Some Aspects of New CDM Models and CDM Detection Methods

We briefly review some recent Cold Dark Matter (CDM) models. Our main focus are charge symmetric models of WIMPs which are not the standard SUSY LSP's (Lightest Supersymmetric Partners). We indicate which experiments are most sensitive to certain aspects of the models. In particular we discuss the manifestations of the new models in neutrino telescopes and other set-ups. We also discuss some direct detection experiments and comment on measuring the direction of recoil ions--which is correlated with the direction of the incoming WIMP. This could yield daily variations providing along with the annual modulation signatures for CDM.Comment: 14 page

Improved Gas Sensing Performance of ALD AZO 3-D Coated ZnO Nanorods

This paper reports an enhancement on the sensing performance of ZnO nanorod ethanol sensors with a new approach by utilizing nested coatings of Aluminum doped ZnO (AZO) thin films by Atomic Layer Deposition (ALD) technology. ZnO nanorods were grown by the hydrothermal method with the ZnO seed layer synthesized on Silicon wafers by ALD. To enhance the sensing performance of ZnO nanorod ethanol sensors, multiple coated AZO thin film 3-D coatings were deposited on the surface of the intrinsic ZnO nanorods by ALD.To investigate the sensing performance of the ZnO nanorods sensor for the detection of ethanol vapor, a gas sensor testing system was designed and built with a sealed reaction chamber and a temperature controller. The demonstrated sensing performance results include the sensing response comparison between ZnO nanorods before and after ALD coatings with AZO films at different temperatures and with various concentrations of input ethanol vapor. The response times and recovery times of ZnO nanorods before and after ALD coatings with AZO thin films were analyzed to investigate the sensing enhancement. The sensing response improvement peaks at 25°C room temperature with approximately 200% enhancement. However, the sensing response improvement decreases as a function of increasing operating temperature

Resummed Photon Spectra for WIMP Annihilation

We construct an effective field theory (EFT) description of the hard photon spectrum for heavy WIMP annihilation. This facilitates precision predictions relevant for line searches, and allows the incorporation of non-trivial energy resolution effects. Our framework combines techniques from non-relativistic EFTs and soft-collinear effective theory (SCET), as well as its multi-scale extensions that have been recently introduced for studying jet substructure. We find a number of interesting features, including the simultaneous presence of SCET$_{\text{I}}$ and SCET$_{\text{II}}$ modes, as well as collinear-soft modes at the electroweak scale. We derive a factorization formula that enables both the resummation of the leading large Sudakov double logarithms that appear in the perturbative spectrum, and the inclusion of Sommerfeld enhancement effects. Consistency of this factorization is demonstrated to leading logarithmic order through explicit calculation. Our final result contains both the exclusive and the inclusive limits, thereby providing a unifying description of these two previously-considered approximations. We estimate the impact on experimental sensitivity, focusing for concreteness on an SU(2)$_{W}$ triplet fermion dark matter - the pure wino - where the strongest constraints are due to a search for gamma-ray lines from the Galactic Center. We find numerically significant corrections compared to previous results, thereby highlighting the importance of accounting for the photon spectrum when interpreting data from current and future indirect detection experiments.Comment: 55+25 pages, 11+2 figures; v3, updated an expression in the appendix to make it applicable at higher order - no impact on the results in this wor

Luminescence in Slipped and Dislocation-Free Laser-Annealed Silicon

Photoluminescence of cw laser-annealed silicon shows a dramatic difference in electronic behavior of the reconstructed material depending upon either creation or suppression of dislocations. Beyond a critical exposure time slip appears, and the luminescence of these samples is dominated by dislocation-related defect levels

Optical Recording Aspects of rf Magnetron Sputtered Iron-Garnet Films

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare-earth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording. This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-Å Co and 9-Å Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y3--xBixFe5O12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor εij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240- and 248-nm wavelengths and a bismuth concentration up x=1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components ε′12 and ε″12 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x=1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co 2+- and Co3+- substituted iron garnets and barium hexaferrite BaFe12O19. Finally, the spectral dependence of the magneto-optical figure of merit 2ΘFp/α of (Y,Bi)3Fe5O12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal diffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline iron-garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for improving the film texture. Under favorable sputtering conditions single- and polycrystalline bismuth-iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence

Supersymmetric Decays of the Z' Boson

The decay of the Z' boson into supersymmetric particles is studied. We investigate how these supersymmetric modes affect the current limits from the Tevatron and project the expected sensitivities at the LHC. Employing three representative supersymmetric Z' models, namely, E_6, U(1)_{B-L}, and the sequential model, we show that the current limits of the Z' mass from the Tevatron could be reduced substantially due to the weakening of the branching ratio into leptonic pairs. The mass reach for the E_6 Z' bosons is about 1.3-1.5 TeV at the LHC-7 (1 fb^{-1}), about 2.5 - 2.6 TeV at the LHC-10 (10 fb^{-1}), and about 4.2 - 4.3 TeV at the LHC-14 (100 fb^{-1}). A similar mass reach for the U(1)_{B-L} Z' is also obtained. We also examine the potential of identifying various supersymmetric decay modes of the Z' boson because it may play a crucial role in the detailed dynamics of supersymmetry breaking.Comment: 30 pages, including 13 figures. improvements to the presentation and references adde

Forces between clustered stereocilia minimize friction in the ear on a subnanometre scale

The detection of sound begins when energy derived from acoustic stimuli deflects the hair bundles atop hair cells. As hair bundles move, the viscous friction between stereocilia and the surrounding liquid poses a fundamental challenge to the ear's high sensitivity and sharp frequency selectivity. Part of the solution to this problem lies in the active process that uses energy for frequency-selective sound amplification. Here we demonstrate that a complementary part involves the fluid-structure interaction between the liquid within the hair bundle and the stereocilia. Using force measurement on a dynamically scaled model, finite-element analysis, analytical estimation of hydrodynamic forces, stochastic simulation and high-resolution interferometric measurement of hair bundles, we characterize the origin and magnitude of the forces between individual stereocilia during small hair-bundle deflections. We find that the close apposition of stereocilia effectively immobilizes the liquid between them, which reduces the drag and suppresses the relative squeezing but not the sliding mode of stereociliary motion. The obliquely oriented tip links couple the mechanotransduction channels to this least dissipative coherent mode, whereas the elastic horizontal top connectors stabilize the structure, further reducing the drag. As measured from the distortion products associated with channel gating at physiological stimulation amplitudes of tens of nanometres, the balance of forces in a hair bundle permits a relative mode of motion between adjacent stereocilia that encompasses only a fraction of a nanometre. A combination of high-resolution experiments and detailed numerical modelling of fluid-structure interactions reveals the physical principles behind the basic structural features of hair bundles and shows quantitatively how these organelles are adapted to the needs of sensitive mechanotransduction.Comment: 21 pages, including 3 figures. For supplementary information, please see the online version of the article at http://www.nature.com/natur

Impact of RRAM Read Fluctuations on the Program-Verify Approach

The stochastic nature of the conductive filaments in oxide-based resistive memory (RRAM) represents a sizeable impediment to commercialization. As such, program-verify methodologies are highly alluring. However, it was recently shown that program-verify methods are unworkable due to strong resistance state relaxation after SET/RESET programming. In this paper, we demonstrate that resistance state relaxation is not the main culprit. Instead, it is fluctuation-induced false-reading (triggering) that defeats the program-verify method, producing a large distribution tail immediately after programming. The fluctuation impact on the verify mechanism has serious implications on the overall write/erase speed of RRAM

Analysis of two-point statistics of cosmic shear: III. Covariances of shear measures made easy

In recent years cosmic shear, the weak gravitational lensing effect by the large-scale structure of the Universe, has proven to be one of the observational pillars on which the cosmological concordance model is founded. Several cosmic shear statistics have been developed in order to analyze data from surveys. For the covariances of the prevalent second-order measures we present simple and handy formulae, valid under the assumptions of Gaussian density fluctuations and a simple survey geometry. We also formulate these results in the context of shear tomography, i.e. the inclusion of redshift information, and generalize them to arbitrary data field geometries. We define estimators for the E- and B-mode projected power spectra and show them to be unbiased in the case of Gaussianity and a simple survey geometry. From the covariance of these estimators we demonstrate how to derive covariances of arbitrary combinations of second-order cosmic shear measures. We then recalculate the power spectrum covariance for general survey geometries and examine the bias thereby introduced on the estimators for exemplary configurations. Our results for the covariances are considerably simpler than and analytically shown to be equivalent to the real-space approach presented in the first paper of this series. We find good agreement with other numerical evaluations and confirm the general properties of the covariance matrices. The studies of the specific survey configurations suggest that our simplified covariances may be employed for realistic survey geometries to good approximation.Comment: 15 pages, including 4 figures (Fig. 3 reduced in quality); minor changes, Fig. 4 extended; published in A&

Searching for the light dark gauge boson in GeV-scale experiments

We study current constraints and search prospects for a GeV scale vector boson at a range of low energy experiments. It couples to the Standard Model charged particles with a strength <= 10^-3 to 10^-4 of that of the photon. The possibility of such a particle mediating dark matter self-interactions has received much attention recently. We consider searches at low energy high luminosity colliders, meson decays, and fixed target experiments. Based on available data, searches both at colliders and in meson decays can discover or exclude such a scenario if the coupling strength is on the larger side. We emphasize that a dedicated fixed target experiment has a much better potential in searching for such a gauge boson, and outline the desired properties of such an experiment. Two different optimal designs should be implemented to cover the range of coupling strength 10^-3 to 10^-5, and < 10^-5 of the photon, respectively. We also briefly comment on other possible ways of searching for such a gauge boson.Comment: 33 pages, 5 figures; v2: corrected discussion of Upsilon decays, updates to discussion of fixed-target experiments and QED constraints, numerous minor changes, references added; v3: typo corrected relative to the JHEP published versio