750 research outputs found

    Muonium spectrum beyond the nonrelativistic limit

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    A generalization of the Gell-Mann-Low theorem is applied to the antimuon-electron system. The bound state spectrum is extracted numerically. As a result, fine and hyperfine structure are reproduced correctly near the nonrelativistic limit (and for arbitrary masses). We compare the spectrum for the relativistic value alpha = 0.3 with corresponding calculations in light-front quantization.Comment: 6 pages, LaTeX, 2 figures, uses aipxfm.sty. Talk delivered at the XI Mexican Workshop on Particles and Fields, Tuxtla Gutierrez, Mexico, November 7-12, 2007; to be published in the proceeding

    Neutrino Flavor States and the Quantum Theory of Neutrino Oscillations

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    The standard theory of neutrino oscillations is reviewed, highlighting the main assumptions: the definition of the flavor states, the equal-momentum assumption and the time = distance assumption. It is shown that the standard flavor states are correct approximations of the states that describe neutrinos in oscillation experiments. The equal-momentum assumption is shown to be unnecessary for the derivation of the oscillation probability. The time = distance assumption derives from the wave-packet character of the propagating neutrinos. We present a simple quantum-mechanical wave-packet model which allows us to describe the coherence and localization of neutrino oscillations.Comment: 16 pages; talk presented at the XI Mexican Workshop on Particles and Fields, 7-12 November 2007, Tuxtla Gutierrez, Chiapas, Mexic

    Coherent nu-N scattering and the search for physics beyond the standard model

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    We focus in future proposals to measure coherent neutrino-nuclei scattering and we show that such kind of experiments are very sensitive to nonstandard neutrino interactions with quarks. First in a model independent parametrization and then we focused in particular models such as leptoquarks and models with extra neutral gauge bosons and with R-parity breaking interactions. We show that in all these three different types of new physics it is possible to obtain competitive bounds to those of future collider experiments. For the particular case of leptoquarks we found that the expected sensitivity to the coupling and mass for most of the future experimental setups is quite better than the current constraints.Comment: 6 pages, 1 Figure, Talk given at 11th Mexican Workshop on Particles and Fields 2007, Tuxtla Gutierrez, Mexico, 7-12 Nov 200

    Dinámica sociopolítica del conflicto y la violencia en territorio mapuche. Particularidades históricas de un nuevo ciclo en las relaciones contenciosas

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    From an empirical and historical approach, this research looks at the course of contemporarycon-tention in Mapuche territory. Drawing both upon secondary sources and first-hand testimonies of mobilized Mapuche communities in Arauco Province, this paper reveals innovations and significant continuities within the current cycle of contentious relations among the Chilean state, the Mapuche movement and the big forest capital. Paying particular attention to the socio-political context, this study analyzes the ongoing dynamic transformation, on one hand, of the suppression of Mapuche protests, and on the other hand, of the modalities of collective action itself and its discursive foundations. This paper addresses a new cycle of contention marked by the rise of violence, unrest, and the closure of institutional and political channels. The authors argue that the explicative sources of contention and its by-product violence mainly stems from the very interaction among the actors, the frames and repertories of the protest, and the institutional political scenario itself.Esta investigación revisa histórica y empíricamente el curso de la contienda política contemporánea en territorio mapuche. Desde fuentes secundarias, como también desde el mismo relato de comunidades movilizadas en la provincia de Arauco, se identifican ciertas continuidades y novedades en el actual ciclo de relaciones contenciosas entre el movimiento mapuche, el Estado chileno y el gran capital forestal. Con especial atención en el contexto sociopolítico, se estudia cómo se han transformado dinámicamente, desde un lado, las estrategias de supresión de la protesta mapuche y, desde el otro, las modalidades de la propia acción colectiva y sus fundamentos discursivos. Este estudio describe un nuevo ciclo de contienda marcado por el incremento de la conflictividad, la violencia y el cierre de los canales político-institucionales. Esta investigación plantea que las fuentes explicativas de la contienda y la violencia derivada estarían principalmente en la propia interacción entre los actores, entre sus marcos y repertorios de protesta, y el propio escenario político institucional

    Probing new physics with coherent neutrino scattering off nuclei

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    The possibility off measuring for the first time neutrino-nuclei coherent scattering has been recently discussed by several experimental collaborations. It is shown that such a measurement may be very sensitive to non-standard interactions of neutrinos with quarks and might set better constraints than those coming from future neutrino factory experiments. We also comment on other types of new physics tests, such as extra heavy neutral gauge bosons, where the sensitivity to some models is slightly better than the Tevatron constraint and, therefore, could give complementary bounds.Comment: 15 pages, 4 figures Discussion about Z prime corrected and extended. Final version to be published in JHE

    Constraining a bulk viscous matter-dominated cosmological model using SNe Ia, CMB and LSS

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    We present and constrain a cosmological model which component is a pressureless fluid with bulk viscosity as an explanation for the present accelerated expansion of the universe. We study the particular model of a constant bulk viscosity coefficient \zeta_m. The possible values of \zeta_m are constrained using the cosmological tests of SNe Ia Gold 2006 sample, the CMB shift parameter R from the three-year WMAP observations, the Baryon Acoustic Oscillation (BAO) peak A from the Sloan Digital Sky Survey (SDSS) and the Second Law of Thermodynamics (SLT). It was found that this model is in agreement with the SLT using only the SNe Ia test. However when the model is submitted to the three cosmological tests together (SNe+CMB+BAO) the results are: 1.- the model violates the SLT, 2.- predicts a value of H_0 \approx 53 km sec^{-1} Mpc^{-1} for the Hubble constant, and 3.- we obtain a bad fit to data with a \chi^2_{min} \approx 400 (\chi^2_{d.o.f.} \approx 2.2). These results indicate that this model is ruled out by the observations.Comment: 4 pages, 1 figure. Work presented in the XI Mexican Workshop on Particles and Fields, Tuxtla Gutierrez, Mexico, nov 7-12, 2007. Submitted to AIP Conference Proceedings of this conferenc

    Geometrical constraints on dark energy models

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    This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic oscillations test. An historical overview of Cosmology is followed by some generalities on FRW spacetimes (the best large-scale description of the Universe), and then the test themselves are discussed. A convenient section on statistical inference is included as well.Comment: 28 pages, 15 pages, lecture notes prepared for the ``Advanced Summer School in Physics 2007" organized by Cinvestav (Mexico DF

    Proton to pion ratio at RHIC from dynamical quark recombination

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    We propose an scenario to study, from a dynamical point of view, the thermal recombination of quarks in the midsts of a relativistic heavy-ion collision. We coin the term dynamical quark recombination to refer to the process of quark-antiquark and three-quark clustering, to form mesons and baryons, respectively, as a function of energy density. Using the string-flip model we show that the probabilities to form such clusters differ. We apply these ideas to the calculation of the proton and pion spectra in a Bjorken-like scenario that incorporates the evolution of these probabilities with proper time and compute the proton to pion ratio, comparing to recent RHIC data at the highest energy. We show that for a standard choice of parameters, this ratio reaches one, though the maximum is very sensitive to the initial evolution proper time.Comment: To appear in the proceedings of the XI Mexican Workshop on Particles and Fields, Tuxtla Gutierrez Chiapas, Mexico, 7-12 Nov. 200

    Trayectoria tecnológica y uso del agua en la agricultura argentina bajo riego

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    Three elements which influence the dynamic in technologicalselection of agricultural irrigation systems were studied. Inthe first place, the level of scarcity of water resources; theavailability of water depends both on climate factors that affectsuperficial and underground aquifers, and on conditions ofdeficient supply through public networks. One of the paths toface this scarcity is adopting drip irrigation, which allows amore efficient use of water. In the second place, productiverestructuring of oases irrigated to the west of the country,induced by habits of consumption of healthy and hedonicfoods; the technological package associated with new cropsincludes drip irrigation, which is part of innovating productiontechniques that have a greater capital intensity and betterproductivity by the workforce as common denominator. Finally,the size of the farms; the presence of indivisibilities in irrigationequipment makes their cost per hectare decrease as the surfaceirrigated increases.Se estudiaron tres elementos que influyen en la din√°mica de laelecci√≥n tecnol√≥gica de los sistemas de riego agr√≠cola. En primerlugar, el nivel de escasez de recursos h√≠dricos; la disponibilidadde agua depende tanto de factores clim√°ticos que afectan los acu√≠ferossuperficiales y subterr√°neos como de condiciones deficientesde suministro en las redes p√ļblicas. Uno de los caminos parahacer frente a la escasez es la adopci√≥n de riego por goteo, el cualpermite hacer un uso m√°s eficiente del agua. En segundo lugar,la reestructuraci√≥n productiva de los oasis irrigados del oeste delpa√≠s, inducida por h√°bitos de consumo de alimentos saludables yhed√≥nicos; el paquete tecnol√≥gico asociado a los nuevos cultivosincluye al riego por goteo, el cual forma parte de t√©cnicas deproducci√≥n innovadoras que tienen como denominador com√ļnmayor intensidad de capital y mayor productividad de la manode obra. Finalmente el tama√Īo de las fincas; la presencia de indivisibilidadesen los equipos de riego hace que disminuya su costopor hect√°rea a medida que aumenta la superficie regada

    Electrochemical Properties of Al2O3-Fe/Si Composites Prepared by High-Energy Mechanical Milling

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    open accessThe growing demand in the manufacture of advanced materials with desired and unique properties (e.g. high mechanical strength, durability, good corrosion resistance and low cost of maintenance/replacing) is one of reasons to motivate the researchers to pay special attention in Ceramics as high performance materials for industrial applications. This is because conventional materials cannot meet the engineering requirements during their service that is why the need for advanced ceramic materials to achieve these industrial requirements. In the present work a study was made on Al2O3-matrix ceramic composites reinforced with 2%wt. or 5% wt. of Fe/Si particulates that were produced using a mechanical ball milling at high-energy condition. The electrochemical behavior of these ceramics was investigated by anodic polarization and Electrochemical Impedance Spectroscopy (EIS) measurements in a solution containing 0.5N NaCl, whereas the morphology and microstructural features were examined by optical or Scanning Electron Microscopy (SEM)
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