571 research outputs found
Electromagnetic Leptogenesis
We present a new leptogenesis scenario, where the lepton asymmetry is
generated by CP violating decays of heavy electroweak singlet neutrinos via
electromagnetic dipole moment couplings to the ordinary light neutrinos. Akin
to the usual scenario where the decays are mediated through Yukawa
interactions, we have shown, by explicit calculations, that the desired
asymmetry can be produced through the interference of the corresponding
tree-level and one-loop decay amplitudes involving the effective dipole moment
operators. We also find that the relationship of the leptogenesis scale to the
light neutrino masses is similar to that for the standard Yukawa-mediated
mechanism.Comment: 6 pages, 6 figures; v2: some references added, minor change to
discussion, accepted by PR
Generation of entangled states and error protection from adiabatic avoided level crossings
We consider the environment-affected dynamics of self-interacting
particles living in one-dimensional double wells. Two topics are dealt with.
First, we consider the production of entangled states of two-level systems. We
show that by adiabatically varying the well biases we may dynamically generate
maximally entangled states, starting from initially unentangled product states.
Entanglement degradation due to a common type of environmental influence is
then computed by solving a master equation. However, we also demonstrate that
entanglement production is unaffected if the system-environment coupling is of
the type that induces ``motional narrowing''. As our second but related topic,
we construct a different master equation that seamlessly merges error
protection/detection dynamics for quantum information with the environmental
couplings responsible for producing the errors in the first place. Adiabatic
avoided crossing schemes are used in both topics.Comment: 14 pages, 6 figures. Minor changes. To appear in Phys. Rev.
Dynamic responses of B acteroides thetaiotaomicron during growth on glycan mixtures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98163/1/mmi12228-sup-0001-si.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/98163/2/mmi12228.pd
Stringent Constraints on Cosmological Neutrino-Antineutrino Asymmetries from Synchronized Flavor Transformation
We assess a mechanism which can transform neutrino-antineutrino asymmetries
between flavors in the early universe, and confirm that such transformation is
unavoidable in the near bi-maximal framework emerging for the neutrino mixing
matrix. We show that the process is a standard Mikheyev-Smirnov-Wolfenstein
flavor transformation dictated by a synchronization of momentum states. We also
show that flavor ``equilibration'' is a special feature of maximal mixing, and
carefully examine new constraints placed on neutrino asymmetries. In
particular, the big bang nucleosynthesis limit on electron neutrino degeneracy
xi_e < 0.04 does not apply directly to all flavors, yet confirmation of the
large-mixing-angle solution to the solar neutrino problem will eliminate the
possibility of degenerate big bang nucleosynthesis.Comment: 11 pages, 6 figures; minor changes to match PRD versio
Assessing five decades of garden bee studies
Urban garden spaces are potentially important habitats for bee conservation. Gardens can host diverse flora, which provide floral resources across foraging seasons for bee species. Recent reviews have focused on the impacts of cityscapes on urban bee assemblages in different green spaces. Urban gardens are distinct from other urban green spaces, and bee communities in urban spaces have been an increasing topic of study over the past few decades. We reviewed 28 urban garden bee studies spanning five decades and 14 countries to compile an original metadataset of bee species' functional traits to understand the conservation value of gardens, identify gaps in bee sampling efforts, and summarize the calls to action included by their authors. Studies of urban garden bees have documented between 674 (conservative count, excluding morphospecies) and 830 (liberal count, including morphospecies) bee species. Urban garden bee communities were taxonomically and functionally diverse, although bee species that were non-eusocial, ground-nesting, generalist foragers, and native were most common in garden habitats. The proportion of parasitic bee species and specialist foragers found in urban gardens was comparable to proportions for global bee taxa. This suggests that gardens contain the hosts and forage needed to support bees with specialized life history requirements, and thus represent high quality habitat for a subset of bee communities. Garden bee research was strongly biased toward the northern hemisphere, which signifies a large gap in our understanding of garden bee communities in other regions. The variety of, and non-standard sampling methods in garden bee research makes it difficult to directly compare results between studies. In addition, both intentional low taxonomic resolution and a lack of collaboration with taxonomists constrains our understanding of bee diversity. Our analyses highlight both successes of past urban garden bee studies, and areas of opportunity for future research as we move into a sixth decade of garden bee research
W/Z Bremsstrahlung as the Dominant Annihilation Channel for Dark Matter
Dark matter annihilation to leptons, , is
necessarily accompanied by electroweak radiative corrections, in which a W or Z
boson is radiated from a final state particle. Given that the W and Z gauge
bosons decay dominantly via hadronic channels, it is thus impossible to produce
final state leptons without accompanying protons, antiprotons, and gamma rays.
Significantly, while many dark matter models feature a helicity suppressed
annihilation rate to fermions, radiating a massive gauge boson from a final
state fermion removes this helicity suppression, such that the branching ratios
Br(l \nu W), Br(l^+l^- Z), and Br(\nu\nubar Z) dominate over Br(l\bar{l}).
W/Z-bremsstrahlung thus allows indirect detection of many WIMP models that
would otherwise be helicity-suppressed, or v^2 suppressed. Antiprotons and even
anti-deuterons become consequential final state particles. This is an important
result for future DM searches. We discuss the implications of
W/Z-bremsstrahlung for "leptonic" DM models which aim to fit recent cosmic ray
positron and antiproton data.Comment: 19 pages, 5 figures. Updated to include Erratum, and changes made to
PRD versio
Infiltration efficiency and subsurface water processes of a sustainable drainage system and consequences to flood management
With increased intensity rainfall events globally and urban expansion decreasing permeable surfaces, there is an increasing problem of urban flooding. This study aims to better understand rainfall infiltration into a Sustainable Drainage System (SuDS) permeable pavement, compared with an adjacent Green Area of made ground, in relationship to groundwater levels below both areas. Both areas were instrumented with soil water content and matric potential sensors and four shallow boreholes were instrumented with groundwater level sensors. Surface infiltration rates were measured using a double‐ring infiltrometer. Results showed that average infiltration rates of the SuDS (1,925 mm/hr) were significantly higher than the Green Area (56 mm/hr). The SuDS was well designed to transfer rainfall rapidly to the aquifer below, where groundwater levels rapidly rose within 1 hr of a 1 in 30 year event (32.8 mm/hr). In comparison, soil compaction of the made ground Green Area decreased infiltration rates, but still enabled the majority of rainfall events to infiltrate. The aquifer below the Green Area responded more slowly, as lower matrix potentials facilitated water retention in the soil profile, slowing water draining to the aquifer. This work reiterates the importance of ensuring a 1 m separation depth between the base of the SuDS infiltration zone and aquifer depth
Do solar neutrinos decay?
Despite the fact that the solar neutrino flux is now well-understood in the
context of matter-affected neutrino mixing, we find that it is not yet possible
to set a strong and model-independent bound on solar neutrino decays. If
neutrinos decay into truly invisible particles, the Earth-Sun baseline defines
a lifetime limit of \tau/m \agt 10^{-4} s/eV. However, there are many
possibilities which must be excluded before such a bound can be established.
There is an obvious degeneracy between the neutrino lifetime and the mixing
parameters. More generally, one must also allow the possibility of active
daughter neutrinos and/or antineutrinos, which may partially conceal the
characteristic features of decay. Many of the most exotic possibilities that
presently complicate the extraction of a decay bound will be removed if the
KamLAND reactor antineutrino experiment confirms the large-mixing angle
solution to the solar neutrino problem and measures the mixing parameters
precisely. Better experimental and theoretical constraints on the B
neutrino flux will also play a key role, as will tighter bounds on absolute
neutrino masses. Though the lifetime limit set by the solar flux is weak, it is
still the strongest direct limit on non-radiative neutrino decay. Even so,
there is no guarantee (by about eight orders of magnitude) that neutrinos from
astrophysical sources such as a Galactic supernova or distant Active Galactic
Nuclei will not decay.Comment: Very minor corrections, corresponds to published versio
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
Eight common genetic variants associated with serum dheas levels suggest a key role in ageing mechanisms
Dehydroepiandrosterone sulphate (DHEAS) is the most abundant circulating steroid secreted by adrenal glands-yet its function is unknown. Its serum concentration declines significantly with increasing age, which has led to speculation that a relative DHEAS deficiency may contribute to the development of common age-related diseases or diminished longevity. We conducted a meta-analysis of genome-wide association data with 14,846 individuals and identified eight independent common SNPs associated with serum DHEAS concentrations. Genes at or near the identified loci include ZKSCAN5 (rs11761528; p = 3.15×10-36), SULT2A1 (rs2637125; p = 2.61×10-19), ARPC1A (rs740160; p = 1.56×10-16), TRIM4 (rs17277546; p = 4.50×10-11), BMF (rs7181230; p = 5.44×10-11), HHEX (rs2497306; p = 4.64×10-9), BCL2L11 (rs6738028; p = 1.72×10-8), and CYP2C9 (rs2185570; p = 2.29×10-8). These genes are associated with type 2 diabetes, lymphoma, actin filament assembly, drug and xenobiotic metabolism, and zinc finger proteins. Several SNPs were associated with changes in gene expression levels, and the related genes are connected to biological pathways linking DHEAS with ageing. This study provides much needed insight into the function of DHEAS
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