363 research outputs found
Anticipating the XRISM search for the decay of resonantly produced sterile neutrino dark matter
The resonantly produced sterile neutrino () of the neutrino minimal
standard model (MSM) is a compelling dark matter candidate, especially in
the reported possible detection of with mass ~keV in
X-ray decay. This particle will be accessible to the XRISM X-ray mission over
the next 12 months. We revisit the physics behind and the uncertainty in
its parameters. We compare predictions for the keV
mixing angle, , and half-mode mass, , to
existing X-ray observations and structure formation constraints. The strongest
available constraints rule out as a dark matter candidate, and a more
optimistic reading of the data prefers and
. We highlight that the most
promising upcoming opportunity for a detection is to find a line of velocity
dispersion in the Virgo cluster with XRISM, and
then draw up a list of future objects of study to determine: (i) whether the
line is from dark matter generally, and (ii) if from dark matter, whether that
candidate is indeed .Comment: 13 pages, 7 figures. To be submitted to MNRAS. Contact: [email protected]
Halo assembly in cold and warm dark matter during the JWST frontier epoch
The JWST mission is in the process of probing the galaxy mass function at
, when conceivably any delay in halo assembly due to the presence of a
dwarf galaxy-scale power spectrum cutoff may drastically suppress the number of
galaxies relative to the cold dark matter (CDM) expectation. We employ N-body
simulations of CDM and warm dark matter (WDM) to explore how the difference in
halo collapse time between these models scales with descendant halo mass.
We demonstrate that collapse begins first for the most massive haloes, and the
delay in collapse time between CDM and WDM haloes correlates inversely with
descendant mass. We thus infer that only present-day dwarf galaxies exhibit any
difference in their assembly history between CDM and WDM at , and
therefore support previous studies that have found JWST is unlikely to
determine whether our Universe is better described by the CDM cosmology or the
WDM cosmology without favourable lensing studies.Comment: 9 pages, 6 figures, to be submitted to MNRAS. Contact: [email protected]
Oxidative DNA damage in mild cognitive impairment and late-stage Alzheimer's disease
Increasing evidence supports a role for oxidative DNA damage in aging and several neurodegenerative diseases including Alzheimer's disease (AD). Attack of DNA by reactive oxygen species (ROS), particularly hydroxyl radicals, can lead to strand breaks, DNA–DNA and DNA–protein cross-linking, and formation of at least 20 modified bases adducts. In addition, α,β-unsaturated aldehydic by-products of lipid peroxidation including 4-hydroxynonenal and acrolein can interact with DNA bases leading to the formation of bulky exocyclic adducts. Modification of DNA bases by direct interaction with ROS or aldehydes can lead to mutations and altered protein synthesis. Several studies of DNA base adducts in late-stage AD (LAD) brain show elevations of 8-hydroxyguanine (8-OHG), 8-hydroxyadenine (8-OHA), 5-hydroxycytosine (5-OHC), and 5-hydroxyuracil, a chemical degradation product of cytosine, in both nuclear and mitochondrial DNA (mtDNA) isolated from vulnerable regions of LAD brain compared to age-matched normal control subjects. Previous studies also show elevations of acrolein/guanine adducts in the hippocampus of LAD subjects compared to age-matched controls. In addition, studies of base excision repair show a decline in repair of 8-OHG in vulnerable regions of LAD brain. Our recent studies show elevated 8-OHG, 8-OHA, and 5,6-diamino-5-formamidopyrimidine in both nuclear and mtDNA isolated from vulnerable brain regions in amnestic mild cognitive impairment, the earliest clinical manifestation of AD, suggesting that oxidative DNA damage is an early event in AD and is not merely a secondary phenomenon
Oxidative DNA Damage in Mild Cognitive Impairment and Late-Stage Alzheimer\u27s Disease
Increasing evidence supports a role for oxidative DNA damage in aging and several neurodegenerative diseases including Alzheimer\u27s disease (AD). Attack of DNA by reactive oxygen species (ROS), particularly hydroxyl radicals, can lead to strand breaks, DNA–DNA and DNA–protein cross-linking, and formation of at least 20 modified bases adducts. In addition, α,β-unsaturated aldehydic by-products of lipid peroxidation including 4-hydroxynonenal and acrolein can interact with DNA bases leading to the formation of bulky exocyclic adducts. Modification of DNA bases by direct interaction with ROS or aldehydes can lead to mutations and altered protein synthesis. Several studies of DNA base adducts in late-stage AD (LAD) brain show elevations of 8-hydroxyguanine (8-OHG), 8-hydroxyadenine (8-OHA), 5-hydroxycytosine (5-OHC), and 5-hydroxyuracil, a chemical degradation product of cytosine, in both nuclear and mitochondrial DNA (mtDNA) isolated from vulnerable regions of LAD brain compared to age-matched normal control subjects. Previous studies also show elevations of acrolein/guanine adducts in the hippocampus of LAD subjects compared to age-matched controls. In addition, studies of base excision repair show a decline in repair of 8-OHG in vulnerable regions of LAD brain. Our recent studies show elevated 8-OHG, 8-OHA, and 5,6-diamino-5-formamidopyrimidine in both nuclear and mtDNA isolated from vulnerable brain regions in amnestic mild cognitive impairment, the earliest clinical manifestation of AD, suggesting that oxidative DNA damage is an early event in AD and is not merely a secondary phenomenon
Gravothermal collapse of Self-Interacting Dark Matter halos as the Origin of Intermediate Mass Black Holes in Milky Way satellites
Milky Way (MW) satellites exhibit a diverse range of internal kinematics,
reflecting in turn a diverse set of subhalo density profiles. These profiles
include large cores and dense cusps, which any successful dark matter model
must explain simultaneously. A plausible driver of such diversity is
self-interactions between dark matter particles (SIDM) if the cross section
passes the threshold for the gravothermal collapse phase at the characteristic
velocities of the MW satellites. In this case, some of the satellites are
expected to be hosted by subhalos that are still in the classical SIDM core
phase, while those in the collapse phase would have cuspy inner profiles, with
a SIDM-driven intermediate mass black hole (IMBH) in the centre as a
consequence of the runaway collapse. We develop an analytical framework that
takes into account the cosmological assembly of halos and is calibrated to
previous simulations; we then predict the timescales and mass scales () for the formation of IMBHs in velocity-dependent SIDM (vdSIDM) models as
a function of the present-day halo mass, . Finally, we estimate the region
in the parameter space of the effective cross section and for a subclass
of vdSIDM models that result in a diverse MW satellite population, as well as
their corresponding fraction of SIDM-collapsed halos and those halos' inferred
IMBH masses. We predict the latter to be in the range
with a relation that has a similar slope, but lower
normalization, than the extrapolated empirical relation of super-massive black
holes found in massive galaxies.Comment: 18 pages, 9 figures, to be submitted to PRD. Contact: [email protected]
Decaying dark matter: the case for a deep X-ray observation of Draco
Recent studies of M31, the Galactic Centre (GC), and galaxy clusters have made tentative detections of an X-ray line at ∼3.5keV that could be produced by decaying dark matter. We use high-resolution simulations of the Aquarius project to predict the likely amplitude of the X-ray decay flux observed in the GC relative to that observed in M31, and also of the GC relative to other parts of the Milky Way halo and to dwarf spheroidal galaxies. We show that the reported detections from M31 and the GC are compatible with each other, and with upper limits arising from high galactic latitude observations, and imply a decay time τ∼1028 s. We argue that this interpretation can be tested with deep observations of dwarf spheroidal galaxies: in 95 per cent of our mock observations, a 1.3 Ms pointed observation of Draco with XMM-Newton will enable us to discover or rule out at the 3σ level an X-ray feature from dark matter decay at 3.5keV, for decay times τ<0.8×1028
Eggshell pigment composition covaries with phylogeny but not with life history or with nesting ecology traits of British passerines
No single hypothesis is likely to explain the diversity in eggshell coloration and patterning across birds, suggesting that eggshell appearance is most likely to have evolved to fulfill many nonexclusive functions. By controlling for nonindependent phylogenetic associations between related species, we describe this diversity using museum eggshells of 71 British breeding passerine species to examine how eggshell pigment composition and concentrations vary with phylogeny and with life-history and nesting ecology traits. Across species, concentrations of biliverdin and protoporphyrin, the two main pigments found in eggshells, were strongly and positively correlated, and both pigments strongly covaried with phylogenetic relatedness. Controlling for phylogeny, cavity-nesting species laid eggs with lower protoporphyrin concentrations in the shell, while higher biliverdin concentrations were associated with thicker eggshells for species of all nest types. Overall, these relationships between eggshell pigment concentrations and the biology of passerines are similar to those previously found in nonpasserine eggs, and imply that phylogenetic dependence must be considered across the class in further explanations of the functional significance of avian eggshell coloration
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