14 research outputs found

    Surface terms, Asymptotics and Thermodynamics of the Holst Action

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    We consider a first order formalism for general relativity derived from the Holst action. This action is obtained from the standard Palatini-Hilbert form by adding a topological-like term and can be taken as the starting point for loop quantum gravity and spin foam models. The equations of motion derived from the Holst action are, nevertheless, the same as in the Palatini formulation. Here we study the form of the surface terms of the action for general boundaries as well as the symplectic current in the covariant formulation of the theory. Furthermore, we analyze the behavior of the surface terms in asymptotically flat space-times. We show that the contribution to the symplectic structure from the Holst term vanishes and one obtains the same asymptotic expressions as in the Palatini action. It then follows that the asymptotic Poincare symmetries and conserved quantities such as energy, linear momentum and relativistic angular momentum found here are equivalent to those obtained from the standard Arnowitt, Deser and Misner formalism. Finally, we consider the Euclidean approach to black hole thermodynamics and show that the on-shell Holst action, when evaluated on some static solutions containing horizons, yields the standard thermodynamical relations.Comment: 16 page

    Barbero-Immirzi parameter, manifold invariants and Euclidean path integrals

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    The Barbero-Immirzi parameter Îł\gamma appears in the \emph{real} connection formulation of gravity in terms of the Ashtekar variables, and gives rise to a one-parameter quantization ambiguity in Loop Quantum Gravity. In this paper we investigate the conditions under which Îł\gamma will have physical effects in Euclidean Quantum Gravity. This is done by constructing a well-defined Euclidean path integral for the Holst action with non-zero cosmological constant on a manifold with boundary. We find that two general conditions must be satisfied by the spacetime manifold in order for the Holst action and its surface integral to be non-zero: (i) the metric has to be non-diagonalizable; (ii) the Pontryagin number of the manifold has to be non-zero. The latter is a strong topological condition, and rules out many of the known solutions to the Einstein field equations. This result leads us to evaluate the on-shell first-order Holst action and corresponding Euclidean partition function on the Taub-NUT-ADS solution. We find that Îł\gamma shows up as a finite rotation of the on-shell partition function which corresponds to shifts in the energy and entropy of the NUT charge. In an appendix we also evaluate the Holst action on the Taub-NUT and Taub-bolt solutions in flat spacetime and find that in that case as well Îł\gamma shows up in the energy and entropy of the NUT and bolt charges. We also present an example whereby the Euler characteristic of the manifold has a non-trivial effect on black-hole mergers.Comment: 18 pages; v2: references added; to appear in Classical and Quantum Gravity; v3: typos corrected; minor revisions to match published versio

    Differential effects of methyl jasmonate on growth and division of etiolated zucchini cotyledons

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    Measurements of the jet energy calibration and transverse momentum resolution in CMS are presented, performed with a data sample collected in proton-proton collisions at a centre-of-mass energy of 7TeV, corresponding to an integrated luminosity of 36pb-1. The transverse momentum balance in dijet and Îł/Z+jets events is used to measure the jet energy response in the CMS detector, as well as the transverse momentum resolution. The results are presented for three different methods to reconstruct jets: a calorimeter-based approach, the "Jet-Plus-Track" approach, which improves the measurement of calorimeter jets by exploiting the associated tracks, and the "Particle Flow" approach, which attempts to reconstruct individually each particle in the event, prior to the jet clustering, based on information from all relevant subdetectors

    Electroweak parameters of the z0 resonance and the standard model

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    Contains fulltext : 124399.pdf (publisher's version ) (Open Access

    Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

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    Contains fulltext : 121524.pdf (preprint version ) (Open Access

    Electroweak parameters of the Z0^0 resonance and the standard model

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    Media temporalities of the elderly : evolutions in stability This article shows the context of analysis and the first results of a research on media temporalities of the elderly. Several works have finely analysed the diversity of the media practices and studied meanings of media uses. I wish to continue these analyses by insisting on the evolutionary and dynamic aspect of the practices and temporalities of users having expanded, enhanced, so called "interactive" radio and especially television programming. A priori, the elderly, upon retirement, have a "full-time free time". Their media practices seem strongly influenced by their first experiments ; the appropriation of the various peripheral accessories which gradually came with the media, to the latest digital ones, seems to reinforce their habits of watching television. Their representations and relations with times and media are very far away from the image of television like omnipresent media or "devourer of time". Rather, their media practices are to be understood like a temporality of the occupation, according to the expression of Gerard DerĂšze, characterized by interest and utility. A particular glance at the users who do not carry out a systematic selection of the programs, accepting the unforeseen, highlights an approach of media and time that allow "useful encounter" which I would qualify in a first stage by : "chance and encounter" and "random and the following". The few points presented here make me assume that the global relation of the autonomous elderly persons to the media can evolve when confronted to their new temporal framework and the new program offer, whereas their representations and use of the media remain quite stable

    Electroweak parameters of the Z0^0 resonance and the standard model

    No full text
    Media temporalities of the elderly : evolutions in stability This article shows the context of analysis and the first results of a research on media temporalities of the elderly. Several works have finely analysed the diversity of the media practices and studied meanings of media uses. I wish to continue these analyses by insisting on the evolutionary and dynamic aspect of the practices and temporalities of users having expanded, enhanced, so called "interactive" radio and especially television programming. A priori, the elderly, upon retirement, have a "full-time free time". Their media practices seem strongly influenced by their first experiments ; the appropriation of the various peripheral accessories which gradually came with the media, to the latest digital ones, seems to reinforce their habits of watching television. Their representations and relations with times and media are very far away from the image of television like omnipresent media or "devourer of time". Rather, their media practices are to be understood like a temporality of the occupation, according to the expression of Gerard DerĂšze, characterized by interest and utility. A particular glance at the users who do not carry out a systematic selection of the programs, accepting the unforeseen, highlights an approach of media and time that allow "useful encounter" which I would qualify in a first stage by : "chance and encounter" and "random and the following". The few points presented here make me assume that the global relation of the autonomous elderly persons to the media can evolve when confronted to their new temporal framework and the new program offer, whereas their representations and use of the media remain quite stable

    The ATLAS Experiment at the CERN Large Hadron Collider

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    The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented

    Precision Electroweak Measurements on the Z resonance.

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    We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron–positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLD experiment using a polarised beam at SLC. The measurements include cross-sections, forward–backward asymmetries and polarised asymmetries. The mass and width of the Z boson, mZ and ΓZ, and its couplings to fermions, for example the ρ parameter and the effective electroweak mixing angle for leptons, are precisely measured: The number of light neutrino species is determined to be 2.9840±0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward–backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, , and the mass of the W boson, . These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of mt and mW, the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than at 95% confidence level
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