794 research outputs found
A unitary and causal effective field theory
We report on a novel scheme based on the chiral Lagrangian. It is used to
analyze pion-nucleon scattering, pion photoproduction, and nucleon Compton
scattering. Subthreshold partial-wave amplitudes are calculated in chiral
perturbation theory and analytically extrapolated with constraints imposed by
electromagnetic-gauge invariance, causality and unitarity. Experimental
quantities are reproduced up to energies MeV in terms of
the parameters relevant at order .Comment: 4 pages, contribution to the proceedings of the MENU 2010 conference,
May 31-June 4, 2010, Williamsburg VA, US
Unitary and causal dynamics based on the chiral Lagrangian
Pion-nucleon scattering, pion photoproduction, and nucleon Compton scattering
are analyzed within a scheme based on the chiral Lagrangian. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes computed in chiral perturbation theory, where the constraints set by
electromagnetic-gauge invariance, causality and unitarity are used to stabilize
the extrapolation. Experimental data are reproduced up to energies
MeV in terms of the parameters relevant at order . A
striking puzzle caused by an old photon asymmetry measurement close to the pion
production threshold is discussed.Comment: Invited plenary talk at Chiral 10 Workshop, Valencia (Spain), June
21-24, 201
Analysis of Cosequences of Faults in General Zero Transmission Lines of Power Supply Stations
Zero transmission line faults in power supply systems in large apartment houses, office blocks, offices and other structures cause voltage excursions,which are in the spotlight of this research. The phenomenon has been commented from the theoretical perspective, and emergency situations, which are likely to arise as a result ofmalfunction of single-phase power supply consumers, as well as the probable dangers of fire occurrences, have been revealed. We offer to install an appropriateprotective device to avoid such emergency situations
Three-nucleon force at large distances: Insights from chiral effective field theory and the large-N_c expansion
We confirm the claim of Ref. [D.R. Phillips, C. Schat, Phys. Rev. C88 (2013)
3, 034002] that 20 operators are sufficient to represent the most general local
isospin-invariant three-nucleon force and derive explicit relations between the
two sets of operators suggested in Refs. [D.R. Phillips, C. Schat, Phys. Rev.
C88 (2013) 3, 034002] and [H. Krebs, A.M. Gasparyan, E. Epelbaum, Phys.Rev. C87
(2013) 5, 054007]. We use the set of 20 operators to discuss the chiral
expansion of the long- and intermediate-range parts of the three-nucleon force
up to next-to-next-to-next-to-next-to-leading order in the standard formulation
without explicit Delta(1232) degrees of freedom. We also address implications
of the large-N_c expansion in QCD for the size of the various three-nucleon
force contributions.Comment: 15 pages, 6 figure
Two-nucleon scattering: merging chiral effective field theory with dispersion relations
We consider two-nucleon scattering close to threshold. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes calculated in a relativistic formulation of chiral perturbation
theory. The constraints set by unitarity are used in order to stabilize the
extrapolation. Neutron-proton phase shifts are analyzed up to laboratory
energies MeV based on the
next-to-next-to-next-to-leading order expression for the subthreshold
amplitudes. We find a reasonably accurate description of the empirical S- and
P-waves and a good convergence of our approach. These results support the
assumption that the subthreshold nucleon-nucleon scattering amplitude may be
computed perturbatively by means of the chiral expansion. The intricate soft
scales that govern the low-energy nucleon-nucleon scattering are generated
dynamically via a controlled analytic continuation.Comment: 10 pages, 5 figures, version accepted for publication, a more
detailed discussion of the results is adde
Two-nucleon scattering: merging chiral effective field theory with dispersion relations
We consider two-nucleon scattering close to threshold. Partial-wave
amplitudes are obtained by an analytic extrapolation of subthreshold reaction
amplitudes calculated in a relativistic formulation of chiral perturbation
theory. The constraints set by unitarity are used in order to stabilize the
extrapolation. Neutron-proton phase shifts are analyzed up to laboratory
energies MeV based on the
next-to-next-to-next-to-leading order expression for the subthreshold
amplitudes. We find a reasonably accurate description of the empirical S- and
P-waves and a good convergence of our approach. These results support the
assumption that the subthreshold nucleon-nucleon scattering amplitude may be
computed perturbatively by means of the chiral expansion. The intricate soft
scales that govern the low-energy nucleon-nucleon scattering are generated
dynamically via a controlled analytic continuation.Comment: 10 pages, 5 figures, version accepted for publication, a more
detailed discussion of the results is adde
Deuteron electromagnetic form factors in a renormalizable formulation of chiral effective field theory
We calculate the deuteron electromagnetic form factors in a modified version
of Weinberg's chiral effective field theory approach to the two-nucleon system.
We derive renormalizable integral equations for the deuteron without partial
wave decomposition. Deuteron form factors are extracted by applying the
Lehmann-Symanzik-Zimmermann reduction formalism to the three-point correlation
function of deuteron interpolating fields and the electromagnetic current
operator. Numerical results of a leading-order calculation with removed cutoff
regularization agree well with experimental data.Comment: 9 pages, 2 figure
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