Dynamics of the Gribov horizon: A one-mode treatment

Properties of the Gribov horizon in Coulomb-gauge nonabelian Yang-Mills theory are studied in an approximation which retains global color symmetry but truncates the spin-space degrees of freedom of the transverse gauge field to a single mode. The facilities an explicit evaluation of the contribution of the Faddeev-Popov zeroes to the effective quantum potential, which is accomplished with a sturmian expansion in the zero modes of the inverse ghost propagator. In particular, the singularities of the one-mode hamiltonian at the horizon are isolated and analyzed for their effect on the spectrum. Quantizing on the compact manifold S³ and utilizing the hyperspherical techniques developed by Cutkosky, the formalism is applied to pure gluonic systems of long-wave-length modes. It is found that in the limit a cutoff on integration over ghost momenta is removed to infinity, the hamiltonian reduces to a trivial (quadratic) theory with a mass gap which is a simple multiplicative modification of the free-field result.     

Effect of harmonic confinement on correlation studies of a spin-polarized s-wave superconductor

We study different correlation functions for a spin imbalanced and harmonically trapped Fermi gas in two dimensions described by an attractive Hubbard model. Eigensolutions obtained via numerically solving Bogoliubov de Gennes equations are used to compute the local pairing amplitudes which show significantly different behaviour for the trapped case where the profile is radially modulated in contrast with a spatial modulation extending throughout the lattice geometry when trap effects are switched off. Further, different experimentally accessible quantities, such as pair–pair, density–density correlations and local density fluctuations show characteristic fluctuations for the spin polarized phase, which however wash away as the trapping effects are turned on. A contrasting scenario is presented corresponding to the case when the spin polarization effects are turned off.     

On projection (in)dependence of the dual superconductor mechanism of confinement

We study the temperature dependence of the monopole condensate in different Abelian projections of the SU(2) gauge theory on the lattice. Using the Fröhlich-Marchetti monopole creation operator, we show numerically that the monopole condensate depends on the choice of the Abelian projection.     

Strong-coupling study of the Gribov ambiguity in lattice Landau gauge

We study the strong-coupling limit β=0 of lattice SU(2) Landau gauge Yang–Mills theory. In this limit the lattice spacing is infinite, and thus all momenta in physical units are infinitesimally small. Hence, the infrared behavior can be assessed at sufficiently large lattice momenta. Our results show that at the lattice volumes used here, the Gribov ambiguity has an enormous effect on the ghost propagator in all dimensions. This underlines the severity of the Gribov problem and calls for refined studies also at finite β. In turn, the gluon propagator only mildly depends on the Gribov ambiguity.     

A modification of Faddeev-Popov approach free from Gribov ambiguity

We propose a modified version of the Faddeev-Popov (FP) quantization approach for non-Abelian gauge field theory to avoid Gribov ambiguity. We show that by means of introducing a new method of inserting the correct identity into the Yang-Mills generating functional and considering the identity generated by an integral through a subgroup of the gauge group, the problem of Gribov ambiguity can be removed naturally. Meanwhile by handling the absolute value of the FP determinant with the method introduced by Williams and collaborators, we lift the Jacobian determinant together with the absolute value and obtain a local Lagrangian. The new Lagrangian will have a nilpotent symmetry which can be viewed as an analog of the Becchi-Rouet-Stora-Tyutin symmetry.     

Photoemission study of iron-based superconductor

The iron-based superconductivity (IBSC) is a great challenge in correlated system. Angle-resolved photoemission spectroscopy (ARPES) provides electronic structure of the IBSCs, the pairing strength, and the order parameter symmetry. Here, we briefly review the recent progress in IBSCs and focus on the results from ARPES. The ARPES study shows the electronic structure of 122, 111, 11, and 122 families of IBSCs. It has been agreed that the IBSCs are unconventional superconductors in strong coupling region. The order parameter symmetry basically follows s ± form with considerable out-of-plane contribution.     

CaPtAs: A new noncentrosymmetric superconductor

We report the discovery of a new noncentrosymmetric superconductor CaPtAs.It crystallizes in a tetragonal structure(space group I41md,No.109),featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis(a=b=4.18?,and c=43.70?).The superconductivity of CaPtAs with Tc=1.47 K was characterized by means of electrical resistivity,specific heat,and ac magnetic susceptibility.The electronic specific heat Ce(T)/T shows evidence for a deviation from the behavior of a conventional BCS superconductor,and can be reasonably fitted by a p-wave model.The upper critical fieldμ0Hc2 of CaPtAs exhibits a moderate anisotropy,with an in-plane value of around 204 mT and an out-of-plane value of 148 mT.Density functional theory calculations indicate that the Pt-5 d and As-4 p orbitals mainly contribute to the density of states near the Fermi level,showing that the Pt-As honeycomb networks may significantly influence the superconducting properties.     

Parton confinement: A different perspective

Partons (quarks) are unobservable, it is suggested, because they have no well-defined rest-massconcept.     

A study of detonation propagation and diffraction with compliant confinement

Previous computational studies of diffracting detonations with the ignition-and-growth (IG) model demonstrated that, contrary to experimental observations, the computed solution did not exhibit dead zones. For a rigidly confined explosive it was found that while diffraction past a sharp corner did lead to a temporary separation of the lead shock from the reaction zone, the detonation re-established itself in due course and no pockets of unreacted material remained. The present investigation continues to focus on the potential for detonation failure within the IG model, but now for a compliant confinement of the explosive. The aim of the present paper is two-fold. First, in order to compute solutions of the governing equations for multi-material reactive flow, a numerical method is developed and discussed. The method is a Godunov-type, fractional-step scheme which incorporates an energy correction to suppress numerical oscillations that occur near material interfaces for standard conservative schemes. The accuracy of the solution method is then tested using a two-dimensional rate-stick problem for both strong and weak confinements. The second aim of the paper is to extend the previous computational study of the IG model by considering two related problems. In the first problem, the corner-turning configuration is re-examined, and it is shown that in the matter of detonation failure, the absence of rigid confinement does not affect the outcome in a material way; sustained dead zones continue to elude the model. In the second problem, detonations propagating down a compliantly confined pencil-shaped configuration are computed for a variety of cone angles of the tapered section. It is found, in accord with experimental observation, that if the cone angle is small enough, the detonation fails prior to reaching the cone tip. For both the corner-turning and the pencil-shaped configurations, mechanisms underlying the behaviour of the computed solutions are identified.     

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48 nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450 °C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe₂O₃. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.     

Quark-lepton compositeness: A three-body scenario

The Harari-Shupe model of quarks and leptons is viewed, not as a gauge theory, but as a quantum-mechanical three-body problem of the extreme relativistic type involving massless preons. Considerations based onS ₃-symmetry in the available degrees of freedom (spin, isospin, space and hypercolour) are employed in conjunction with a spin-dependence ansatz on the three-preon forces (Σ ^a =σ _μv ⁽¹⁾ σ _λμ ⁽³⁾ ) for an understanding of the three basic issues of (i) spin-1/2, (ii) generation structure and (iii) steeply rising mass patterns of quark-lepton families. The Σ ^a -dynamics is compatible with the interpretation of colour as a manifestation ofS ₃-symmetry, as envisaged in the original Harari-Shupe proposal, while the interpretation of the generation structure devolves on the role of a certain quantum numberN which takes on three different classes of values (3n, 3n ± 1;n = 0, 1, 2, ...) according to theS ₃-symmetry of thespatial wavefunction.     

A new approach to studying local gravitomagnetic effects on a superconductor

In this paper we introduce gravitomagnetic field equations into the investigation of gravitomagnetic effects on a superconductor. We point out that in the absence of an applied magnetic field, an applied gravitomagnetic field will induce twin currents, gravitational and electric supercurrents. The latter will create a magnetic field. The slightly modified Josephson, London, and London-type gravitomagnetic equations are obtained. Some applications of these equations are discussed.     

NMR study of Chevrel phase superconductor

The nuclear spin lattice relaxation time, T₁, the Knight shift and the spin echo decay time, T₂, of ²⁰⁷Pb and ⁷⁷Se were measured in Pb_1.125Mo₆Se_7.5 and Pb_1.125Mo₆S_7.5 at He temperatures. The temperature dependence of T₁ shows the existence of the energy gap of 3.5kT_c at both sites of Pb and Se. The Knight shift dose not change with temperature even below T_c. A remarkable decrease of T₂ below T_c is observed, which is opposite to the case in usual type II superconductor.     

Raman spectrum of Si nanowires: temperature and phonon confinement effects

The Raman spectrum of Si nanowires (NWs) is a matter of controversy. Usually, the one-phonon band appears broadened and shifted. This behaviour is interpreted in terms of phonon confinement; however, similar effects are observed for NWs with dimensions for which phonon confinement does not play any relevant role. In this context, the temperature increase induced by the laser beam is recognized to play a capital role in the shape of the spectrum. The analysis of the Raman spectrum, under the influence of the heating induced by the laser beam, is strongly dependent on the excitation conditions and the properties of the NWs. We present herein an analysis of the Raman spectrum of Si NWs based on a study of the interaction between the laser beam and the NWs, for both ensembles of NWs and individual NWs, taking account of the temperature increase in the NWs under the focused laser beam and the dimensions of the NWs.     

Direct observation of nonlocal effects in a superconductor

We have used the technique of low energy muon spin rotation to measure the local magnetic field profile B(z) beneath the surface of a lead film maintained in the Meissner state (z depth from the surface, z less, similar 200 nm). The data unambiguously show that B(z) clearly deviates from an exponential law and represent the first direct, model independent proof for a nonlocal response in a superconductor.