225 research outputs found

    About Bianchi I with VSL

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    In this paper we study how to attack, through different techniques, a perfect fluid Bianchi I model with variable G,c and Lambda, but taking into account the effects of a cc-variable into the curvature tensor. We study the model under the assumption,div(T)=0. These tactics are: Lie groups method (LM), imposing a particular symmetry, self-similarity (SS), matter collineations (MC) and kinematical self-similarity (KSS). We compare both tactics since they are quite similar (symmetry principles). We arrive to the conclusion that the LM is too restrictive and brings us to get only the flat FRW solution. The SS, MC and KSS approaches bring us to obtain all the quantities depending on \int c(t)dt. Therefore, in order to study their behavior we impose some physical restrictions like for example the condition q<0 (accelerating universe). In this way we find that cc is a growing time function and Lambda is a decreasing time function whose sing depends on the equation of state, w, while the exponents of the scale factor must satisfy the conditions ∑i=13αi=1\sum_{i=1}^{3}\alpha_{i}=1 and ∑i=13αi2<1,\sum_{i=1}^{3}\alpha_{i}^{2}<1, ∀ω\forall\omega, i.e. for all equation of state,, relaxing in this way the Kasner conditions. The behavior of GG depends on two parameters, the equation of state ω\omega and Ï”,\epsilon, a parameter that controls the behavior of c(t),c(t), therefore GG may be growing or decreasing.We also show that through the Lie method, there is no difference between to study the field equations under the assumption of a c−c-var affecting to the curvature tensor which the other one where it is not considered such effects.Nevertheless, it is essential to consider such effects in the cases studied under the SS, MC, and KSS hypotheses.Comment: 29 pages, Revtex4, Accepted for publication in Astrophysics & Space Scienc

    Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab

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    We present measurements of the differential cross section and Lambda recoil polarization for the gamma p to K+ Lambda reaction made using the CLAS detector at Jefferson Lab. These measurements cover the center-of-mass energy range from 1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles. Independent analyses were performed using the K+ p pi- and K+ p (missing pi -) final-state topologies; results from these analyses were found to exhibit good agreement. These differential cross section measurements show excellent agreement with previous CLAS and LEPS results and offer increased precision and a 300 MeV increase in energy coverage. The recoil polarization data agree well with previous results and offer a large increase in precision and a 500 MeV extension in energy range. The increased center-of-mass energy range that these data represent will allow for independent study of non-resonant K+ Lambda photoproduction mechanisms at all production angles.Comment: 22 pages, 16 figure

    First measurement of direct f0(980)f_0(980) photoproduction on the proton

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    We report on the results of the first measurement of exclusive f0(980)f_0(980) meson photoproduction on protons for EÎł=3.0−3.8E_\gamma=3.0 - 3.8 GeV and −t=0.4−1.0-t = 0.4-1.0 GeV2^2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The resonance was detected via its decay in the π+π−\pi^+ \pi^- channel by performing a partial wave analysis of the reaction Îłp→pπ+π−\gamma p \to p \pi^+ \pi^-. Clear evidence of the f0(980)f_0(980) meson was found in the interference between PP and SS waves at Mπ+π−∌1M_{\pi^+ \pi^-}\sim 1 GeV. The SS-wave differential cross section integrated in the mass range of the f0(980)f_0(980) was found to be a factor of 50 smaller than the cross section for the ρ\rho meson. This is the first time the f0(980)f_0(980) meson has been measured in a photoproduction experiment

    Bianchi II with time varying constants. Self-similar approach

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    We study a perfect fluid Bianchi II models with time varying constants under the self-similarity approach. In the first of the studied model, we consider that only vary GG and Λ.\Lambda. The obtained solution is more general that the obtained one for the classical solution since it is valid for an equation of state ω∈(−1,∞)\omega\in(-1,\infty) while in the classical solution ω∈(−1/3,1).\omega\in(-1/3,1) . Taking into account the current observations, we conclude that GG must be a growing time function while Λ\Lambda is a positive decreasing function. In the second of the studied models we consider a variable speed of light (VSL). We obtain a similar solution as in the first model arriving to the conclusions that cc must be a growing time function if Λ\Lambda is a positive decreasing function.Comment: 10 pages. RevTeX

    Updated Nucleosynthesis Constraints on Unstable Relic Particles

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    We revisit the upper limits on the abundance of unstable massive relic particles provided by the success of Big-Bang Nucleosynthesis calculations. We use the cosmic microwave background data to constrain the baryon-to-photon ratio, and incorporate an extensively updated compilation of cross sections into a new calculation of the network of reactions induced by electromagnetic showers that create and destroy the light elements deuterium, he3, he4, li6 and li7. We derive analytic approximations that complement and check the full numerical calculations. Considerations of the abundances of he4 and li6 exclude exceptional regions of parameter space that would otherwise have been permitted by deuterium alone. We illustrate our results by applying them to massive gravitinos. If they weigh ~100 GeV, their primordial abundance should have been below about 10^{-13} of the total entropy. This would imply an upper limit on the reheating temperature of a few times 10^7 GeV, which could be a potential difficulty for some models of inflation. We discuss possible ways of evading this problem.Comment: 40 pages LaTeX, 18 eps figure

    Subcutaneous abatacept in patients with polyarticular-course juvenile idiopathic arthritis : results from a phase III open-label study

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    OBJECTIVE : To investigate the pharmacokinetics, effectiveness, and safety of subcutaneous (SC) abatacept treatment over 24 months in patients with polyarticular‐course juvenile idiopathic arthritis (JIA). METHODS: In this phase III, open‐label, international, multicenter, single‐arm study, patients with polyarticular JIA (cohort 1, ages 6–17 years and cohort 2, ages 2–5 years) in whom treatment with ≄1 disease‐modifying antirheumatic drug was unsuccessful received weight‐tiered SC abatacept weekly: 10 to <25 kg (50 mg), 25 to <50 kg (87.5 mg), ≄50 kg (125 mg). Patients who had met the JIA–American College of Rheumatology 30% improvement criteria (achieved a JIA‐ACR 30 response) at month 4 were given the option to continue SC abatacept to month 24. The primary end point was the abatacept steady‐state serum trough concentration (Cminss) in cohort 1 at month 4. Other outcome measures included JIA‐ACR 30, 50, 70, 90, 100, and inactive disease status, the median Juvenile Arthritis Disease Activity Score in 71 joints using the C‐reactive protein level (JADAS‐71–CRP) over time, safety, and immunogenicity. RESULTS : The median abatacept Cminss at month 4 (primary end point) and at month 24 was above the target therapeutic exposure (10 ÎŒg/ml) in both cohorts. The percentage of patients who had achieved JIA‐ACR 30, 50, 70, 90, or 100 responses or had inactive disease responses at month 4 (intent‐to‐treat population) was 83.2%, 72.8%, 52.6%, 28.3%, 14.5%, and 30.1%, respectively, in cohort 1 (n = 173) and 89.1%, 84.8%, 73.9%, 58.7%, 41.3%, and 50.0%, respectively, in cohort 2 (n = 46); the responses were maintained to month 24. The median (interquartile range) JADAS‐71–CRP improved from baseline to month 4: cohort 1, from 21.0 (13.5, 30.3) to 4.6 (2.1, 9.4); cohort 2, from 18.1 (14.0, 23.1) to 2.1 (0.3, 4.4). Improvements were sustained to month 24, at which time 27 of 173 patients (cohort 1) and 11 of 22 patients (cohort 2) had achieved JADAS‐71–CRP remission. No unexpected adverse events were reported; 4 of 172 patients (2.3%) in cohort 1 and 4 of 46 (8.7%) in cohort 2 developed anti‐abatacept antibodies, with no clinical effects. CONCLUSION : Weight‐stratified SC abatacept yielded target therapeutic exposures across age and weight groups, was well tolerated, and improved polyarticular JIA symptoms over 24 months.Results From a Phase III Open‐Label StudyWriting assistance was funded by Bristol‐Myers Squibb.https://onlinelibrary.wiley.com/journal/23265205am2018Internal Medicin

    Partial wave analysis of the reaction gamma p -> p omega$ and the search for nucleon resonances

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    An event-based partial wave analysis (PWA) of the reaction gamma p -> p omega has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> pi+ pi - pi0. The data confirm the dominance of the t-channel pi0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as well as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2(+) state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive

    Paleobiology of titanosaurs: reproduction, development, histology, pneumaticity, locomotion and neuroanatomy from the South American fossil record

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    Fil: García, Rodolfo A.. Instituto de Investigación en Paleobiología y Geología. Museo Provincial Carlos Ameghino. Cipolletti; ArgentinaFil: Salgado, Leonardo. Instituto de Investigación en Paleobiología y Geología. General Roca. Río Negro; ArgentinaFil: Fernåndez, Mariela. Inibioma-Centro Regional Universitario Bariloche. Bariloche. Río Negro; ArgentinaFil: Cerda, Ignacio A.. Instituto de Investigación en Paleobiología y Geología. Museo Provincial Carlos Ameghino. Cipolletti; ArgentinaFil: Carabajal, Ariana Paulina. Museo Carmen Funes. Plaza Huincul. Neuquén; ArgentinaFil: Otero, Alejandro. Museo de La Plata. Universidad Nacional de La Plata; ArgentinaFil: Coria, Rodolfo A.. Instituto de Paleobiología y Geología. Universidad Nacional de Río Negro. Neuquén; ArgentinaFil: Fiorelli, Lucas E.. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica. Anillaco. La Rioja; Argentin
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