10,818 research outputs found
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
Dynamics and transport properties of heavy fermions: theory
The paramagnetic phase of heavy fermion systems is investigated, using a
non-perturbative local moment approach to the asymmetric periodic Anderson
model within the framework of dynamical mean field theory. The natural focus is
on the strong coupling Kondo-lattice regime wherein single-particle spectra,
scattering rates, dc transport and optics are found to exhibit w/w_L,T/w_L
scaling in terms of a single underlying low-energy coherence scale w_L.
Dynamics/transport on all relevant (w,T)-scales are encompassed, from the
low-energy behaviour characteristic of the lattice coherent Fermi liquid,
through incoherent effective single-impurity physics likewise found to arise in
the universal scaling regime, to non-universal high-energy scales; and which
description in turn enables viable quantitative comparison to experiment.Comment: 27 pages, 12 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
Decoupling Properties of MSSM particles in Higgs and Top Decays
We study the supersymmetric (SUSY) QCD radiative corrections, at the one-loop
level, to , and t quark decays, in the context of the Minimal
Supersymmetric Standard Model (MSSM) and in the decoupling limit. The
decoupling behaviour of the various MSSM sectors is analyzed in some special
cases, where some or all of the SUSY mass parameters become large as compared
to the electroweak scale. We show that in the decoupling limit of both large
SUSY mass parameters and large CP-odd Higgs mass, the decay width approaches its Standard Model value at one loop, with the onset
of decoupling being delayed for large values. However, this
decoupling does not occur if just the SUSY mass parameters are taken large. A
similar interesting non-decoupling behaviour, also enhanced by , is
found in the SUSY-QCD corrections to the decay width
at one loop. In contrast, the SUSY-QCD corrections in the
decay width do decouple and this decoupling is fast.Comment: 19 pages, 10 figures. Invited talk presented by M.J.Herrero at the
5th International Symposium on Radiative Corrections (RADCOR 2000) Carmel CA,
USA, 11-15 September, 200
Determination of Higgs-boson couplings at the LHC
We investigate the determination of Higgs boson couplings to gauge bosons and
fermions at the LHC from data on Higgs boson production and decay. We
demonstrate that very mild theoretical assumptions, which are valid in general
multi-Higgs doublet models, are sufficient to allow the extraction of absolute
values of the couplings rather than just ratios of the couplings. For Higgs
masses below 200 GeV we find accuracies of 10-40% for the Higgs couplings and
the total Higgs boson width after several years of LHC running. The sensitivity
of the Higgs coupling measurements to deviations from the Standard Model
predictions is studied for an MSSM scenario.Comment: 9 pages, contribution to the proceedings of the XXXIXth Rencontres de
Moriond, La Thuile, March 200
Mortality study of 18 000 patients treated with omeprazole.
Background: The long term safety of potent gastric acid suppressive therapy has yet to be established.
Method: General practice record review at a median interval of 26 months followed by retrieval of details of all deaths within four years using the UK National Health Service Central Registers in 17 936 patients prescribed omeprazole in 1993–1995. Death rates were compared with general population rates.
Results: Records of 17 489 patients (97.5%) were examined. A total of 12 703 patients received further scripts for antisecretory drugs, 8097 for omeprazole only (65.6%): 3097 patients have died. All cause mortality was higher in the first year (observed/expected (O/E) 1.44 (95% confidence intervals (CI) 1.34–1.55); p<0.0001) but had fallen to population expectation by the fourth year. There were significant mortality increases in the first year, falling to or below population expectation by the fourth year, for deaths ascribed to neoplasms (1.82 (95% CI 1.58–2.08); p<0.0001), circulatory diseases (1.27 (95% CI 1.13–1.43); p<0.0001), and respiratory diseases (1.37 (95% CI 1.12–1.64); p<0.001). Increased mortality ascribed to digestive diseases (2.56 (95% CI 1.87–3.43); p<0.0001) persisted, although reduced. Increased mortality rates for cancers of the stomach (4.06 (95% CI 2.60–6.04); p<0.0001), colon and rectum (1.40 (95% CI 0.84–2.18); p=0.075), and trachea, bronchus, and lung (1.64 (95% CI 1.19–2.19); p<0.01) seen in the first year had disappeared by the fourth year but that for cancer of the oesophagus had not (O/E 7.35 (95% CI 5.20–10.09) (p<0.0001) in year 1; 2.88 (95% CI 1.62–4.79) (p<0.001) in year 4). Forty of 78 patients dying of oesophageal cancer had the disease present at registration. Twenty seven of those remaining cases had clinical evidence of Barrett’s disease, stricture, ulcer, or oesophagitis at registration (O/E 3.30 (95% CI 2.17–4.80)). Six deaths occurred in patients with hiatal hernia or reflux only (O/E 1.02 (95% CI 0.37–2.22)) and five in patients without oesophageal disease (O/E 0.77 (95% CI 0.25–1.80)). No relationships were detected with numbers of omeprazole scripts received.
Conclusions: Increases in mortality associated with treatment are due to pre- existing illness, including pre-existing severe oesophageal disease. There was no evidence of an increased risk of oesophageal adenocarcinoma in those without oesophageal mucosal damage recorded at registration
Variation of the cross section for e+e- --> W+H- in the Minimal Supersymmetric Standard Model
We study the loop-induced process e+e- --> W+H- in the Minimal Supersymmetric
Standard Model (MSSM). This process allows the charged Higgs boson to be
produced in e+e- collisions when its mass is larger than half the
center-of-mass energy, so that e+e- --> H+H- is kinematically forbidden. By
scanning over the MSSM parameters subject to experimental constraints we
examine the range of values possible for this cross section. We find that, in
regions of parameter space where this cross section is large enough to be of
interest, the contributions from supersymmetric particles typically increase
the cross section by 50-100% compared to the non-supersymmetric two Higgs
doublet model result. Choosing a few typical MSSM parameter sets, we show the
regions in the m_{H^{\pm}}-tan(beta) plane in which at least 10 W^{\pm}H^{\mp}
events would be produced at the e+e- collider for m_{H^{\pm}} >= sqrt(s)/2. We
also show that including radiative corrections to the MSSM Higgs sector has
only a small effect on the cross section.Comment: 5 pages, 4 figures, v2: minor changes; v3: extensive changes to text
and figures, version to appear in PR
Optical and transport properties of heavy fermions: theory compared to experiment
Employing a local moment approach to the periodic Anderson model within the
framework of dynamical mean-field theory, direct comparison is made between
theory and experiment for the dc transport and optical conductivities of
paramagnetic heavy fermion and intermediate valence metals. Four materials,
exhibiting a diverse range of behaviour in their transport/optics, are analysed
in detail: CeB6, YbAl3, CeAl3 and CeCoIn5. Good agreement between theory and
experiment is in general found, even quantitatively, and a mutually consistent
picture of transport and optics results.Comment: 21 pages, 10 figures; Replacement with minor style changes made to
avoid postscript file error
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