3,689 research outputs found
A novel method for searching the - mixing effect in the angular distribution analysis of a four-body decay
In this work, we raised a novel method for searching the
- mixing effect in an angular distribution
analysis of the decay, where the
mixing effect can be observed by the appearance of the resonant.
Armed with this angular distribution, the decay branching fraction and the
forward-backward asymmetry are predicted. We pointed out that the
forward-backward asymmetry, as a function of the invariant mass square of
and the - mixing angle
, can be used to distinguish the two resonants and
even provide a possibility to determine the exact mixing angle.Comment: 7 pages, 3 figure
Phylogenomic reconstruction of lactic acid bacteria: an update
<p>Abstract</p> <p>Background</p> <p>Lactic acid bacteria (LAB) are important in the food industry for the production of fermented food products and in human health as commensals in the gut. However, the phylogenetic relationships among LAB species remain under intensive debate owing to disagreements among different data sets.</p> <p>Results</p> <p>We performed a phylogenetic analysis of LAB species based on 232 genes from 28 LAB genome sequences. Regardless of the tree-building methods used, combined analyses yielded an identical, well-resolved tree topology with strong supports for all nodes. The LAB species examined were divided into two groups. Group 1 included families Enterococcaceae and Streptococcaceae. Group 2 included families Lactobacillaceae and Leuconostocaceae. Within Group 2, the LAB species were divided into two clades. One clade comprised of the acidophilus complex of genus <it>Lactobacillus </it>and two other species, <it>Lb. sakei </it>and <it>Lb. casei</it>. In the acidophilus complex, <it>Lb. delbrueckii </it>separated first, while <it>Lb. acidophilus</it>/<it>Lb. helveticus </it>and <it>Lb. gasseri</it>/<it>Lb. johnsonii </it>were clustered into a sister group. The other clade within Group 2 consisted of the salivarius subgroup, including five species, <it>Lb. salivarius</it>, <it>Lb. plantarum</it>, <it>Lb. brevis</it>, <it>Lb. reuteri</it>, <it>Lb. fermentum</it>, and the genera <it>Pediococcus, Oenococcus</it>, and <it>Leuconostoc</it>. In this clade, <it>Lb. salivarius </it>was positioned most basally, followed by two clusters, one corresponding to <it>Lb. plantarum</it>/<it>Lb. brevis </it>pair and <it>Pediococcus</it>, and the other including <it>Oenococcus</it>/<it>Leuconostoc </it>pair and <it>Lb. reuteri</it>/<it>Lb. fermentum </it>pair. In addition, phylogenetic utility of the 232 genes was analyzed to identify those that may be more useful than others. The genes identified as useful were related to translation and ribosomal structure and biogenesis (TRSB), and a three-gene set comprising genes encoding ultra-violet resistance protein B (<it>uvrB</it>), DNA polymerase III (<it>polC</it>) and penicillin binding protein 2B (<it>pbpB</it>).</p> <p>Conclusions</p> <p>Our phylogenomic analyses provide important insights into the evolution and diversification of LAB species, and also revealed the phylogenetic utility of several genes. We infer that the occurrence of multiple, independent adaptation events in LAB species, have resulted in their occupation of various habitats. Further analyses of more genes from additional, representative LAB species are needed to reveal the molecular mechanisms underlying adaptation of LAB species to various environmental niches.</p
Are gravitational wave ringdown echoes always equal-interval ?
Gravitational wave (GW) ringdown waveforms may contain "echoes" that encode
new physics in the strong gravity regime. It is commonly assumed that the new
physics gives rise to the GW echoes whose intervals are constant. We point out
that this assumption is not always applicable. In particular, if the
post-merger object is initially a wormhole, which slowly pinches off and
eventually collapses into a black hole, the late-time ringdown waveform exhibit
a series of echoes whose intervals are increasing with time. We also assess how
this affects the ability of Advanced LIGO/Virgo to detect these new signals.Comment: 10 pages,5 figure
Detection of gamma-ray emission from the Coma cluster with Fermi Large Area Telescope and tentative evidence for an extended spatial structure
Many galaxy clusters have giant halos of non-thermal radio emission,
indicating the presence of relativistic electrons in the clusters. Relativistic
protons may also be accelerated by merger and/or accretion shocks in galaxy
clusters. These cosmic-ray (CR) electrons and/or protons are expected to
produce gamma-rays through inverse-Compton scatterings or inelastic
collisions respectively. Despite of intense efforts in searching for
high-energy gamma-ray emission from galaxy clusters, conclusive evidence is
still missing so far. Here we report the discovery of MeV gamma-ray
emission from the Coma cluster direction with an unbinned likelihood analysis
of the 9 years of {\it Fermi}-LAT Pass 8 data. The gamma-ray emission shows a
spatial morphology roughly coincident with the giant radio halo, with an
apparent excess at the southwest of the cluster. Using the test statistic
analysis, we further find tentative evidence that the gamma-ray emission at the
Coma center is spatially extended. The extended component has an integral
energy flux of in the
energy range of 0.2 - 300 GeV and the spectrum is soft with a photon index of
. Interpreting the gamma-ray emission as arising from CR proton
interaction, we find that the volume-averaged value of the CR to thermal
pressure ratio in the Coma cluster is about . Our results show that
galaxy clusters are likely a new type of GeV gamma-ray sources, and they are
probably also giant reservoirs of CR protons.Comment: 10 pages, 10 figures, Accepted by Physical Review D, more spatial
models for the gamma-ray emission are used, systematic checks on the results
are adde
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