Impact of Dark Matter Microhalos on Signatures for Direct and Indirect Detection

Detecting dark matter as it streams through detectors on Earth relies on knowledge of its phase space density on a scale comparable to the size of our solar system. Numerical simulations predict that our Galactic halo contains an enormous hierarchy of substructures, streams and caustics, the remnants of the merging hierarchy that began with tiny Earth mass microhalos. If these bound or coherent structures persist until the present time, they could dramatically alter signatures for the detection of weakly interacting elementary particle dark matter (WIMP). Using numerical simulations that follow the coarse grained tidal disruption within the Galactic potential and fine grained heating from stellar encounters, we find that microhalos, streams and caustics have a negligible likelihood of impacting direct detection signatures implying that dark matter constraints derived using simple smooth halo models are relatively robust. We also find that many dense central cusps survive, yielding a small enhancement in the signal for indirect detection experiments.Comment: 6 pages, revision in response to referees report. Now accepted by Phys. Rev D., in pres

Fitting formulae of the reduced-shear power spectrum for weak lensing

Context. Weak gravitational lensing is a powerful probe of large-scale structure and cosmology. Most commonly, second-order correlations of observed galaxy ellipticities are expressed as a projection of the matter power spectrum, corresponding to the lowest-order approximation between the projected and 3d power spectrum. Aims. The dominant lensing-only contribution beyond the zero-order approximation is the reduced shear, which takes into account not only lensing-induced distortions but also isotropic magnification of galaxy images. This involves an integral over the matter bispectrum. We provide a fast and general way to calculate this correction term. Methods. Using a model for the matter bispectrum, we fit elementary functions to the reduced-shear contribution and its derivatives with respect to cosmological parameters. The dependence on cosmology is encompassed in a Taylor-expansion around a fiducial model. Results. Within a region in parameter space comprising the WMAP7 68% error ellipsoid, the total reduced-shear power spectrum (shear plus fitted reduced-shear correction) is accurate to 1% (2%) for l<10^4 (l<2x10^5). This corresponds to a factor of four reduction of the bias compared to the case where no correction is used. This precision is necessary to match the accuracy of current non-linear power spectrum predictions from numerical simulations.Comment: 7 pages, 3 figures. A&A in press. Revised version with minor change

Weak lensing observations of the "dark" cluster MG2016+112

We investigate the possible existence of a high-redshift (z=1) cluster of galaxies associated with the QSO lens system MG2016+112. From an ultra-deep R- and less deep V- and I-band Keck images and a K-band mosaic from UKIRT, we detect ten galaxies with colors consistent with the lensing galaxy within 225h^{-1} kpc of the z=1.01 lensing galaxy. This represents an overdensity of more than ten times the number density of galaxies with similar colors in the rest of the image. We also find a group of seven much fainter objects closely packed in a group only 27h^{-1} kpc north-west of the lensing galaxy. We perform a weak lensing analysis on faint galaxies in the R-band image and detect a mass peak of a size similar to the mass inferred from X-ray observations of the field, but located 64" northwest of the lensing galaxy. From the weak lensing data we rule out a similar sized mass peak centered on the lensing galaxy at the 2 sigma level.Comment: 9 pages, 10 figures, submitted to A&A version with figure 4 at higher resolution can be downloaded from http://www.mpa-garching.mpg.de/~clowe/mg2016aa.ps.g

High power diode laser surface glazing of concrete

This present work describes the utilisation of the relatively novel high power diode laser (HPDL) to generate a surface glaze on the ordinary Portland cement (OPC) surface of concrete. The value of such an investigation would be to facilitate the hitherto impossible task of generating a durable and long-lasting surface seal on the concrete, thereby extending the life and applications base of the concrete. The basic process phenomena are investigated and the laser effects in terms of glaze morphology, composition and microstructure are presented. Also, the resultant heat affects are analysed and described, as well as the effects of the shield gases, O2 and Ar, during laser processing. HPDL glazing of OPC was successfully demonstrated with power densities as low as 750 W cm-2 and at scanning rates up to 480 mm min-1. The work showed that the generation of the surface glaze resulted in improved mechanical and chemical properties over the untreated OPC surface of concrete. Both untreated and HPDL glazed OPC were tested for pull-off strength, rupture strength, water absorption, wear resistance and corrosion resistance. The OPC laser glaze exhibited clear improvements in wear, water sorptivity, and resistance (up to 80% concentration) to nitric acid, sodium hydroxide and detergent. Life assessment testing revealed that the OPC laser glaze had an increase in actual wear life of 1.3 to 14.8 times over the untreated OPC surface of concrete, depending upon the corrosive environment

Removable Matter-Power-Spectrum Covariance from Bias Fluctuations

We find a simple, accurate model for the covariance matrix of the real-space cosmological matter power spectrum on slightly nonlinear scales (k~0.1-0.8 h/Mpc at z=0), where off-diagonal matrix elements become substantial. The model includes a multiplicative, scale-independent modulation of the power spectrum. It has only one parameter, the variance (among realizations) of the variance of the nonlinear density field in cells, with little dependence on the cell size between 2-8 Mpc/h. Furthermore, we find that this extra covariance can be modeled out by instead measuring the power spectrum of (delta/sigma_cell), i.e. the ratio of the overdensity to its dispersion in cells a few Mpc in size. Dividing delta by sigma_cell essentially removes the non-Gaussian part of the covariance matrix, nearly diagonalizing it.Comment: Accepted to ApJ. 5 pages, 5 figures; slight clarifications to match accepted versio