Search results for "Low energy"
showing 10 items of 147 documents
Response to “Comment on ‘Comparison and uncertainty evaluation of different calibration protocols and ionization chambers for low-energy surface brac…
2016
Low-energy epicardial pacing in children: the benefit of autocapture.
1999
Abstract Background . Permanent cardiac pacing in children results commonly in augmented energy consumption because of the high pacing rates and the ample stimulation safety margin applied in children. Cardiovascular anatomy and limited venous access sometimes preclude the otherwise preferred endocardial approach. In this multicenter patient series, we studied the feasibility, safety, and energy saving obtained by a combination of steroid-eluting epicardial leads with autocapture devices capable of ongoing adjustment of the stimulation output to the prevailing threshold. Methods . Autocapture devices (Pacesetter Microny SR+ and Regency SR+; Pacesetter, Solna, Sweden) and steroid-eluting epi…
Towards a consistent estimate of the chiral low-energy constants
2006
Guided by the large-N_C limit of QCD, we construct the most general chiral resonance Lagrangian that can generate chiral low-energy constants up to O(p^6). By integrating out the resonance fields, the low-energy constants are parametrized in terms of resonance masses and couplings. Information on those couplings and on the low-energy constants can be extracted by analysing QCD Green functions of currents both for large and small momenta. The chiral resonance theory generates Green functions that interpolate between QCD and chiral perturbation theory. As specific examples we consider the VAP and SPP Green functions.
Rare decays of neutral kaons
1998
This report summarises results on rare decays of neutral kaons. Three different classes of decays are discussed. Most of the examples were taken from results of the NA31 experiment. Therefore, the experiment is described in the first chapter. Subject of the second chapter are decays allowing to measure the CP-violation (i.e. KL → π0 e+e−) and some related decays (i.e. KL → γγe+e− as the worst background process to KL → π0 e+e−). In the third chapter searches for decays which are forbidden or highly suppressed in the Standard model are discussed. The forth chapter describes the measurements of decays allowing to test low energy QCD. The last chapter lists the prospects for the future of stud…
Highlights and perspectives of the Mainz microtron MAMI
2003
Abstract An overview of the idea behind the physics of the MAMI laboratory and its realization is given. The introduction attempts to show the importance of the physics of hadrons in the general realm and emphasizes the low energy domain as the key to study Quantum Chromo Dynamics (QCD). Next some highlights of results at MAMI are presented illustrating this idea. New significant experiments to proceed with this approach to QCD are discussed. This is followed by a description of the upgrade of the existing MAMI B with 0.885 GeV to MAMI C with 1.5 GeV and of the new experimental equipment making the new experiments possible.
Light meson physics from maximally twisted mass lattice QCD
2009
40 pages, 5 figures, 8 tables, 3 appendix.-- PACS: 11.15.Ha; 12.38.Gc; 12.39.Fe
Form factors of radiative pion decays in nonlocal chiral quark models
2012
We study the radiative pion decay π +→e +ν eγ within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F V(q2) and the slope of the axial-vector form factor F A(q2) at threshold. Our results are compared with available experimental information and with the predictions given by the Nambu-Jona-Lasinio model. In addition we calculate the low energy constants δ 5 and δ 6, comparing our results with the values obtained in chiral perturbation theory.
Polarized structure functions in a constituent quark scenario
1998
Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. Using unpolarized data to fix the parameters we achieve good agreement with the polarization experiments for the proton, while not so for the neutron. By relaxing our assumptions for the sea distributions, we define new quark functions for the polarized case, which reproduce well the proton data and are in better agreement with the neutron data. When our results are compared with similar calculations using non-composite constituent quarks the ac…
Low-energy particle physics and chiral extrapolations
2012
In this review I discuss the role of chiral extrapolations for the determination of several phenomenologically relevant quantities, including light quark masses, meson decay constants and the axial charge of the nucleon. In particular, I investigate whether chiral extrapolations are sufficiently controlled in order to rightfully claim the accuracy which is quoted in recent compilations of these quantities. While this is the case for the masses of the light quarks and the ratio fK/fpi of decay constants, small inconsistencies in the chiral and continuum behaviour of individual decay constants fK and fpi, as well as the hadronic radii r0, r1 remain and must be clarified. In the case of the nu…
Quark degrees of freedom in hadronic systems
2000
Quantum Chromodynamics (QCD) is the theory of the strong interactions. We review descriptions of hadronic systems motivated by QCD, analyzing the recent controversy between gluonic and bosonic degrees of freedom under the prism of the Cheshire Cat Principle. Our analysis leads to an optimal scheme to study hadronic properties. We proceed to extend this low energy descriptions to the deep inelastic regime.