118388583
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 masses of mχ∼5–10  GeV, weakly interacting massive particles (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 5σ 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 the 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 103  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.
8787684
Determining the WIMP mass from a single direct detection experiment
The energy spectrum of nuclear recoils in Weakly Interacting Massive Particle (WIMP) direct detection experiments depends on the underlying WIMP mass (strongly for light WIMPs, weakly for heavy WIMPs). We discuss how the accuracy with which the WIMP mass could be determined by a single direct detection experiment depends on the detector configuration and the WIMP properties. In particular we examine the effects of varying the underlying WIMP mass, the detector target nucleus, exposure, energy threshold and maximum energy, the local velocity distribution and the background event rate and spectrum.
119021467
PRIMORDIAL BLACK HOLES AND EARLY COSMOLOGY
We describe the changes to the standard primordial black hole constraints on density perturbations if there are modifications to the standard cosmology between the time of formation and nucleosynthesis.
117989592
Extracting Information about WIMP Properties from Direct Detection Experiments: Astrophysical Uncertainties
WIMP direct detection experiments probe the ultra-local dark matter density and velocity distribution. We review how uncertainties in these quantities affect the accuracy with which the WIMP mass and cross-section can be constrained or determined.
16034831
Probing the width of the MACHO mass function
The simplest interpretation of the microlensing events observed towards the Large Magellanic Cloud is that approximately half of the mass of the Milky Way halo is in the form of MAssive Compact Halo Objects with $M \sim 0.5 M_{\odot}$. This poses severe problems for stellar MACHO candidates, and leads to the consideration of more exotic objects such as primordial black holes (PBHs). Constraining the MACHO mass function will shed light on their nature. Using the current data we find, for four halo models, the best fit delta-function, power law and PBH mass functions. The best fit PBH mass functions, despite having significant finite width, have likelihoods which are similar to, and for one particular halo model greater than, those of the best fit delta functions. We also find that if the correct halo model is known then $\sim$ 500 events will be sufficient to determine whether the MACHO mass function has significant width, and will also allow determination of the mass function parameters to $\sim 5%$.
55672557
WIMP physics with ensembles of direct-detection experiments
if dierent classes of experiments see consistent signals and infer the same WIMP properties. In this work, we review the ideas, methods, and status of direct-detection searches. We focus in particular on extracting WIMP physics (WIMP interactions and phase-space distribution) from direct-detection data in the early discovery days when multiple experiments see of order dozens to hundreds of events. To demonstrate the essential complementarity of dierent direct-detection experiments in this context, we create mock data intended to represent the data from the near-future Generation 2 experiments. We consider both conventional supersymmetry-inspired benchmark points (with spin-independent and -dependent elastic cross sections just below current limits), as well as benchmark points for other classes of models (inelastic and eective-operator paradigms). We also investigate the eect on parameter estimation of loosening or dropping the assumptions about the local WIMP phase-space distribution. We arrive at two main conclusions. Firstly, teasing out WIMP physics with experiments depends critically on having a wide set of detector target materials, spanning a large range of target nuclear masses and spin-dependent sensitivity. It is also highly desirable to obtain data from low-threshold experiments. Secondly, a general reconstruction of the local WIMP velocity distribution, which will only be achieved if there are multiple experiments using dierent target materials, is critical to obtaining a robust and unbiased estimate of the WIMP mass.
119497368
H I Emission and Absorption in the Southern Galactic Plane Survey
We present preliminary results from the Southern Galactic Plane Survey (SGPS) Test Region and Parkes data. As part of the pilot project for the Southern Galactic Plane Survey, observations of a Test Region (325·5 ◦ ≤ l ≤ 333·5 ◦ ; −0·5 ◦ ≤ b ≤ 3·5 ◦ ) were completed in December 1998. Single-dish observations of the full survey region (253 ◦ ≤ l ≤ 358 ◦ ; |b |≤ 1 ◦ ) with the Parkes Radio Telescope were completed in March 2000. We present a sample of SGPS H i data, with particular attention to the smallest- and largest-scale structures seen in absorption and emission, respectively. On the large scale, we detect many prominent H i shells. On the small scale, we note extremely compact, cold clouds seen in H i self-absorption. We explore how these two classes of objects probe opposite ends of the H i spatial power spectrum.
7431869
Magnetic fields and ionized gas in the inner galaxy: An outer scale for turbulence and the possible role of H II regions
We present an analysis of rotation measure (RM) fluctuations from the test region of the Southern Galactic Plane Survey (SGPS), along with emission measure (EM) fluctuations in the same field taken from the Southern H? Sky Survey Atlas. The structure function of RM fluctuations shows a relatively steep slope at small scales (1'-5'), a break in slope to a flatter structure function at intermediate scales (5'-60'), and a systematic variation of the strength of fluctuations as a function of position angle on the sky at the largest scales (60'-200'). The structure function of EM fluctuations shows similar behavior, although the lower resolution of the data prevents detection of a possible break in the spectrum. We interpret the anisotropy in RM/EM structure on large scales as resulting from a large-scale gradient in electron density (and possibly magnetic field) across the region. The break in the slope of the RM structure function at scales of ~5' can be explained by contributions from two spatially distinct magnetoionized screens, most likely in the Local and Carina spiral arms. The observed structure function then implies that the outer scale of RM fluctuations in these screens is ~2 pc. Such behavior is in striking contrast to the expectation that interstellar turbulence forms an unbroken spectrum from kiloparsec down to AU scales. We conclude that we have identified an additional source of enhanced turbulence, injected on scales of a few pc, possibly seen only in the Galactic plane. The most likely source of such turbulence is individual H II regions from relatively low mass stars, whose characteristic scale size is similar to the outer scale of turbulence inferred here. These sources may be the dominant source of density and velocity fluctuations in warm ionized gas in the Galactic plane.
20155571
Faraday rotation of the supernova remnant G296.5+10.0: Evidence for a Magnetized Progenitor Wind
We present spectropolarimetric radio images of the supernova remnant (SNR) G296.5+10.0 at frequencies near 1.4 GHz, observed with the Australia Telescope Compact Array. By applying rotation measure (RM) synthesis to the data, a pixel-by-pixel map of Faraday rotation has been produced for the entire remnant. We find G296.5+10.0 to have a highly ordered RM structure, with mainly positive RMs (mean RM of +28 rad m–2) on the eastern side and negative RMs (mean RM of –14 rad m–2) on the western side, indicating a magnetic field which is directed away from us on one side and toward us on the other. We consider several possible mechanisms for creating the observed RM pattern. Neither Faraday rotation in foreground interstellar gas nor in a homogeneous ambient medium swept up by the SNR shell can easily explain the magnitude and sign of the observed RM pattern. Instead, we propose that the observed RMs are the imprint of an azimuthal magnetic field in the stellar wind of the progenitor star. Specifically, we calculate that a swept-up magnetized wind from a red supergiant can produce RMs of the observed magnitude, while the azimuthal pattern of the magnetic field at large distances from the star naturally produces the anti-symmetric RM pattern observed. Expansion into such a wind can possibly also account for the striking bilateral symmetry of the SNR's radio and X-ray morphologies.
14950553
The cosmic ray distribution in sagittarius B
The H.E.S.S. instrument has observed a diffuse flux of ~TeV γ-rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region, suggesting that the γ-rays originate in collisions between cosmic-ray hadrons (CRHs) and ambient matter. Of particular interest, H.E.S.S. has detected γ-rays from the Sagittarius (Sgr) B molecular cloud complex. Prompted by the suggestion of a hadronic origin for the γ-rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed γ-rays). Intriguingly, we have uncovered nonthermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic-ray ionization rate is 10 times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (1) a hard (~E-2.2), high-energy (TeV) population of CRHs is unavoidably required by the H.E.S.S. γ-ray data, and (2) the remaining broadband, nonthermal phenomenology is explained either by a rather steep (~E-2.9) spectrum of primary electrons or a (~E-2.7) population of CRHs. Perhaps unsurprisingly, no single power-law population of either leptons or hadrons can explain the totality of broadband, nonthermal Sgr B phenomenology.
118680225
Ultra- and hyper-compact H ii regions at 20 GHz
We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultracompact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind r adio survey for hyper- and ultra-compact HII regions. We have followed up these sources with the Australia Telescope Compact Array to obtain H70� recombination line measurements, higher resolution images at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have determined sizes and recombination line temperatures as well as modeling the spectral energy distributions to determine emission measures. We have classified the sources as hyper-compact or ultra-compact on the basis of their physical parameters, in comparison with benchmark parameters from the literature. Several of these bright, compact sources are potential cali brators for the Low Frequency Instrument (30 70 GHz) and the 100-GHz channel of the High Frequency Instrument of the Planck satellite mission. They may also be useful as calibrators for the Australia Telescope Compact Array, which lacks good non-variable primary flux ca librators at higher frequencies and in the Galactic plane region. Our spectral energy distri butions allow the flux densities within the Planck bands to be determined, although our high frequency observations show that several sources have excess emission at 95 GHz (3 mm) that can not be explained by current models.