12,915 research outputs found
On a question of Bumagin and Wise
Motivated by a question of Bumagin and Wise, we construct a continuum of
finitely generated, residually finite groups whose outer automorphism groups
are pairwise non-isomorphic finitely generated, non-recursively-presentable
groups. These are the first examples of such residually finite groups.Comment: 8 page
Every group is the outer automorphism group of an HNN-extension of a fixed triangle group
Fix an equilateral triangle group
with arbitrary. Our main result is: for every presentation
of every countable group there exists an HNN-extension
of such that . We construct the HNN-extensions explicitly, and examples are given. The
class of groups constructed have nice categorical and residual properties. In
order to prove our main result we give a method for recognising malnormal
subgroups of small cancellation groups, and we introduce the concept of
"malcharacteristic" subgroups.Comment: 39 pages. Final version, to appear in Advances in Mathematic
On the outer automorphism groups of finitely generated, residually finite groups
Bumagin-Wise posed the question of whether every countable group can be
realised as the outer automorphism group of a finitely generated, residually
finite group. We give a partial answer to this problem for recursively
presentable groups.Comment: 13 pages. Final versio
The Outer Automorphism Groups of Two-Generator One-Relator Groups with Torsion
The main result of this paper is a complete classification of the outer
automorphism groups of two-generator, one-relator groups with torsion. To this
classification we apply recent algorithmic results of Dahmani--Guirardel, which
yields an algorithm to compute the isomorphism class of the outer automorphism
group of a given two-generator, one-relator group with torsion.Comment: 15 pages, final version. To appear in Proc. Amer. Math. So
Magnetic properties of the Anderson model: a local moment approach
We develop a local moment approach to static properties of the symmetric
Anderson model in the presence of a magnetic field, focussing in particular on
the strong coupling Kondo regime. The approach is innately simple and
physically transparent; but is found to give good agreement, for essentially
all field strengths, with exact results for the Wilson ratio, impurity
magnetization, spin susceptibility and related properties.Comment: 7 pages, 3 postscript figues. Latex 2e using the epl.cls Europhysics
Letters macro packag
Whoa, Nellie! Empirical Tests of College Football's Conventional Wisdom
College football fans, coaches, and observers have adopted a set of beliefs about how college football poll voters behave. I document three pieces of conventional wisdom in college football regarding the timing of wins and losses, the value of playing strong opponents, and the value of winning by wide margins. Using a unique data set with 25 years of AP poll results, I test college football's conventional wisdom. In particular, I test (1) whether it is better to lose early or late in the season, (2) whether teams benefit from playing stronger opponents, and (3) whether teams are rewarded for winning by large margins. Contrary to conventional wisdom, I find that (1) it is better to lose later in the season than earlier, (2) AP voters do not pay attention to the strength of a defeated opponent, and (3) the benefit of winning by a large margin is negligible. I conclude by noting how these results inform debates about a potential playoff in college football.
Spectral scaling and quantum critical behaviour in the pseudogap Anderson model
The pseudogap Anderson impurity model provides a classic example of an
essentially local quantum phase transition. Here we study its single-particle
dynamics in the vicinity of the symmetric quantum critical point (QCP)
separating generalized Fermi liquid and local moment phases, via the local
moment approach. Both phases are shown to be characterized by a low-energy
scale that vanishes at the QCP; and the universal scaling spectra, on all
energy scales, are obtained analytically. The spectrum precisely at the QCP is
also obtained; its form showing clearly the non-Fermi liquid, interacting
nature of the fixed point.Comment: 7 pages, 2 figure
A spin-dependent local moment approach to the Anderson impurity model
We present an extension of the local moment approach to the Anderson impurity
model with spin-dependent hybridization. By employing the two-self-energy
description, as originally proposed by Logan and co-workers, we applied the
symmetry restoration condition for the case with spin-dependent hybridization.
Self-consistent ground states were determined through variational minimization
of the ground state energy. The results obtained with our spin-dependent local
moment approach applied to a quantum dot system coupled to ferromagnetic leads
are in good agreement with those obtained from previous work using numerical
renormalization group calculations
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