Probing light WIMPs with directional detection experiments

The CoGeNT and CRESST WIMP direct detection experiments have recently observed excesses of nuclear recoil events, while the DAMA/LIBRA experiment has a long standing annual modulation signal. It has been suggested that these excesses may be due to light mass, m_chi ~ 5-10 GeV, WIMPs. The Earth's motion with respect to the Galactic rest frame leads to a directional dependence in the WIMP scattering rate, providing a powerful signal of the Galactic origin of any recoil excess. We investigate whether direct detection experiments with directional sensitivity have the potential to observe this anisotropic scattering rate with the elastically scattering light WIMPs proposed to explain the observed excesses. We find that the number of recoils required to detect an anisotropic signal from light WIMPs at 5 sigma significance varies from 7 to more than 190 over the set of target nuclei and energy thresholds expected for directional detectors. Smaller numbers arise from configurations where the detector is only sensitive to recoils from the highest speed, and hence most anisotropic, WIMPs. However, the event rate above threshold is very small in these cases, leading to the need for large experimental exposures to accumulate even a small number of events. To account for this sensitivity to the tail of the WIMP velocity distribution, whose shape is not well known, we consider two exemplar halo models spanning the range of possibilities. We also note that for an accurate calculation the Earth's orbital speed must be averaged over. We find that the exposures required to detect 10 GeV WIMPs at a WIMP-proton cross-section of 10^-4 pb are of order 10^3 kg day for a 20 keV energy threshold, within reach of planned directional detectors. Lower WIMP masses require higher exposures and/or lower energy thresholds for detection.Comment: 9 pages, 6 figures, v2: version to appear in Phys. Rev. D with additional discussio

Who goes to a sexual health clinic? Gender differences in service utilisation.

Aim: Our aim was to review utilisation of the Hamilton Sexual Health Clinic (Hamilton, Waikato, New Zealand) with regard to gender differences. Methods: Notes of those attending during 9 months (1 February 2008–31 October 2008) were reviewed—and their demographic details, source of referral, reasons for attending, and diagnostic coding data were compared. In addition, Waikato Hospital laboratory provided Chlamydia trachomatis test results for the study period. Data was analysed for gender differences. Results: Overall, more women attended than men. By age bands, more 15–19 year old women than men attended (23.3% vs 12.5%, p<0.001) but, for all age-bands 20 years and older, men were at least as likely to attend as women. Further, for those aged 25– 29 years (20.3% vs 17%, p<0.5) and 45 years and older (11.9% vs 7.4%, p<0.001), more men than women of the same-age band were seen. Men who attended were more likely to self-refer (58.5% vs 43%, p<0.001) and less likely to be asymptomatic (30.3% vs 38.4%, p<0.001). Conclusions: Our data suggest men aged 20 years and older are at least, if not more, likely than women to attend a sexual health clinic for sexual health concerns. However, there appears to be under-utilisation by younger men. To improve sexual health for men and women, help-seeking must be timely and effective. We need to better understand and address sexual healthcare barriers for young men

A note on the probability of generating alternating or symmetric groups

We improve on recent estimates for the probability of generating the alternating and symmetric groups $\mathrm{Alt}(n)$ and $\mathrm{Sym}(n)$. In particular we find the sharp lower bound, if the probability is given by a quadratic in $n^{-1}$. This leads to improved bounds on the largest number $h(\mathrm{Alt}(n))$ such that a direct product of $h(\mathrm{Alt}(n))$ copies of $\mathrm{Alt}(n)$ can be generated by two elements

Models for discriminating image blur from loss of contrast

Observers can discriminate between blurry and low-contrast images (Morgan, 2017). Wang and Simoncelli (2004) demonstrated that a code for blur is inherent to the phase relationships between localized pattern detectors of different scale. To test whether human observers actually use local phase coherence when discriminating between image blur and loss of contrast, we compared phase-scrambled chessboards with unscrambled chessboards. Although both stimuli had identical amplitude spectra, local phase coherence was disrupted by phase-scrambling. Human observers were required to concurrently detect and identify (as contrast or blur) image manipulations in the 2x2 forced-choice paradigm (Nachmias & Weber, 1975; Watson & Robson, 1981) traditionally considered to be a litmus test for "labelled lines" (i.e. detection mechanisms that can be distinguished on the basis of their preferred stimuli). Phase scrambling reduced some observers’ ability to discriminate between blur and a reduction in contrast. However, none of our observers produced data consistent with Watson & Robson’s most stringent test for labelled lines, regardless whether phases were scrambled or not. Models of performance fit significantly better when either a) the blur detector also responded to contrast modulations, b) the contrast detector also responded to blur modulations, or c) noise in the two detectors was anticorrelate