178 research outputs found
The Dark Disk of the Milky Way
Massive satellite accretions onto early galactic disks can lead to the
deposition of dark matter in disk-like configurations that co-rotate with the
galaxy. This phenomenon has potentially dramatic consequences for dark matter
detection experiments. We utilize focused, high-resolution simulations of
accretion events onto disks designed to be Galaxy analogues, and compare the
resultant disks to the morphological and kinematic properties of the Milky
Way's thick disk in order to bracket the range of co-rotating accreted dark
matter. We find that the Milky Way's merger history must have been unusually
quiescent compared to median LCDM expectations and therefore its dark disk must
be relatively small: the fraction of accreted dark disk material near the Sun
is about 20% of the host halo density or smaller and the co-rotating dark
matter fraction near the Sun, defined as particles moving with a rotational
velocity lag less than 50 km/s, is enhanced by about 30% or less compared to a
standard halo model. Such a dark disk could contribute dominantly to the low
energy (of order keV for a dark matter particle with mass 100 GeV) nuclear
recoil event rate of direct dectection experiments, but it will not change the
likelihood of detection significantly. These dark disks provide testable
predictions of weakly-interacting massive particle dark matter models and
should be considered in detailed comparisons to experimental data. Our findings
suggest that the dark disk of the Milky Way may provide a detectable signal for
indirect detection experiments, contributing up to about 25% of the dark matter
self-annihilation signal in the direction of the center of the Galaxy, lending
the signal a noticeably oblate morphology.Comment: 11 pages, 6 figures, 1 table; submitted to Ap
The Medial Olivocochlear Reflex Is Unlikely to Play a Role in Listening Difficulties in Children
The medial olivocochlear reflex (MOCR) has been implicated in several auditory processes. The putative role of the MOCR in improving speech perception in noise is particularly relevant for children who complain of listening difficulties (LiD). The hypothesis that the MOCR may be impaired in individuals with LiD or auditory processing disorder has led to several investigations but without consensus. In two related studies, we compared the MOCR functioning of children with LiD and typically developing (TD) children in the same age range (7–17 years). In Study 1, we investigated ipsilateral, contralateral, and bilateral MOCR using forward-masked click-evoked otoacoustic emissions (CEOAEs; n = 17 TD, 17 LiD). In Study 2, we employed three OAE types: CEOAEs (n = 16 TD, 21 LiD), stimulus frequency OAEs (n = 21 TD, 30 LiD), and distortion product OAEs (n = 17 TD, 22 LiD) in a contralateral noise paradigm. Results from both studies suggest that the MOCR functioning is not significantly different between the two groups. Some likely reasons for differences in findings among published studies could stem from the lack of strict data quality measures (e.g., high signal-to-noise ratio, control for the middle ear muscle reflex) that were enforced in the present study. The inherent variability of the MOCR, the subpar reliability of current MOCR methods, and the heterogeneity in auditory processing deficits that underlie auditory processing disorder make detecting clinically relevant differences in MOCR function impractical using current methods
The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias
Dark matter halo clustering depends not only on halo mass, but also on other
properties such as concentration and shape. This phenomenon is known broadly as
assembly bias. We explore the dependence of assembly bias on halo definition,
parametrized by spherical overdensity parameter, . We summarize the
strength of concentration-, shape-, and spin-dependent halo clustering as a
function of halo mass and halo definition. Concentration-dependent clustering
depends strongly on mass at all . For conventional halo definitions
(), concentration-dependent clustering
at low mass is driven by a population of haloes that is altered through
interactions with neighbouring haloes. Concentration-dependent clustering can
be greatly reduced through a mass-dependent halo definition with for haloes with . Smaller implies larger radii and
mitigates assembly bias at low mass by subsuming altered, so-called backsplash
haloes into now larger host haloes. At higher masses () larger overdensities, , are necessary. Shape- and spin-dependent clustering are
significant for all halo definitions that we explore and exhibit a relatively
weaker mass dependence. Generally, both the strength and the sense of assembly
bias depend on halo definition, varying significantly even among common
definitions. We identify no halo definition that mitigates all manifestations
of assembly bias. A halo definition that mitigates assembly bias based on one
halo property (e.g., concentration) must be mass dependent. The halo
definitions that best mitigate concentration-dependent halo clustering do not
coincide with the expected average splashback radii at fixed halo mass.Comment: 19 pages, 13 figures. Updated to published version. Main result
summarized in Figure 1
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