798 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
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
How (not) to renormalize integral equations with singular potentials in effective field theory
We discuss the connection between the perturbative and non-perturbative
renormalization and related conceptual issues in the few-nucleon sector of the
low-energy effective field theory of the strong interactions. General arguments
are supported by examples from effective theories with and without pions as
dynamical degrees of freedom. A quantum mechanical potential with explicitly
specified short- and long-range parts is considered as an "underlying
fundamental theory" and the corresponding effective field theory potential is
constructed. Further, the problem of the effective field theoretical
renormalization of the Skornyakov-Ter-Martyrosian equation is revisited.Comment: 12 pages, 5 figure
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