365 research outputs found
Turning off the Lights: How Dark is Dark Matter?
We consider current observational constraints on the electromagnetic charge
of dark matter. The velocity dependence of the scattering cross-section through
the photon gives rise to qualitatively different constraints than standard dark
matter scattering through massive force carriers. In particular, recombination
epoch observations of dark matter density perturbations require that
, the ratio of the dark matter to electronic charge, is less than
for , rising to for .
Though naively one would expect that dark matter carrying a charge well below
this constraint could still give rise to large scattering in current direct
detection experiments, we show that charged dark matter particles that could be
detected with upcoming experiments are expected to be evacuated from the
Galactic disk by the Galactic magnetic fields and supernova shock waves, and
hence will not give rise to a signal. Thus dark matter with a small charge is
likely not a source of a signal in current or upcoming dark matter direct
detection experiments.Comment: 19 pages, 2 figures; v2 - figures fixed, references adde
Sommerfeld Enhancements for Thermal Relic Dark Matter
The annihilation cross section of thermal relic dark matter determines both
its relic density and indirect detection signals. We determine how large
indirect signals may be in scenarios with Sommerfeld-enhanced annihilation,
subject to the constraint that the dark matter has the correct relic density.
This work refines our previous analysis through detailed treatments of resonant
Sommerfeld enhancement and the effect of Sommerfeld enhancement on freeze out.
Sommerfeld enhancements raise many interesting issues in the freeze out
calculation, and we find that the cutoff of resonant enhancement, the
equilibration of force carriers, the temperature of kinetic decoupling, and the
efficiency of self-interactions for preserving thermal velocity distributions
all play a role. These effects may have striking consequences; for example, for
resonantly-enhanced Sommerfeld annihilation, dark matter freezes out but may
then chemically recouple, implying highly suppressed indirect signals, in
contrast to naive expectations. In the minimal scenario with standard
astrophysical assumptions, and tuning all parameters to maximize the signal, we
find that, for force-carrier mass m_phi = 250 MeV and dark matter masses m_X =
0.1, 0.3, and 1 TeV, the maximal Sommerfeld enhancement factors are S_eff = 7,
30, and 90, respectively. Such boosts are too small to explain both the PAMELA
and Fermi excesses. Non-minimal models may require smaller boosts, but the
bounds on S_eff could also be more stringent, and dedicated freeze out analyses
are required. For concreteness, we focus on 4 mu final states, but we also
discuss 4 e and other modes, deviations from standard astrophysical assumptions
and non-minimal particle physics models, and we outline the steps required to
determine if such considerations may lead to a self-consistent explanation of
the PAMELA or Fermi excesses.Comment: 31 pages, published versio
Study of CP violation in decay
In this paper, we study CP violation in and
decays, where and denote a light spin-1/2 baryon,
pseudoscalar and a vector meson respectively. In these processes the odd CP
violating triple-product (TP) correlations are examined. The genuine CP
violating observables which are composed of the helicity amplitudes occurring
in the angular distribution are constructed. Experimentally, by performing a
full angular analysis it is shown how one may extract the helicity amplitudes
and then obtain the TP asymmetries. We estimate the TP asymmetries in \lam
decays to be negligible in the standard model making these processes an
excellent place to look for new physics. Taking a two Higgs doublet model, as
an example of new physics, we show that large TP asymmetries are possible in
these decays. Finally, we discuss how BES-III and Super -Charm
experiments will be sensitive to these CP violating signals in
decays.Comment: 7 pages, 2 tables. Journal reference is adde
An Updated Search of Steady TeV Ray Point Sources in Northern Hemisphere Using the Tibet Air Shower Array
Using the data taken from Tibet II High Density (HD) Array (1997
February-1999 September) and Tibet-III array (1999 November-2005 November), our
previous northern sky survey for TeV ray point sources has now been
updated by a factor of 2.8 improved statistics. From to
in declination (Dec) range, no new TeV ray point
sources with sufficiently high significance were identified while the
well-known Crab Nebula and Mrk421 remain to be the brightest TeV ray
sources within the field of view of the Tibet air shower array. Based on the
currently available data and at the 90% confidence level (C.L.), the flux upper
limits for different power law index assumption are re-derived, which are
approximately improved by 1.7 times as compared with our previous reported
limits.Comment: This paper has been accepted by hepn
AI protein structure prediction-based modeling and mutagenesis of a protostome receptor and peptide ligands reveal key residues for their interaction
The protostome leucokinin (LK) signaling system, including LK peptides and their G protein-coupled receptors, has been characterized in several species. Despite the progress, molecular mechanisms governing LK peptide–receptor interactions remain to be elucidated. Previously, we identified a precursor protein for Aplysia leucokinin-like peptides (ALKs) that contains the greatest number of amidated peptides among LK precursors in all species identified so far. Here, we identified the first ALK receptor from Aplysia, ALKR. We used cell-based IP1 activation assays to demonstrate that two ALK peptides with the most copies, ALK1 and ALK2, activated ALKR with high potencies. Other endogenous ALK-derived peptides bearing the FXXWX-amide motif also activated ALKR to various degrees. Our examination of cross-species activity of ALKs with the Anopheles LK receptor was consistent with a critical role for the FXXWX-amide motif in receptor activity. Furthermore, we showed, through alanine substitution of ALK1, the highly conserved phenylalanine (F), tryptophan (W), and C-terminal amidation were each essential for receptor activation. Finally, we used an artificial intelligence– based protein structure prediction server (Robetta) and Autodock Vina to predict the ligand-bound conformation of ALKR. Our model predicted several interactions (i.e., hydrophobic interactions, hydrogen bonds, and amide-pi stacking) between ALK peptides and ALKR, and several of our substitution and mutagenesis experiments were consistent with the predicted model. In conclusion, our results provide important information defining possible interactions between ALK peptides and their receptors. The workflow utilized here may be useful for studying other ligand–receptor interactions for a neuropeptide signaling system, particularly in protostomes
Inhibitory role of peroxisome proliferator-activated receptor gamma in hepatocarcinogenesis in mice and in vitro
Although peroxisome proliferator-activated receptor gamma (PPARγ) agonist have been shown to inhibit hepatocellular carcinoma (HCC) development, the role of PPARγ in hepatocarcinogenesis remains unclear. We investigated the therapeutic efficacy of PPAR
A possible signature of new physics at BES-III
The recent observations of the purely leptonic decay \Ds \to \mu^+
\nu_{\mu} and at CLEO-c and factory may allow a
possible contribution from a charged Higgs boson. One such measurement of the
decay constant differs from the most precise unquenched lattice QCD
calculation by 4 level. Meanwhile, the measured ratio, {\cal BR}(\Ds
\to \mu^+ \nu_{\mu}) / {\cal BR}(\Dp \to \mu^+ \nu_{\mu}), is larger than
the standard model prediction at 2.0 level. We discuss that the precise
measurement of the ratio {\cal BR}(\Ds \to \mu^+ \nu_{\mu}) / {\cal BR}(\Dp
\to \mu^+ \nu_{\mu}) at BES-III will shed light on the presence of new
intermediate particles by comparing the theoretical predictions, especially,
the predictions of high precise unquenched lattice QCD calculation.Comment: 5 pages, 3 figures, mini-review, accepted by Chinese Physics C (HEP &
NP
BCAR1 Protein Plays Important Roles in Carcinogenesis and Predicts Poor Prognosis in Non-Small-Cell Lung Cancer
Objective: Our previous study suggested the potential clinical implications of BCAR1 in non-small-cell lung cancer (NSCLC) (Mol Diagn Ther. 2011. 15(1): 31–40). Herein, we aim to evaluate the predictive power of BCAR1 as a marker for poor prognosis in NSCLC cases, verify the carcinogenic roles of BCAR1 in the A549 lung adenocarcinoma cell line, and testify to the BCAR1/phospho-p38 axis. Methods: Between January 2006 and June 2010, there were a total of 182 patients with NSCLC (151 cases with available follow up data, and 31 cases lost to follow-up due to the invalid contact information). We inspected BCAR1, phospho-BCAR1(Tyr410), phospho-p38(Thr180/Tyr182) and p38 expression in NSCLC tissues and matched adjacent normal tissues by immunoblotting and IHC. After BCAR1-RNA interference in A549 cells, we inspected the protein expression (BCAR1, phospho-BCAR1, phospho-p38 and p38) and performed cell biology experiments (cell growth, migration and cycle). Results: BCAR1 was overexpressed in NSCLC tissues (177/182) and cell lines (A549 and Calu-3). However, it was not detected in the normal adjacent tissue in 161 of the 182 cases. Higher BCAR1 levels were strongly associated with more poorly differentiated NSCLC and predicted poorer prognosis. BCAR1 knockdown caused cell growth arrest, cell migration inhibition and cell cycle arrest of A549 cells. Overexpression of BCAR1 was associated with activation of p38 in NSCLC cases, and BCAR1 knockdown caused reduction of phospho-p38 levels in A549 cells
Oscillating Asymmetric Dark Matter
We study the dynamics of dark matter (DM) particle-antiparticle oscillations
within the context of asymmetric DM. Oscillations arise due to small DM
number-violating Majorana-type mass terms, and can lead to recoupling of
annihilation after freeze-out and washout of the DM density. We derive the
density matrix equations for DM oscillations and freeze-out from first
principles using nonequilibrium field theory, and our results are qualitatively
different than in previous studies. DM dynamics exhibits
particle-vs-antiparticle "flavor" effects, depending on the interaction type,
analogous to neutrino oscillations in a medium. "Flavor-sensitive" DM
interactions include scattering or annihilation through a new vector boson,
while "flavor-blind" interactions include scattering or s-channel annihilation
through a new scalar boson, or annihilation to pairs of bosons. In particular,
we find that flavor-sensitive annihilation does not recouple when coherent
oscillations begin, and that flavor-blind scattering does not lead to
decoherence.Comment: 23 pages, 4 figures, A typo fixed, References adde
Comparison of Double Kissing Crush Versus Culotte Stenting for Unprotected Distal Left Main Bifurcation Lesions Results From a Multicenter, Randomized, Prospective DKCRUSH-III Study
ObjectivesThe study aimed to investigate the difference in major adverse cardiac event (MACE) at 1-year after double kissing (DK) crush versus Culotte stenting for unprotected left main coronary artery (UPLMCA) distal bifurcation lesions.BackgroundDK crush and Culotte stenting were reported to be effective for treatment of coronary bifurcation lesions. However, their comparative performance in UPLMCA bifurcation lesions is not known.MethodsA total of 419 patients with UPLMCA bifurcation lesions were randomly assigned to DK (n = 210) or Culotte (n = 209) treatment. The primary endpoint was the occurrence of a MACE at 1 year, including cardiac death, myocardial infarction, and target vessel revascularization (TVR). In-stent restenosis (ISR) at 8 months was secondary endpoint, and stent thrombosis (ST) served as a safety endpoint. Patients were stratified by SYNTAX (Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery) and NERS (New Risk Stratification) scores.ResultsPatients in the Culotte group had significant higher 1-year MACE rate (16.3%), mainly driven by increased TVR (11.0%), compared with the DK group (6.2% and 4.3%, respectively; all p < 0.05). ISR rate in side branch was 12.6% in the Culotte group and 6.8% in the DK group (p = 0.037). Definite ST rate was 1.0% in the Culotte group and 0% in the DK group (p = 0.248). Among patients with bifurcation angle ≥70°, NERS score ≥20, and SYNTAX score ≥23, the 1-year MACE rate in the DK group (3.8%, 9.2%, and 7.1%, respectively) was significantly different to those in the Culotte group(16.5%, 20.4%, and 18.9%, respectively; all p < 0.05).ConclusionsCulotte stenting for UPLMCA bifurcation lesions was associated with significantly increased MACEs, mainly due to the increased TVR. (Double Kissing [DK] Crush Versus Culotte Stenting for the Treatment of Unprotected Distal Left Main Bifurcation Lesions: DKCRUSH-III, a Multicenter Randomized Study Comparing Double-Stent Techniques; ChiCTR-TRC-00000151
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