5,902 research outputs found
Abelian bordered factors and periodicity
A finite word u is said to be bordered if u has a proper prefix which is also
a suffix of u, and unbordered otherwise. Ehrenfeucht and Silberger proved that
an infinite word is purely periodic if and only if it contains only finitely
many unbordered factors. We are interested in abelian and weak abelian
analogues of this result; namely, we investigate the following question(s): Let
w be an infinite word such that all sufficiently long factors are (weakly)
abelian bordered; is w (weakly) abelian periodic? In the process we answer a
question of Avgustinovich et al. concerning the abelian critical factorization
theorem.Comment: 14 page
A probabilistic technique for finding almost-periods of convolutions
We introduce a new probabilistic technique for finding 'almost-periods' of
convolutions of subsets of groups. This gives results similar to the
Bogolyubov-type estimates established by Fourier analysis on abelian groups but
without the need for a nice Fourier transform to exist. We also present
applications, some of which are new even in the abelian setting. These include
a probabilistic proof of Roth's theorem on three-term arithmetic progressions
and a proof of a variant of the Bourgain-Green theorem on the existence of long
arithmetic progressions in sumsets A+B that works with sparser subsets of {1,
..., N} than previously possible. In the non-abelian setting we exhibit
analogues of the Bogolyubov-Freiman-Halberstam-Ruzsa-type results of additive
combinatorics, showing that product sets A B C and A^2 A^{-2} are rather
structured, in the sense that they contain very large iterated product sets.
This is particularly so when the sets in question satisfy small-doubling
conditions or high multiplicative energy conditions. We also present results on
structures in product sets A B. Our results are 'local' in nature, meaning that
it is not necessary for the sets under consideration to be dense in the ambient
group. In particular, our results apply to finite subsets of infinite groups
provided they 'interact nicely' with some other set.Comment: 29 pages, to appear in GAF
Building Abelian Functions with Generalised Baker-Hirota Operators
We present a new systematic method to construct Abelian functions on Jacobian
varieties of plane, algebraic curves. The main tool used is a symmetric
generalisation of the bilinear operator defined in the work of Baker and
Hirota. We give explicit formulae for the multiple applications of the
operators, use them to define infinite sequences of Abelian functions of a
prescribed pole structure and deduce the key properties of these functions. We
apply the theory on the two canonical curves of genus three, presenting new
explicit examples of vector space bases of Abelian functions. These reveal
previously unseen similarities between the theories of functions associated to
curves of the same genus
On connective KO-theory of elementary abelian 2-groups
A general notion of detection is introduced and used in the study of the
cohomology of elementary abelian 2-groups with respect to the spectra in the
Postnikov tower of orthogonal K-theory. This recovers and extends results of
Bruner and Greenlees and is related to calculations of the (co)homology of the
spaces of the associated Omega-spectra by Stong and by Cowen Morton
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