Three-band superconductivity and the order parameter that breaks time-reversal symmetry

We consider a model of multiband superconductivity, inspired by iron pnictides, in which three bands are connected via repulsive pair-scattering terms. Generically, three distinct superconducting states arise within such a model. Two of them are straightforward generalizations of the two-gap order parameter while the third one corresponds to a time-reversal symmetry breaking order parameter, altogether absent within the two-band model. Potential observation of such a genuinely frustrated state would be a particularly vivid manifestation of the repulsive interactions being at the root of iron-based high temperature superconductivity. We construct the phase diagram of this model and discuss its relevance to the iron pnictides family of high temperature superconductors. We also study the case of the Josephson coupling between a two-band s' (or extended s-wave) superconductor and a single-gap s-wave superconductor, and the associated phase diagram.Comment: 9 pages, 9 figures. Added discussion and references, one new figure (Fig. 3

A Criterion for the Critical Number of Fermions and Chiral Symmetry Breaking in Anisotropic QED(2+1)

By analyzing the strength of a photon-fermion coupling using basic scattering processes we calculate the effect of a velocity anisotropy on the critical number of fermions at which mass is dynamically generated in planar QED. This gives a quantitative criterion which can be used to locate a quantum critical point at which fermions are gapped and confined out of the physical spectrum in a phase diagram of various condensed matter systems. We also discuss the mechanism of relativity restoration within the symmetric, quantum-critical phase of the theory.Comment: To appear in Physical Review

Modelling the impact of atmospheric and terrestrial inputs on the Black Sea coastal dynamics

International audienceThe dynamics on the North Western Shelf area of the Black Sea are examined, with an emphasis on the circulation induced by buoyancy due to the land drained fresh waters and by the interaction with the atmosphere, notably wind stress. A three-dimensional, multi-layer hydrodynamic model is employed with realistic topography and parameterisation of river plume physics. We focus on the seasonal patterns of transport of the river induced low-salinity waters within the Coastal Low Salinity Band and the conditions that influence their removal toward the shelf interior. The numerical simulations show that coastal circulation is greatly influenced by river runoff and especially in the case of the Danube, which is excessively high with monthly aver-aged values ranging from 5000 to 10000 m3 /s. A significant contribution of runoff comes from the neighbouring rivers. At the same time, the North Western Shelf is quite broad, so that the coastal dynamics are largely sheltered from the conditions in the deeper sea. Buoyancy due to river runoff thus dominates, creating a southward coastal current that is the predominant pathway for the land-drained inputs. As in all shelf areas, wind stress is a major circulation forcing mechanism and it modifies the buoyancy induced flow. It is shown that the seasonal variability in river runoff and wind stress, in combination with the shelf topography, determines the different pathways for the terrestrial inputs. Implications on the overall basin circulation are drawn, as the availability of low-salinity waters of river origin affects the upper Black Sea layer. Consequently, the formation of distinct water masses (such as the Cold Intermediate Layer) and the properties of the outflow toward the Mediterranean are also influenced

On the shape of the UHE cosmic ray spectrum

We fit the ultra high energy cosmic ray spectra above 10$^{19}$ eV with different injection spectra at cosmic ray sources that are uniformly and homogeneously distributed in the Universe. We conclude that the current UHE spectra are consistent with power laws of index $\alpha$ between 2.4 and 2.7. There is a slow dependence of these indices on the cosmological evolution of the cosmic ray sources, which in this model determines the end of the galactic cosmic rays spectrum.Comment: 5 pages, version accepted in PR

Neutrinos: the Key to UHE Cosmic Rays

Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely determine both the injection spectrum and the evolution model for UHECR sources - primarily because interactions during propagation obscure the early Universe from direct observation. Detection of neutrinos produced in those same interactions, coupled with UHECR results, would provide a full description of UHECR source properties.Comment: three pages, three figures. corrected typo

Active Galactic Nuclei with Starbursts: Sources for Ultra High Energy Cosmic Rays

Ultra high energy cosmic ray events presently show a spectrum, which we interpret here as galactic cosmic rays due to a starburst in the radio galaxy Cen A pushed up in energy by the shock of a relativistic jet. The knee feature and the particles with energy immediately higher in galactic cosmic rays then turn into the bulk of ultra high energy cosmic rays. This entails that all ultra high energy cosmic rays are heavy nuclei. This picture is viable if the majority of the observed ultra high energy events come from the radio galaxy Cen A, and are scattered by intergalactic magnetic fields across most of the sky.Comment: 4 pages, 1 figure, proceedings of "High-Energy Gamma-rays and Neutrinos from Extra-Galactic Sources", Heidelber

High Energy Neutrinos: Sources and Fluxes

We discuss briefly the potential sources of high energy astrophysical neutrinos and show estimates of the neutrino fluxes that they can produce. A special attention is paid to the connection between the highest energy cosmic rays and astrophysical neutrinos.Comment: 7 pages, 2 figures, submitted to the Proceedings of TAUP 2005 workshop, corrected left panel of figure

Proximity fingerprint of s+- superconductivity

We suggest a straightforward and unambiguous test to identify possible opposite signs of superconducting order parameter in different bands proposed for iron-based superconductors (s+- state). We consider proximity effect in a weakly coupled sandwich composed of a s+- superconductor and thin layer of s-wave superconductor. In such system the s-wave order parameter is coupled differently with different s+- gaps and it typically aligns with one of these gaps. This forces the other s+- gap to be anti-aligned with the s-wave gap. In such situation the aligned band induces a peak in the s-wave density of states (DoS), while the anti-aligned band induces a dip. Observation of such contact-induced negative feature in the s-wave DoS would provide a definite proof for s+- superconductivity.Comment: 4 pages, one figur

Charged Higgs boson contribution to ντN→τ−X\nu_{\tau} {\cal N} \to \tau^- X for very large tan⁡β\tan\beta in the two Higgs doublet model with UHE-neutrinos

We study the deep inelastic process $\nu_{\tau} + {\cal N} \to \tau^{-} + X$ (with ${\cal N} \equiv (n+p)/2$ an isoscalar nucleon), in the context of the two Higgs doublet model {\it type two} (2HDM(II)). In particular, we discuss the contribution to the total cross section of diagrams, in which a charged Higgs boson is exchanged. We show that for large values of $\tan\beta$ such contribution for an inclusive dispersion generated through the collision of an ultrahigh energy tau-neutrino on a target nucleon can reach up to 57% of the value of the contribution of the $W^+$ exchange diagrams (i.e. can reach up to 57% of the standard model (SM) prediction) and could permit to distinguish between the SM and the 2HDM(II) predictions at the Pierre Auger Observatory.Comment: 10 pages, 5 figure