756 research outputs found

    Finite-Volume QED Corrections to Decay Amplitudes in Lattice QCD

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    We demonstrate that the leading and next-to-leading finite-volume effects in the evaluation of leptonic decay widths of pseudoscalar mesons at O(α)O(\alpha) are universal, i.e. they are independent of the structure of the meson. This is analogous to a similar result for the spectrum but with some fundamental differences, most notably the presence of infrared divergences in decay amplitudes. The leading non-universal, structure-dependent terms are of O(1/L2)O(1/L^2) (compared to the O(1/L3)O(1/L^3) leading non-universal corrections in the spectrum). We calculate the universal finite-volume effects, which requires an extension of previously developed techniques to include a dependence on an external three-momentum (in our case, the momentum of the final state lepton). The result can be included in the strategy proposed in Ref.\,\cite{Carrasco:2015xwa} for using lattice simulations to compute the decay widths at O(α)O(\alpha), with the remaining finite-volume effects starting at order O(1/L2)O(1/L^2). The methods developed in this paper can be generalised to other decay processes, most notably to semileptonic decays, and hence open the possibility of a new era in precision flavour physics

    Electromagnetic corrections to leptonic decay rates of charged pseudoscalar mesons: finite-volume effects

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    In Carrasco et al. we have recently proposed a method to calculate O(e2)O(e^2) electromagnetic corrections to leptonic decay widths of pseudoscalar mesons. The method is based on the observation that the infrared divergent contributions (that appear at intermediate stages of the calculation and that cancel in physical quantities thanks to the Bloch-Nordsieck mechanism) are universal, i.e. depend on the charge and the mass of the meson but not on its internal structure. In this talk we perform a detailed analysis of the finite-volume effects associated with our method. In particular we show that also the leading 1/L1/L finite-volume effects are universal and perform an analytical calculation of the finite-volume leptonic decay rate for a point-like meson

    The Dependence of the Field Decay on the Powering History of the LHC Superconducting Dipole Magnets

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    The decay of the allowed multipoles in the Large Hadron Collider (LHC) dipoles is expected to perturb the beam stability during the particle injection. The decay amplitude is largely affected by the powering history of the magnet and is particularly dependent on the pre-cycle flat-top current and duration as well as the pre-injection preparation duration. With possible prospects of having different genres of cycles during the LHC operation, the powering history effect must be taken into account in the Field Description Model for the LHC and must hence be corrected during machine operation. This paper presents the results of the modelling of this phenomenon

    Cambridge as a place in economics

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    Cambridge as a geographical reference often crops up in the characterisation of the economic theories and approaches that developed in Cambridge (UK) between the 1920s and the 1960s with the contribution of economists who did not always share the same interests, background or attitudes, but who all lived and worked – for considerable periods of time – in that particular corner of the world. In order to reconstruct the Cambridge of those years and explore the space it represented for economics we have selected a group of economists and a span of time – essentially between the two wars, with a few encroachments in the years following on the death of Keynes. Cambridge was not only a place, but also a play of magnetic forces, drawing together and driving apart, where ideas emerged from an environment formed through intense human and professional relations, a well defined cultural tradition and a way of its own of organising work and study. We present the dramatis personae and the background to their actions, and consider the characteristics of intellectual and personal communication on the basis of which we are led to define the Cambridge economists examined more as a `group' than a school

    First lattice calculation of the QED corrections to leptonic decay rates

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    The leading-order electromagnetic and strong isospin-breaking corrections to the ratio of Kμ2K_{\mu 2} and πμ2\pi_{\mu 2} decay rates are evaluated for the first time on the lattice, following a method recently proposed. The lattice results are obtained using the gauge ensembles produced by the European Twisted Mass Collaboration with Nf=2+1+1N_f = 2 + 1 + 1 dynamical quarks. Systematics effects are evaluated and the impact of the quenched QED approximation is estimated. Our result for the correction to the tree-level Kμ2/πμ2K_{\mu 2} / \pi_{\mu 2} decay ratio is −1.22 (16)%-1.22\,(16) \% to be compared to the estimate −1.12 (21)%-1.12\,(21) \% based on Chiral Perturbation Theory and adopted by the Particle Data Group.Comment: 5 pages, 6 figures; extended supplemental material with 1 table and 1 figure, results unchange

    Left ventricular systolic function evaluated by strain echocardiography and relationship with mortality in patients with severe sepsis or septic shock. a systematic review and meta-analysis

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    Sepsis-induced myocardial dysfunction is associated with poor outcomes, but traditional measurements of systolic function such as left ventricular ejection fraction (LVEF) do not directly correlate with prognosis. Global longitudinal strain (GLS) utilizing speckle-tracking echocardiography (STE) could be a better marker of intrinsic left ventricular (LV) function, reflecting myocardial deformation rather than displacement and volume changes. We sought to investigate the prognostic value of GLS in patients with sepsis and/or septic shock

    Light-meson leptonic decay rates in lattice QCD+QED

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    The leading electromagnetic (e.m.) and strong isospin-breaking corrections to the π+→μ+ν[γ]\pi^+ \to \mu^+ \nu[\gamma] and K+→μ+ν[γ]K^+ \to \mu^+ \nu[\gamma] leptonic decay rates are evaluated for the first time on the lattice. The results are obtained using gauge ensembles produced by the European Twisted Mass Collaboration with Nf=2+1+1N_f = 2 + 1 + 1 dynamical quarks. The relative leading-order e.m.~and strong isospin-breaking corrections to the decay rates are 1.53(19)\% for πμ2\pi_{\mu 2} decays and 0.24(10)\% for Kμ2K_{\mu 2} decays. Using the experimental values of the πμ2\pi_{\mu 2} and Kμ2K_{\mu 2} decay rates and updated lattice QCD results for the pion and kaon decay constants in isosymmetric QCD, we find that the Cabibbo-Kobayashi-Maskawa matrix element ∣Vus∣=0.22538(46) | V_{us}| = 0.22538(46), reducing by a factor of about 1.81.8 the corresponding uncertainty in the Particle Data Group review. Our calculation of ∣Vus∣|V_{us}| allows also an accurate determination of the first-row CKM unitarity relation ∣Vud∣2+∣Vus∣2+∣Vub∣2=0.99988(46)| V_{ud}|^2 + | V_{us}|^2 + | V_{ub}|^2 = 0.99988(46). Theoretical developments in this paper include a detailed discussion of how QCD can be defined in the full QCD+QED theory and an improved renormalisation procedure in which the bare lattice operators are renormalised non-perturbatively into the (modified) Regularization Independent Momentum subtraction scheme and subsequently matched perturbatively at O(αemαs(MW))O(\alpha_{em}\alpha_s(M_W)) into the W-regularisation scheme appropriate for these calculations.Comment: 63 pages, 10 figures and 2 tables. Version matches the published pape
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