphs can be viewed as natural
generalizations of the unit-distance graph featuring in the famous
Hadwiger-Nelson problem. In the present paper, we will prove that for a local
field of characteristic zero, the Borel chromatic number of
is infinite if and only if represents zero non-trivially over . The
proof employs a recent spectral bound for the Borel chromatic number of Cayley
graphs, combined with an analysis of certain oscillatory integrals over local
fields. As an application, we will also answer a variant of question 525
proposed in the 22nd British Combinatorics Conference 2009.Comment: This is the final version. Accepted in Israel Journal of Mathematic
Minimal dimension of faithful representations for -groups
For a group , we denote by , the smallest dimension of a
faithful complex representation of . Let be a non-Archimedean local
field with the ring of integers and the maximal ideal
.
In this paper, we compute the precise value of when is
the Heisenberg group over . We then use the Weil
representation to compute the minimal dimension of faithful representations of
the group of unitriangular matrices over and many
of its subgroups. By a theorem of Karpenko and Merkurjev, our result yields the
precise value of the essential dimension of the latter finite groups.Comment: Final version. To appear in "Journal of group theory
Kirillov's orbit method and polynomiality of the faithful dimension of -groups
Given a finite group and a field , the faithful dimension of
over is defined to be the smallest integer such that
embeds into . In this paper we address the
problem of determining the faithful dimension of a -group of the form
associated
to in the Lazard
correspondence, where is a nilpotent -Lie algebra
which is finitely generated as an abelian group. We show that in general the
faithful dimension of is a piecewise polynomial function of
on a partition of primes into Frobenius sets. Furthermore, we prove that for
sufficiently large, there exists a partition of by sets from
the Boolean algebra generated by arithmetic progressions, such on each part the
faithful dimension of for is equal to for a
polynomial . We show that for many naturally arising -groups,
including a vast class of groups defined by partial orders, the faithful
dimension is given by a single formula of the latter form. The arguments rely
on various tools from number theory, model theory, combinatorics and Lie
theory
Faithful representations of Chevalley groups over quotient rings of non-Archimedean local fields
Let be a non-Archimedean local field with the ring of integers
and the prime ideal and let be the adjoint Chevalley group. Let
denote the smallest possible dimension of a faithful representation of
. Using the Stone-von Neumann theorem, we determine a lower bound for
which is asymptotically the same as the results of Landazuri, Seitz
and Zalesskii for split Chevalley groups over . Our result yields
a conceptual explanation of the exponents that appear in the aforementioned
resultsComment: Final version. To appear in "Groups, Geometry, and Dynamics