Blow-up behavior of collocation solutions to Hammerstein-type volterra integral equations

We analyze the blow-up behavior of one-parameter collocation solutions for Hammerstein-type Volterra integral equations (VIEs) whose solutions may blow up in finite time. To approximate such solutions (and the corresponding blow-up time), we will introduce an adaptive stepsize strategy that guarantees the existence of collocation solutions whose blow-up behavior is the same as the one for the exact solution. Based on the local convergence of the collocation methods for VIEs, we present the convergence analysis for the numerical blow-up time. Numerical experiments illustrate the analysis

Type II superconductivity in SrPd2Ge2

Previous investigations have shown that SrPd2Ge2, a compound isostructural with "122" iron pnictides but iron- and pnictogen-free, is a conventional superconductor with a single s-wave energy gap and a strongly three-dimensional electronic structure. In this work we reveal the Abrikosov vortex lattice formed in SrPd2Ge2 when exposed to magnetic field by means of scanning tunneling microscopy and spectroscopy. Moreover, by examining the differential conductance spectra across a vortex and estimating the upper and lower critical magnetic fields by tunneling spectroscopy and local magnetization measurements, we show that SrPd2Ge2 is a strong type II superconductor with \kappa >> sqrt(2). Also, we compare the differential conductance spectra in various magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit type II superconductor in the gapless region. This way we demonstrate that the type II superconductivity is induced by the sample being in the dirty limit, while in the clean limit it would be a type I superconductor with \kappa\ << sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B 85, (2012)).Comment: 9 pages, 4 figure

Abelian Dominance in Wilson Loops

It has been conjectured that the Abelian projection of QCD is responsible for the confinement of color. Using a gauge independent definition of the Abelian projection which does {\it not} employ any gauge fixing, we provide a strong evidence for the Abelian dominance in Wilson loop integral. In specific we prove that the gauge potential which contributes to the Wilson loop integral is precisely the one restricted by the Abelian projection.Comment: 4 pages, no figure, revtex. Phys. Rev. D in pres

Color Reflection Invariance and Monopole Condensation in QCD

We review the quantum instability of the Savvidy-Nielsen-Olesen (SNO) vacuum of the one-loop effective action of SU(2) QCD, and point out a critical defect in the calculation of the functional determinant of the gluon loop in the SNO effective action. We prove that the gauge invariance, in particular the color reflection invariance, exclude the unstable tachyonic modes from the gluon loop integral. This guarantees the stability of the magnetic condensation in QCD.Comment: 28 pages, 3 figures, JHEP styl

Magnetic Moments of Heavy Baryons

First non-trivial chiral corrections to the magnetic moments of triplet (T) and sextet (S^(*)) heavy baryons are calculated using Heavy Hadron Chiral Perturbation Theory. Since magnetic moments of the T-hadrons vanish in the limit of infinite heavy quark mass (m_Q->infinity), these corrections occur at order O(1/(m_Q \Lambda_\chi^2)) for T-baryons while for S^(*)-baryons they are of order O(1/\Lambda_\chi^2). The renormalization of the chiral loops is discussed and relations among the magnetic moments of different hadrons are provided. Previous results for T-baryons are revised.Comment: 11 Latex pages, 2 figures, to be published in Phys.Rev.

Electromagnetic Decays of Heavy Baryons

The electromagnetic decays of the ground state baryon multiplets with one heavy quark are calculated using Heavy Hadron Chiral Perturbation Theory. The M1 and E2 amplitudes for S^{*}--> S gamma, S^{*} --> T gamma and S --> T gamma are separately computed. All M1 transitions are calculated up to O(1/Lambda_chi^2). The E2 amplitudes contribute at the same order for S^{*}--> S gamma, while for S^{*} --> T gamma they first appear at O(1/(m_Q \Lambda_\chi^2)) and for S --> T gamma are completely negligible. The renormalization of the chiral loops is discussed and relations among different decay amplitudes are derived. We find that chiral loops involving electromagnetic interactions of the light pseudoscalar mesons provide a sizable enhancement of these decay widths. Furthermore, we obtain an absolute prediction for the widths of Xi^{0'(*)}_c--> Xi^{0}_c gamma and Xi^{-'(*)}_b--> Xi^{-}_b gamma. Our results are compared to other estimates existing in the literature.Comment: 17 pages, 3 figures, submitted to Phys. Rev.

Evidence for nodeless superconducting gap in NaFe1−x_{1-x}Cox_xAs from low-temperature thermal conductivity measurements

The thermal conductivity of optimally doped NaFe$_{0.972}$Co$_{0.028}$As ($T_c \sim$ 20 K) and overdoped NaFe$_{0.925}$Co$_{0.075}$As ($T_c \sim$ 11 K) single crystals were measured down to 50 mK. No residual linear term $\kappa_0/T$ is found in zero magnetic field for both compounds, which is an evidence for nodeless superconducting gap. Applying field up to $H$ = 9 T ($\approx H_{c2}/4$) does not noticeably increase $\kappa_0/T$ in NaFe$_{1.972}$Co$_{0.028}$As, which is consistent with multiple isotropic gaps with similar magnitudes. The $\kappa_0/T$ of overdoped NaFe$_{1.925}$Co$_{0.075}$As shows a relatively faster field dependence, indicating the increase of the ratio between the magnitudes of different gaps, or the enhancement of gap anisotropy upon increasing doping.Comment: 5 pages, 4 figure

Conductance Correlations Near Integer Quantum Hall Transitions

In a disordered mesoscopic system, the typical spacing between the peaks and the valleys of the conductance as a function of Fermi energy $E_F$ is called the conductance energy correlation range $E_c$. Under the ergodic hypothesis, the latter is determined by the half-width of the ensemble averaged conductance correlation function: $F=$. In ordinary diffusive metals, $E_c\sim D/L^2$, where $D$ is the diffusion constant and $L$ is the linear dimension of the phase-coherent sample. However, near a quantum phase transition driven by the location of the Fermi energy $E_F$, the above picture breaks down. As an example of the latter, we study, for the first time, the conductance correlations near the integer quantum Hall transitions of which $E_F$ is a critical coupling constant. We point out that the behavior of $F$ is determined by the interplay between the static and the dynamic properties of the critical phenomena.Comment: 4 pages, 4 figures, minor corrections, to appear in Phys. Rev. Let

High-pressure effects on isotropic superconductivity in the iron-free layered pnictide superconductor BaPd2As2

While the layered 122 iron arsenide superconductors are highly anisotropic, unconventional, and exhibit several forms of electronic orders that coexist or compete with superconductivity in different regions of their phase diagrams, we find in the absence of iron in the structure that the superconducting characteristics of the end member BaPd2As2 are surprisingly conventional. Here we report on complementary measurements of specific heat, magnetic susceptibility, resistivity measurements, Andreev spectroscopy, and synchrotron high pressure x-ray diffraction measurements supplemented with theoretical calculations for BaPd2As2. Its superconducting properties are completely isotropic as demonstrated by the critical fields, which do not depend on the direction of the applied field. Under the application of high pressure, Tc is linearly suppressed, which is the typical behavior of classical phonon-mediated superconductors with some additional effect of a pressure-induced decrease in the electronic density of states and the electron-phonon coupling parameters. Structural changes in the layered BaPd2As2 have been studied by means of angle-dispersive diffraction in a diamond-anvil cell. At 12 GPa and 24.2 GPa we observed pressure induced lattice distortions manifesting as the discontinuity and, hence discontinuity in the Birch-Murnaghan equation of state. The bulk modulus is B0=40(6) GPa below 12 GPa and B0=142(3) GPa below 27.2 GPa