Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality

We study lattice effects in strongly coupled systems of fermions at a finite density described by a holographic dual consisting of fermions in Anti-de-Sitter space in the presence of a Reissner-Nordstrom black hole. The lattice effect is encoded by a periodic modulation of the chemical potential with a wavelength of order of the intrinsic length scales of the system. This corresponds with a highly complicated "band structure" problem in AdS, which we only manage to solve in the weak potential limit. The "domain wall" fermions in AdS encoding for the Fermi surfaces in the boundary field theory diffract as usually against the periodic lattice, giving rise to band gaps. However, the deep infrared of the field theory as encoded by the near horizon AdS2 geometry in the bulk reacts in a surprising way to the weak potential. The hybridization of the fermions bulk dualizes into a linear combination of CFT1 "local quantum critical" propagators in the bulk, characterized by momentum dependent exponents displaced by lattice Umklapp vectors. This has the consequence that the metals showing quasi-Fermi surfaces cannot be localized in band insulators. In the AdS2 metal regime, where the conformal dimension of the fermionic operator is large and no Fermi surfaces are present at low T/\mu, the lattice gives rise to a characteristic dependence of the energy scaling as a function of momentum. We predict crossovers from a high energy standard momentum AdS2 scaling to a low energy regime where exponents found associated with momenta "backscattered" to a lower Brillioun zone in the extended zone scheme. We comment on how these findings can be used as a unique fingerprint for the detection of AdS2 like "pseudogap metals" in the laboratory.Comment: 42 pages, 5 figures; v2, minor correction, to appear in JHE

Spectral function of the supersymmetry current

We continue our study of the retarded Green's function of the universal fermionic supersymmetry current ("supercurrent") for the most general class of d=3 N=2 SCFTs with D=10 or D=11 supergravity duals by studying the propagation of the Dirac gravitino in the electrically charged AdS-Reissner-Nordstr\"om black-brane background of N=2 minimal gauged supergravity in D=4. We expand upon results presented in a companion paper, including the absence of a Fermi surface and the appearance of a soft power-law gap at zero temperature. We also present the analytic solution of the gravitino equation in the AdS_2 X R^2 background which arises as the near-horizon limit at zero temperature. In addition we determine the quasinormal mode spectrum.Comment: 65 pages, 6 Figs; version published in journa

Endocarditis in the elderly: clinical, echocardiographic, and prognostic features

Aims Infective endocarditis (IE) is more and more frequent in elderly persons and it has been associated with various clinical, bacteriological, and prognostic features. The aim of the study was to define the clinical, echographic, and prognostic characteristics of IE in a large population of elderly patients from four European centres (three French, one Italian). Methods and results Three hundred and fifteen consecutive patients with definite IE underwent clinical evaluation, echocardiography, blood cultures, and follow-up. Patients were separated into three groups: group A: 117 patients aged <50 years, group B: 111 patients aged >50 and 70 years. Elderly patients (group C) presented more frequently than other groups with digestive or urinary portal of entry, pacemaker endocarditis, and anaemia. S bovis endocarditis was less frequent and S aureus endocarditis more frequent in younger (group A) patients than in other groups. No difference was observed among groups concerning echocardiographic data as well as the incidence and localization of embolic events. Elderly patients were operated on as frequently as younger patients and their operative risk was similar than in other groups (11%, 3%, and 5% in groups C, B, and A, respectively, P=ns). Overall mortality in elderly patients was low (17%) but significantly higher than in younger patients (10% in group A, 7% in group B, P=0.02). By multivariate analysis, the only risk factors for in-hospital mortality were age (P=0.003), prosthetic valve (P=0.002), and cerebral embolism (P=0.006). Conversely, surgical management was associated with a lower in hospital mortality (P=0.03). Conclusions In this largest series of elderly patients with IE, IE in elderly carries specific features when compared with younger patients, although the echographic characteristics and embolic risk are similar. The overall mortality rate in elderly patients is higher than in younger, but the mortality in operated patients is low and similar than that of younger patient