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Search Results: 1 - 10 of 462247 matches for " A. Bernstein "
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Characteristics of nonallergic vasomotor rhinitis
Jonathan A Bernstein
World Allergy Organization Journal , 2009, DOI: 10.1097/wox.0b013e3181a8e389
Abstract:
Opening Remarks at Chiral Dynamics 2006:Experimental Tests of Chiral Symmetry Breaking
Bernstein, A. M.
High Energy Physics - Phenomenology , 2007,
Abstract: A physical introduction to the basics of chiral dynamics is presented. Emphasis is placed on experimental tests which have generally demonstrated a strong confirmation of the predictions of chiral perturbation theory, a low energy effective field theory of QCD. Special attention is paid to a few cases where discrepancies exist, requiring further work. Some desirable future tests are also recommended.
Pions: Experimental Tests of Chiral Symmetry Breaking
Bernstein, A. M.
High Energy Physics - Phenomenology , 2013,
Abstract: Based on the spontaneous breaking of chiral symmetry, chiral perturbation theory (ChPT) is believed to approximate confinement scale QCD. Dedicated and increasingly accurate experiments and improving lattice calculations are confirming this belief, and we are entering a new era in which we can test confinement scale QCD in some well chosen reactions. This is demonstrated with an overview of low energy experimental tests of ChPT predictions of $\pi\pi$ scattering, pion properties, $\pi$N scattering and electromagnetic pion production. These predictions have been shown to be consistent with QCD in the meson sector by increasingly accurate lattice calculations. At present there is good agreement between experiment and ChPT calculations, including the $\pi\pi$ and $\pi$N s wave scattering lengths and the $\pi^{0}$ lifetime. Recent, accurate pionic atom data are in agreement with chiral calculations once isospin breaking effects due to the mass difference of the up and down quarks are taken into account, as was required to extract the $\pi\pi$ scattering lengths. In addition to tests of the theory, comparisons between $\pi\pi$ and $\pi$N interactions based on general chiral principles are discussed. Lattice calculations are now providing results for the fundamental, long and inconclusively studied, $\pi$N $\sigma$ term and the contribution of the strange quark to the mass of the proton. Increasingly accurate experiments in electromagnetic pion production experiments from the proton which test ChPT calculations (and their energy region of validity) are presented. These experiments are also beginning to measure the final state $\pi$N interaction. This paper is based on the concluding remarks made at the Chiral Dynamics Workshop CD12 held at Jefferson Lab in Aug. 2012.
The Adaptive Value of Polymorphism in an Alpine Ant, FormicaNeorufibarbis Gelida Wheeler
Ruth A. Bernstein
Psyche , 1976, DOI: 10.1155/1976/52542
Abstract:
Light Quark Mass Difference and Isospin Breaking In Electromagnetic Pion Production
A. M. Bernstein
Physics , 1998, DOI: 10.1016/S0370-2693(98)01257-X
Abstract: It is demonstrated that there is a dynamic isospin breaking effect in the near threshold $\gamma^{*} N\to \pi N$ reaction due to the mass difference of the up and down quarks, which also causes isospin breaking in the $\pi N$ system. The photopion reaction is affected through final state $\pi N$ interactions (formally implemented by unitarity and time reversal invariance). It is also demonstrated that the near threshold $\gamma \vec{N} \to \pi N$ reaction is a practical reaction to measure isospin breaking in the $\pi N$ system, which was first predicted by Weinberg about 20 years ago but has never been experimentally tested.
Deviation of the Nucleon Shape From Spherical Symmetry: Experimental Status
A. M. Bernstein
Physics , 2002, DOI: 10.1140/epja/i2002-10176-7
Abstract: In this brief pedagogical overview the physical basis of the deviation of the nucleon shape from spherical symmetry will be presented along with the experimental methods used to determine it by the gamma* p -> Delta reaction.The fact that significant non-spherical electric(E2) and Coulomb quadrupole(C2) amplitudes have been observed will be demonstrated. These multipoles for the N,Delta system as a function of Q^2 from the photon point through 4 GeV^2 have been measured with modest precision. Their precise magnitude remains model dependent due to the contributions of the background amplitudes, although rapid progress is being made to reduce these uncertainties. A discussion of what is required to perform a model independent analysis is presented. All of the data to date are consistent with a prolate shape for the proton (larger at the poles) and an oblate shape(flatter at the poles) for the Delta. It is suggested here that the fundamental reason for this lies in the spontaneous breaking of chiral symmetry in QCD and the resulting, long range(low Q^2), effects of the pion cloud. This verification of this suggestion, as well as a more accurate measurement of the deviation from spherical symmetry, requires further experimental and theoretical effort.
The pi0, eta, eta' -> gamma gamma*(Q^2) Decay Rates and Radii
A. M. Bernstein
Physics , 2015,
Abstract: The low $Q^2$ slopes of the the transition form factors provide a unique method to measure the sizes of the neutral pseudo-scalar mesons, since they do not have electromagnetic form factors. From the slope one obtains the "axial transition RMS radius" $ R_{PS,A} = \sqrt{}$ for each PS meson. The present status of theory and experiment for these quantities are presented. A comparison of the $ R_{PS,A}$ is presented along with the electromagnetic and scalar radii of the $\pi^{\pm}$ mesons and the proton. We observe the striking similarity of the values of axial transition radii of all of the pseudoscalar mesons to each other and to the charge radius of the $\pi^{\pm}$. In the $Q^2$ = 0 limit the transition form factor is a measure of the pseudo-scalar meson radiative width (lifetime) and is a possible fourth (unexploited) method to perform such a measurement. The $\pi^{0} \rightarrow \gamma \gamma$ decay rate is a test of QCD at the confinement scale. There is a firm QCD prediction with a theoretical uncertainty of $\simeq $ 1 \% which calls for an experimental test at the same level of accuracy. There are three methods that have been utilized to perform this measurement and the present status of the experimental tests are outlined. The current accuracy is significantly less than the theoretical uncertainty. The efforts to improve this are briefly summarized.
Pions: Experimental Tests of Chiral Symmetry Breaking
A. M. Bernstein
Physics , 2013,
Abstract: Based on the spontaneous breaking of chiral symmetry, chiral perturbation theory (ChPT) is believed to approximate confinement scale QCD. Dedicated and increasingly accurate experiments and improving lattice calculations are confirming this belief, and we are entering a new era in which we can test confinement scale QCD in some well chosen reactions. This is demonstrated with an overview of low energy experimental tests of ChPT predictions of $\pi\pi$ scattering, pion properties, $\pi$N scattering and electromagnetic pion production. These predictions have been shown to be consistent with QCD in the meson sector by increasingly accurate lattice calculations. At present there is good agreement between experiment and ChPT calculations, including the $\pi\pi$ and $\pi$N s wave scattering lengths and the $\pi^{0}$ lifetime. Recent, accurate pionic atom data are in agreement with chiral calculations once isospin breaking effects due to the mass difference of the up and down quarks are taken into account, as was required to extract the $\pi\pi$ scattering lengths. In addition to tests of the theory, comparisons between $\pi\pi$ and $\pi$N interactions based on general chiral principles are discussed. Lattice calculations are now providing results for the fundamental, long and inconclusively studied, $\pi$N $\sigma$ term and the contribution of the strange quark to the mass of the proton. Increasingly accurate experiments in electromagnetic pion production experiments from the proton which test ChPT calculations (and their energy region of validity) are presented. These experiments are also beginning to measure the final state $\pi$N interaction. This paper is based on the concluding remarks made at the Chiral Dynamics Workshop CD12 held at Jefferson Lab in Aug. 2012.
Symmetry Tests in Photo-Pion Production
A. M. Bernstein
Physics , 2013, DOI: 10.1063/1.4829399
Abstract: Small angle electron scattering with intense electron beams opens up the possibility of performing almost real photon induced reactions with thin, polarized hydrogen and few body targets, allowing for the detection of low energy charged particles.This promises to be much more effective than conventional photon tagging techniques. For photo-pion reactions some fundamental new possibilities include: tests of charge symmetry in the N-N system by measurement of the neutron-neutron scattering length $a_{nn}$ in the $\gamma D \rightarrow \pi^{+} nn$ reaction; tests of isospin breaking due to the mass difference of the up and down quarks; measurements with polarized targets are sensitive to $\pi$N phase shifts and will test the validity of the Fermi-Watson (final state interaction) theorem. All of these experiments will test the accuracy and energy region of validity of chiral effective theories.
Energy Dependence of the Delta Resonance: Chiral Dynamics in Action
Bernstein, A. M.;Stave, S.
High Energy Physics - Phenomenology , 2007, DOI: 10.1007/s00601-007-0190-6
Abstract: There is an important connection between the low energy theorems of QCD and the energy dependence of the Delta resonance in pi-N scattering, as well as the closely related gamma^{*} N -> pi N reaction. The resonance shape is due not only to the strong pi-N interaction in the p wave but the small interaction in the s wave; the latter is due to spontaneous chiral symmetry breaking in QCD (i.e. the Nambu-Goldstone nature of the pion). A brief overview of experimental tests of chiral perturbation theory and chiral based models is presented
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