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Search Results: 1 - 10 of 144473 matches for " F. Myhrer "
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The spin content of the proton
Myhrer, F.
High Energy Physics - Phenomenology , 2008, DOI: 10.1063/1.3215657
Abstract: Considerable progress has been made in our knowledge of the spin distribution within the proton. The recently measured limits on polarized gluons in the proton suggest polarized gluons contribute very modestly to the proton spin. We will show that a modern, relativistic and chirally symmetric description of the nucleon structure naturally explain the current proton spin data. Most of the "missing" spin is carried by confined quark and antiquarks' angular momentum.
Effective field theory and electro-weak processes
F. Myhrer
Physics , 2010, DOI: 10.1063/1.3479360
Abstract: Heavy baryon chiral perturbation theory is applied to one- and two nucleon processes.
Large two-pion-exchange contributions to the $pp\to ppπ^0$ reaction
F. Myhrer
Physics , 2006,
Abstract: The large two-pion exchange amplitudes are calculated in HB$\chi$PT and their net contribution to the reaction cross section is large.
Two-pion-exchange effects in the $pp\to ppπ^0$ reaction
F. Myhrer
Physics , 2007,
Abstract: We study the pp \to pp\pi^0 reaction near threshold based on heavy-baryon chiral perturbation theory. We show that the two-pion-exchange diagrams give much larger contribution than the one-pion-exchange diagram which is of lower chiral order in Weinberg's counting scheme. We also discuss the relation of our results to the momentum counting scheme.
What have we learned from antiproton proton scattering?
F. Myhrer
Physics , 1996, DOI: 10.1016/S0920-5632(97)00246-6
Abstract: From recent charge exchange measurements in the extreme forward direction, an independent and precise determination of the pion nucleon coupling constant is possible. This determination has reopened the debate on the value of this fundamental coupling constant of nuclear physics. Precise measurements of charge exchange observables at forward angles below 900 MeV/c would also give a better understanding of the long range part of the two-pion exchange potential. For example, the confirmation of the coherence of the tensor forces from the pion exchange and the isovector two-pion exchange would be very valuable. With the present data first attempts at an $\NbarN$ partial wave analysis have been made where, as in nucleon nucleon scattering, the antinucleon nucleon high J partial waves are mainly given by one-pion exchange. Finally a recent $\pbarp$ atomic cascade calculation and the fraction of P-state annihilation in gas targets is commented on.
Exclusive Hadronic Reactions at High $Q^2$ ($90\degree$) and Polarization Phenomena, An Experimental Proposal}
F. Myhrer
Physics , 1993,
Abstract: Arguments are presented for the expected behaviour of $\piNpiN$ scattering and the $\pbarppipi$ reaction at high energy and large scattering angles. % The annihilation reaction has close to maximal asymmetry ($\approx$ 1) for $p_{lab} \siml $ 2.2 GeV/c. % As will be presented for fixed (90$\degree$) angle this large asymmetry will not become zero but will start to oscillate with energy at higher energies and large $Q^2$ when perturbative QCD becomes applicable. This is due to the energy dependence of a QCD phase difference between the independent quark-quark scattering (Landshoff) and short-distance processes at high but not asymptotic energies. % A consequence of the existence the Landshoff process is that even if helicity is conserved at the quark level ($m_{q}$ = 0 MeV), helicity does not have to be conserved on the hadronic level. % We will discuss the implications for spin observables in $pp$ elastic scattering and argue that
Chiral Perturbation Theory and Nuclear Physics
F. Myhrer
Physics , 1997,
Abstract: Chiral symmetry serves as a guiding principle in low-energy hadron dynamics. An effective lagrangian, which explicitly breaks chiral symmetry via a small mass term, allows for a systematic method of calculating higher order corrections to tree-level results. This is applied to radiative muon capture on hydrogen, %to extract the weak pseudoscalar form factor, and to proton-proton $\pi^0$ production near threshold. Both processes pose theoretical challenges in light of recent experimental results.
Exclusive Hadronic Reactions at High $Q^2$
F. Myhrer
Physics , 1999,
Abstract: The observed scaling laws for large angle exclusive hadronic reactions are successfully accounted for by the short-distance QCD quark interchange processes. We focus on three hadronic reactions which shows evidence for a slight oscillatory deviation from the expected scaling behaviour. Possible explanations for these oscillations and connections to spin observables will be mentioned. Better data from excisting facilities (or a possible future KEK proton accelerator, JHP) can clarify the theoretical situation.
Comments on the electromagnetic decay of $Λ(1520)$
F. Myhrer
Physics , 2006, DOI: 10.1103/PhysRevC.74.065202
Abstract: The electromagnetic decay processes of excited hyperon states are a very sensitive probe of the structure of hyperons. We will argue that the recent measurements of electromagnetic decay rates indicate that the wave functions of the hyperon ground states should contain sizeable components of excited quark states (configuration mixing). Flavor-SU(3) is a broken symmetry and it appears that the hyperon wave functions should preferably be written in a $uds$-basis, where only the light $u$ and $d$ quarks are symmetrized, and not in the usual SU(6)-basis.
Electromagnetic Decays of Hyperons (II)
Y. Umino,F. Myhrer
Physics , 1992, DOI: 10.1016/0375-9474(93)90248-V
Abstract: Excited negative parity hyperon masses are calculated in a chiral bag model in which the pion and the kaon fields are treated as perturbations. We also calculate the hadronic widths of $\lama$ and $\lamb$ as well as the coupling constants of the lightest $I=0$ excited hyperon to the meson-baryon channels, and discuss how the dispersive effects of the hadronic meson-baryon decay channels affect the excited hyperon masses. Meson cloud corrections to the electromagnetic decay widths of the two lightest excited hyperons into ground states $\lamz$ and $\sigz$ are calculated within the same model and are found to be small. Our results strengthen the argument that predictions of these hyperon radiative decay widths provide an excellent test for various quark models of hadrons.
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