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 $h^0$, $H^{\pm}$ 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 $\Gamma (h^0\to b \bar b)$ decay width approaches its Standard Model value at one loop, with the onset of decoupling being delayed for large $\tan\beta$ 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 $\tan\beta$, is found in the SUSY-QCD corrections to the $\Gamma (H^+\to t \bar b)$ decay width at one loop. In contrast, the SUSY-QCD corrections in the $\Gamma (t\to W^+ b)$ 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