One-point fluctuation analysis of IceCube neutrino events outlines a significant unassociated isotropic component and constrains the Galactic contribution

The origins of the extraterrestrial neutrinos observed in IceCube have yet to be determined. In this study we perform a one-point fluctuation analysis of the six-year high-energy starting event (HESE) shower data, with fixed non-Poissonian contributions from atmospheric, Galactic and some extragalactic components, as well as an isotropic (and weakly non-Poissonian) template. In addition to the star-forming galaxies and blazars, our analysis suggests the presence of an additional isotropic component, not associated with any known class of sources, with best-fit intensity of $(2.8\pm0.2)\times 10^{-18}\,(E/100~{\rm TeV})^{-2.7\pm 0.5}$ ${\mathrm{cm}^{-2}\, \mathrm{s}^{-1}\,\mathrm{sr}^{-1}\,\mathrm{GeV}^{-1}}$. For the first time, we also consider high-energy extrapolations of several phenomenological models for the diffuse Galactic emission (tuned to both local cosmic-ray data and diffuse gamma-ray emission in the GeV-TeV domain). We demonstrate the potential of our framework in discriminating between different scenarios, with possible implications on the physics of cosmic ray transport in the TeV-PeV range.Comment: 10 pages, 3 figures, accepted for publication in PR

Modelling the flux distribution function of the extragalactic gamma-ray background from dark matter annihilation

The one-point function (i.e., the isotropic flux distribution) is a complementary method to (anisotropic) two-point correlations in searches for a gamma-ray dark matter annihilation signature. Using analytical models of structure formation and dark matter halo properties, we compute the gamma-ray flux distribution due to annihilations in extragalactic dark matter halos, as it would be observed by the Fermi Large Area Telescope. Combining the central limit theorem and Monte Carlo sampling, we show that the flux distribution takes the form of a narrow Gaussian of `diffuse' light, with an `unresolved point source' power-law tail as a result of bright halos. We argue that this background due to dark matter constitutes an irreducible and significant background component for point-source annihilation searches with galaxy clusters and dwarf spheroidal galaxies, modifying the predicted signal-to-noise ratio. A study of astrophysical backgrounds to this signal reveals that the shape of the total gamma-ray flux distribution is very sensitive to the contribution of a dark matter component, allowing us to forecast promising one-point upper limits on the annihilation cross section. We show that by using the flux distribution at only one energy bin, one can probe the canonical cross section required for explaining the relic density, for dark matter of masses around tens of GeV.Comment: 33 pages, 10 figures; Minor changes to reflect version accepted by JCA

Interference of an Array of Independent Bose-Einstein Condensates

Interference of an array of independent Bose-Einstein condensates, whose experiment has been performed recently, is theoretically studied in detail. Even if the number of the atoms in each gas is kept finite and the phases of the gases are not well defined, interference fringes are observed on each snapshot. The statistics of the snapshot interference patterns, i.e., the average fringe amplitudes and their fluctuations (covariance), are computed analytically, and concise formulas for their asymptotic values for long time of flight are derived. Processes contributing to these quantities are clarified and the relationship with the description on the basis of the symmetry-breaking scenario is revealed.Comment: 13 pages, 3 figure

Self-Consistent Electron Subbands of Gaas/Algaas Heterostructure in Magnetic Fields Parallel to the Interface

The effect of strong magnetic fields parallel to GaAs/AlGaAs interface on the subband structure of a 2D electron layer is ivestigated theoretically. The system with two levels occupied in zero magnetic field is considered and the magnetic field induced depletion of the second subband is studied. The confining potential and the electron dispersion relations are calculated self-consistently, the electron- electron interaction is taken into account in the Hartree approximation.Comment: written in LaTeX, 8 pages, 4 figs. available on request from [email protected]

Induced spin-orbit coupling in silicon thin films by bismuth doping

We demonstrate an enhancement of the spin-orbit coupling in silicon (Si) thin films by doping with bismuth (Bi), a heavy metal, using ion implantation. Quantum corrections to conductance at low temperature in phosphorous-doped Si before and after Bi implantation is measured to probe the increase of the spin-orbit coupling, and a clear modification of magnetoconductance signals is observed: Bi doping changes magnetoconductance from weak localization to the crossover between weak localization and weak antilocalization. The elastic diffusion length, phase coherence length and spin-orbit coupling length in Si with and without Bi implantation are estimated, and the spin-orbit coupling length after the Bi doping becomes the same order of magnitude (Lso = 54 nm) with the phase coherence length (L{\phi} = 35 nm) at 2 K. This is an experimental proof that the spin-orbit coupling strength in Si thin film is tunable by doping with heavy metals.Comment: 13 pages, 3 figure

How bright can the brightest neutrino source be?

After the discovery of extraterrestrial high-energy neutrinos, the next major goal of neutrino telescopes will be identifying astrophysical objects that produce them. The flux of the brightest source $F_{\rm max}$, however, cannot be probed by studying the diffuse neutrino intensity. We aim at constraining $F_{\rm max}$ by adopting a broken power-law flux distribution, a hypothesis supported by observed properties of any generic astrophysical sources. The first estimate of $F_{\rm max}$ comes from the fact that we can only observe one universe, and hence, the expected number of sources above $F_{\rm max}$ cannot be too small compared with one. For abundant source classes such as starburst galaxies, this one-source constraint yields a value of $F_{\rm max}$ that is an order of magnitude lower than the current upper limits from point-source searches. Then we derive upper limits on $F_{\rm max}$ assuming that the angular power spectrum is consistent with neutrino shot noise yet. We find that the limits obtained with upgoing muon neutrinos in IceCube can already be quite competitive, especially for rare but bright source populations such as blazars. The limits will improve nearly quadratically with exposure, and therefore be even more powerful for the next generation of neutrino telescopes.Comment: 13 pages, 10 figures, accepted by Phys.Rev.

Abrupt transition in quasiparticle dynamics at optimal doping in a cuprate superconductor system

We report time-resolved measurements of the photoinduced change in reflectivity, Delta R, in the Bi2Sr2Ca(1-y)Dy(y)Cu2O(8+delta) (BSCCO) system of cuprate superconductors as a function of hole concentration. We find that the kinetics of quasiparticle decay and the sign of Delta R both change abruptly where the superconducting transition temperature Tc is maximal. These coincident changes suggest that a sharp transition in quasiparticle dynamics takes place precisely at optimal doping in the BSCCO system.Comment: 10 pages, 4 figure

Large magnetothermal conductivity in GdBaCo_{2}O_{5+x} single crystals

To study the effects of paramagnetic spins on phonons, both the in-plane and the c-axis heat transport of GdBaCo_{2}O_{5+x} (GBCO) single crystals are measured at low temperature down to 0.36 K and in magnetic field up to 16 T. It is found that the phonon heat transport is very strongly affected by the magnetic field and nearly 5 times increase of the thermal conductivity in several Tesla field is observed at 0.36 K. It appears that phonons are resonantly scattered by paramagnetic spins in zero field and the application of magnetic field removes such strong scattering, but the detailed mechanism is to be elucidated.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev.

Intensity distribution of scalar waves propagating in random media

Transmission of the scalar field through the random medium, represented by the system of randomly distributed dielectric cylinders is calculated numerically. System is mapped to the problem of electronic transport in disordered two-dimensional systems. Universality of the statistical distribution of transmission parameters is analyzed in the metallic and in the localized regimes.In the metallic regime the universality of the transmission statistics in all transparent channels is observed. In the band gaps, we distinguish the disorder induced (Anderson) localization from the tunneling through the system due to the gap in the density of states. We show also that absorption causes rapid decrease of the mean conductance, but, contrary to the localized regime, the conductance is self-averaged with a Gaussian distribution

Radiative neutron capture on a proton at BBN energies

The total cross section for radiative neutron capture on a proton, $np \to d \gamma$, is evaluated at big bang nucleosynthesis (BBN) energies. The electromagnetic transition amplitudes are calculated up to next-to leading order within the framework of pionless effective field theory with dibaryon fields. We also calculate the $d\gamma\to np$ cross section and the photon analyzing power for the $d\vec{\gamma}\to np$ process from the amplitudes. The values of low energy constants that appear in the amplitudes are estimated by a Markov Chain Monte Carlo analysis using the relevant low energy experimental data. Our result agrees well with those of other theoretical calculations except for the $np\to d\gamma$ cross section at some energies estimated by an R-matrix analysis. We also study the uncertainties in our estimation of the $np\to d\gamma$ cross section at relevant BBN energies and find that the estimated cross section is reliable to within $\sim$1% error.Comment: 21 pages and 12 eps figures; 6 eps figures and 2 references added, and accepted for publication in Phys. Rev.