3,908 research outputs found
Symmetric Skyrmions
We present candidates for the global minimum energy solitons of charge one to
nine in the Skyrme model, generated using sophisticated numerical algorithms.
Assuming the Skyrme model accurately represents the low energy limit of QCD,
these configurations correspond to the classical nuclear ground states of the
light elements. The solitons found are particularly symmetric, for example, the
charge seven skyrmion has icosahedral symmetry, and the shapes are shown to fit
a remarkable sequence defined by a geometric energy minimization (GEM) rule. We
also calculate the energies and sizes to within at least a few percent
accuracy. These calculations provide the basis for a future investigation of
the low energy vibrational modes of skyrmions and hence the possibility of
testing the Skyrme model against experiment.Comment: latex, 9 pages, 1 figure (fig1.gif
Theory of many-fermion systems II: The case of Coulomb interactions
In a recent paper (cond-mat/9703164) a general field-theoretical description
of many-fermion systems with short-ranged interactions has been developed. Here
we extend this theory to the case of disordered electrons interacting via a
Coulomb potential. A detailed discussion is given of the Ward identity that
controls the soft modes in the system, and the generalized nonlinear sigma
model for the Coulombic case is derived and discussed.Comment: 12 pp., REVTeX, no figs, final version as publishe
Exact Nonperturbative Unitary Amplitudes for 1->N Transitions
I present an extension to arbitrary N of a previously proposed field
theoretic model, in which unitary amplitudes for processes were
obtained. The Born amplitude in this extension has the behavior
expected in a bosonic field theory. Unitarity
is violated when , or when Numerical
solutions of the coupled Schr\"odinger equations shows that for weak coupling
and a large range of N>\ncrit, the exact unitary amplitude is reasonably fit
by a factorized expression |A(1->N)| \sim (0.73 /N) \cdot \exp{(-0.025/\g2)}.
The very small size of the coefficient 1/\g2 , indicative of a very weak
exponential suppression, is not in accord with standard discussions based on
saddle point analysis, which give a coefficient The weak dependence
on could have experimental implications in theories where the exponential
suppression is weak (as in this model). Non-perturbative contributions to
few-point correlation functions in this theory would arise at order $K\ \simeq\
\left((0.05/\g2)+ 2\ ln{N}\right)/ \ ln{(1/\g2)}\g2.$Comment: 11 pages, 3 figures (not included
Correlation functions of higher-dimensional Luttinger liquids
Using higher-dimensional bosonization, we study correlation functions of
fermions with singular forward scattering. Following Bares and Wen [Phys. Rev.
B 48, 8636 (1993)], we consider density-density interactions in d dimensions
that diverge for small momentum transfers as q^{- eta} with eta = 2 (d-1). In
this case the single-particle Green's function shows Luttinger liquid behavior.
We discuss the momentum distribution and the density of states and show that,
in contrast to d=1, in higher dimensions the scaling behavior cannot be
characterized by a single anomalous exponent. We also calculate the irreducible
polarization for q close to 2 k_F and show that the leading singularities
cancel. We discuss consequences for the effect of disorder on
higher-dimensional Luttinger liquids.Comment: 7 RevTex pages, 2 figures, minor modifications, to appear in Phys.
Rev. B (Feb. 1999
Quasiparticle thermal conductivity in the vortex state of high-T cuprates
We present the results of a microscopic calculation of the longitudinal
thermal conductivity, , of a d-wave superconductor in the mixed state.
Our results show an increase in the thermal conductivity with the applied field
at low temperatures, and a decrease followed by a nearly field independent
at higher temperatures, in qualitative agreement with the
experimental results. We discuss the relationship between the slope of the
superconducting gap and the plateau in .Comment: 4 pages, 3 figures, very minor changes to text, published versio
Association of psychological distress, quality of life and costs with carpal tunnel syndrome severity: a crosssectional analysis of the PALMS cohort
Objectives:
The PALMS study is designed to identify prognostic factors for outcome from corticosteroid injection and surgical decompression for carpal tunnel syndrome (CTS) and predictors of cost over 2 years. The aim of this paper is to explore the cross-sectional association of baseline patient-reported and clinical severity with anxiety, depression, health-related quality of life and costs of CTS in patients referred to secondary care.
Methods:
Prospective, multi-centre cohort study initiated in 2013. We collected baseline data on patientreported symptom severity (CTS-6), psychological status (HADS), hand function (Michigan Hand Questionnaire) comorbidities, EQ5D-3L and sociodemographic variables. Nerve conduction tests classified patients into five severity grades (mild to very severe). Data were analysed using a general linear model.
Results:
753 patients with CTS provided complete baseline data. Multivariable linear regression adjusting for age, sex, ethnicity, duration of CTS, smoking status, alcohol consumption, employment status, body mass index and comorbidities showed a highly statistically significant relationship between CTS-6 and anxiety, depression and the EQ-5D (p<0.0001 in each case). Likewise, a significant relationship was observed between electrodiagnostic severity and anxiety (p=0.027) but not with depression (p=0.986) or the EQ-5D (p=0.257). NHS and societal costs in the 3 months prior to enrolment were significantly associated with self-reported severity (p<0.0001) but not with electrodiagnostic severity.
Conclusions:
Patient-reported symptom severity in carpal tunnel syndrome is significantly and positively associated with anxiety, depression, health-related quality of life and NHS and societal costs even when adjusting for age, gender, body mass index, comorbidities, smoking, drinking and occupational status. In contrast there is little or no evidence of any relationship with objectively derived CTS severity. Future research is needed to understand the impact of approaches and treatments that
address psychosocial stressors as well as biomedical factors on relief of symptoms from carpal tunnel syndrome.CJH was funded by the National Institute for Health Research (NIHR) through a NIHR Senior Research Fellowship. ECFW is funded by the NIHR Cambridge Biomedical Research Centre
Theory of Fermion Liquids
We develop a general theory of fermion liquids in spatial dimensions greater
than one. The principal method, bosonization, is applied to the cases of short
and long range longitudinal interactions, and to transverse gauge interactions.
All the correlation functions of the system may be obtained with the use of a
generating functional. Short-range and Coulomb interactions do not destroy the
Landau Fermi fixed point. Novel fixed points are found, however, in the cases
of a super-long range longitudinal interaction in two dimensions and transverse
gauge interactions in two and three spatial dimensions. We consider in some
detail the 2+1-dimensional problem of a Chern-Simons gauge action combined with
a longitudinal two-body interaction which
controls the density, and hence gauge, fluctuations. For we find that
the gauge interaction is irrelevant and the Landau fixed point is stable, while
for the interaction is relevant and the fixed point cannot be accessed
by bosonization. Of special importance is the case (Coulomb
interaction) which describes the Halperin-Lee-Read theory of the half-filled
Landau level. We obtain the full quasiparticle propagator which is of a
marginal Fermi liquid form. Using Ward Identities, we show that neither the
inclusion of nonlinear terms in the fermion dispersion, nor vertex corrections,
alters our results: the fixed point is accessible by bosonization. As the
two-point fermion Green's function is not gauge invariant, we also investigate
the gauge-invariant density response function. Near momentum , in
addition to the Kohn anomaly we find singular behavior. In Appendices we
present a numerical calculation of the spectral function for a Fermi liquid
with Landau parameter . We also show how Kohn's theorem isComment: Minor corrections and clarifications, and additional references. 30
pages, RevTex 3.0, 3 figures in uuencoded postscript files
Magnetoresistance of composite fermions at \nu=1/2
We have studied temperature dependence of both diagonal and Hall resistivity
in the vicinity of . Magnetoresistance was found to be positive and
almost independent of temperature: temperature enters resistivity as a
logarithmic correction. At the same time, no measurable corrections to the Hall
resistivity has been found. Neither of these results can be explained within
the mean-field theory of composite fermions by an analogy with conventional
low-field interaction theory. There is an indication that interactions of
composite fermions with fluctuations of the gauge field may reconcile the
theory and experiment.Comment: 9 pages, 4 figure
Inversion symmetric 3-monopoles and the Atiyah-Hitchin manifold
We consider 3-monopoles symmetric under inversion symmetry. We show that the
moduli space of these monopoles is an Atiyah-Hitchin submanifold of the
3-monopole moduli space. This allows what is known about 2-monopole dynamics to
be translated into results about the dynamics of 3-monopoles. Using a numerical
ADHMN construction we compute the monopole energy density at various points on
two interesting geodesics. The first is a geodesic over the two-dimensional
rounded cone submanifold corresponding to right angle scattering and the second
is a closed geodesic for three orbiting monopoles.Comment: latex, 22 pages, 2 figures. To appear in Nonlinearit
Non-Relativistic Fermions Coupled to Transverse Gauge-Fields: The Single-Particle Green's Function in Arbitrary Dimension
We use a bosonization approach to calculate the single-particle Green's
function of non-relativistic fermions coupled to
transverse gauge-fields in arbitrary dimension . We find that in
transverse gauge-fields do not destroy the Fermi liquid, although for
the quasi-particle damping is anomalously large. For the
quasi-particle residue vanishes as
, where
is the Thomas-Fermi wave-vector, is the mass of the electrons, and
is the velocity of the gauge-particle. In the system is a Luttinger
liquid, with anomalous dimension
. For we
find that decays exponentially at large distances.Comment: RevTex, no figures
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