2,051 research outputs found

    The Origin of the Arches Stellar Cluster Mass Function

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    We investigate the time evolution of the mass distribution of pre-stellar cores (PSCs) and their transition to the initial stellar mass function (IMF) in the central parts of a molecular cloud (MC) under the assumption that the coalescence of cores is important. Our aim is to explain the observed shallow IMF in dense stellar clusters such as the Arches cluster. The initial distributions of PSCs at various distances from the MC center are those of gravitationally unstable cores resulting from the gravo-turbulent fragmentation of the MC. As time evolves, there is a competition between the PSCs rates of coalescence and collapse. Whenever the local rate of collapse is larger than the rate of coalescence in a given mass bin, cores are collapsed into stars. With appropriate parameters, we find that the coalescence-collapse model reproduces very well all the observed characteristics of the Arches stellar cluster IMF; Namely, the slopes at high and low mass ends and the peculiar bump observed at ~5-6 M_sol. Our results suggest that today's IMF of the Arches cluster is very similar to the primordial one and is prior to the dynamical effects of mass segregation becoming importantComment: 5 pages, 2 figures, accepted to MNRAS Letter

    Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC

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    Heavy sterile neutrinos with masses below MWM_W can induce trilepton events at the 14 TeV LHC through purely leptonic WW decays of W±e±e±μνW^\pm \to e^\pm e^\pm \mu^\mp \nu and μ±μ±eν\mu^\pm \mu^\pm e^\mp \nu where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservability of the final state neutrino. This discrimination is done by exploiting a combined set of kinematic observables that differ between the Majorana vs. Dirac cases. We find that the MVA method can greatly enhance the discovering and discrimination limits in comparison with the CC method. For a 14-TeV pppp collider with integrated luminosity of 3000 fb1{\rm fb}^{-1}, sterile neutrinos can be found with 5σ\sigma significance if heavy-to-light neutrino mixings UNe2UNμ2106|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-6}, while the Majorana vs. Dirac type can be distinguished if UNe2UNμ2105|U_{Ne}|^2 \sim |U_{N\mu}|^2 \sim 10^{-5} or even UN2106|U_{N\ell}|^2\sim 10^{-6} if one of the mixing elements is at least an order of magnitude smaller than the other.Comment: 10 pages, 12 figure

    Search for Heavy Sterile Neutrinos in Trileptons at the LHC

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    We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of W±e±e±μνW^\pm \to e^\pm e^\pm \mu^\mp \nu and μ±μ±eν\mu^\pm \mu^\pm e^\mp \nu at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and discrimination limits. Two benchmark points with sterile neutrino mass mN=20m_N = 20 GeV and 50 GeV are tested. For an integrated luminosity of 3000 fb1{\rm fb}^{-1}, sterile neutrinos can be found with 5σ5 \sigma significance if heavy-to-light neutrino mixings UNe2UNμ2106|U_{Ne}|^2 \sim |U_{N\mu}|^2\sim 10^{-6}, while Majorana vs. Dirac discrimination can be reached if at least one of the mixings is of order 10510^{-5}.Comment: 4 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1703.0193

    Gas dynamics in Massive Dense Cores in Cygnus-X

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    We study the kinematic properties of dense gas surrounding massive protostars recognized by Bontemps et a. (2010) in a sample of five Massive Dense Cores in Cygnus-X. We investigate whether turbulent support plays a major role in stabilizing the core against fragmentation into Jeans-mass objects or alternatively, the observed kinematics could indicate a high level of dynamics. We present IRAM 30m single-dish (HCO+ and H13CO+) and IRAM PdBI high angular-resolution observations of dense gas tracers (H13CO+ and H13CN) to reveal the kinematics of molecular gas at scales from 0.03 to 0.1 pc. Radiative transfer modeling shows that H13CO+ is depleted within the envelopes of massive protostars and traces the bulk of material surrounding the protostars rather than their inner envelopes. H13CN shows a better correspondence with the peak of the continuum emission, possibly due to abundance anomalies and specific chemistry in the close vicinity of massive protostars. Analyzing the line-widths we show that the observed line-dispersion of H13CO+ at the scale of MDCs is smaller than expected from the quasi-static, turbulent-core model. At large-scales, global organized bulk motions are identified for 3 of the MDCs. At small-scales, several spectral components are identified in all MDCs showing filamentary structures and intrinsic velocity gradients towards the continuum peaks. The dynamics of these flows show diversity among the sample and we link this to the specific fragmentation properties of the MDCs. No clear evidence is found for a turbulence regulated, equilibrium scenario within the sample of MDCs. We propose a picture in which MDCs are not in equilibrium and their dynamics is governed by small-scale converging flows, which may initiate star-formation via their shears


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    As they home in on injured tissue, modulate the immune system and support tissue repairing, mesenchymal stem cells (MSCs) are considered a promising tool for many therapeutic applications. In vitro, MSCs have been shown to differentiate into multiple cell types mainly of the mesodermal, and more rarely of the endodermal and ectodermal lineage under appropriate conditions. In vivo, however, the beneficial effects mediated by MSCs are mainly attributed to paracrine factors they provide. MSCs are known to secrete large amounts of extracellular vesicles (EVs). EVs are thought to play an important role in intercellular communication, transferring proteins, nucleic acids and lipids to acceptor cells. To identify factors that contribute to the therapeutics roles of MSCs-derived EVs, we characterized the proteins enriched in them. MSCs-derived EVs were isolated from conditioned medium of cultured bone marrow–derived MSCs by ultra-centrifugation steps differentially isolating microvesicles (MVs) and exosomes. We performed LC-MS/MS-based proteomic analysis using reductive dimethylation labeling for quantitation of vesicular proteins against MSC whole cell lysate. In total, we identified 5207 proteins. 4695 and 4386 proteins were quantified in MVs and exosomes, respectively. We further analyzed the up-regulated proteins in both types of vesicles. Functional enrichment analysis was performed and hints at a high contribution of both MVs and exosomes to therapeutic applications of MSCs. EV proteins were linked to broad biological roles including extracellular matrix organization, cell migration, wound healing and hemostasis. Our findings strengthen the idea that MSCs-derived EVs may be a valuable replacement for MSCs in therapy.This study were conducted in the Proteomics Core Facility at WCM-Q which supported by the biomedical research program by Qatar Foundation, and partially funded by NPRP (No. 4-1267-1-194) grant from the Qatar National Research Fund

    Probing the Majorana neutrinos and their CP violation in decays of charged scalar mesons π,K,D,Ds,B,Bc\pi, K, D, D_s, B, B_c

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    Some of the outstanding questions of particle physics today concern the neutrino sector, in particular whether there are more neutrinos than those already known and whether they are Dirac or Majorana particles.There are different ways to explore these issues. In this article we describe neutrino-mediated decays of charged pseudoscalar mesons such as π±\pi^{\pm}, K±K^{\pm} and B±B^{\pm}, in scenarios where extra neutrinos are heavy and can be on their mass shell. We discuss semileptonic and leptonic decays of such kinds. We investigate possible ways of using these decays in order to distinguish between the Dirac and Majorana character of neutrinos. Further, we argue that there are significant possibilities of detecting CP violation in such decays when there are at least two almost degenerate Majorana neutrinos involved. This latter type of scenario fits well into the known neutrino minimal standard model (ν\nuMSM) which could simultaneously explain the Dark Matter and Baryon Asymmetry of the Universe.Comment: v3: 37 pages, 14 figures; minor typographical errors corrected; published in Symmetr