Ulf-G. Meissner

Chiral dynamics in nucleons and nuclei

We review the implications of the spontaneous chiral symmetry breaking in QCD for processes involving one, two, or more nucleons.

Chiral Perturbation Theory

This review gives a brief introduction to chiral perturbation theory in its various settings. We discuss some applications of recent interest, including chiral extrapolations for lattice gauge theory.

QCD accurately predicts the induced pseudoscalar coupling constant

Using chiral Ward identities of QCD, we derive a relation for the induced pseudoscalar coupling constant which is accurate within a few percent,

Infrared regularization for spin-1 fields

{\mathit{g}}_{\mathit{P}}

Infrared regularization with spin 3/2 fields

=8.44\ifmmode\pm\else\textpm\fi{}0.23.

Pion photoproduction off the proton in a gauge-invariant chiral unitary framework

Abstract.We extend the method of infrared regularization to spin-1 fields. As applications, we discuss the chiral extrapolation of the rho meson mass from lattice QCD data and the pion-rho sigma term.

CHIRAL LAGRANGIANS FOR BARYONS COUPLED TO MASSIVE SPIN-1 FIELDS

Abstract We present a Lorentz-invariant formulation of baryon chiral perturbation theory including spin-3/2 fields. Particular attention is paid to the projection on the spin-3/2 components of the delta fields. We also discuss the nucleon mass and the pion–nucleon sigma term.

Isospin dependence of the three-nucleon force

We investigate pion photoproduction off the proton in a manifestly gauge-invariant chiral unitary extension of chiral perturbation theory. In a first step, we consider meson-baryon scattering taking into account all next-to-leading order contact interactions. The resulting low-energy constants are determined by a fit to s-wave pion-nucleon scattering and the low-energy data for the reaction pi- p --> eta n. To assess the theoretical uncertainty, we perform two different fit strategies. Having determined the low-energy constants, we then analyse the data on the s-wave multipole amplitudes E0+ of pion and eta photoproduction. These are parameter-free predictions, as the two new low-energy constants are determined by the neutron and proton magnetic moments.

Isospin-violating nucleon-nucleon forces using the method of unitary transformation

We analyze the effective low energy field theory of Goldstone bosons and baryons chirally coupled to massive spin-1 fields. We use the electromagnetic baryon form factors to demonstrate the formal equivalence between the vector and the tensor field formulation for the spin-1 fields. We also discuss the origin of the so-called Weinberg term in pion–nucleon scattering and the role of ρ meson exchange. Chirally coupled vector mesons do not give rise to this two-pion nucleon seagull interaction but rather to higher order corrections. Some problems of the formal equivalence arising in higher orders and related to loops are touched upon.

On-shell consistency of the Rarita-Schwinger field formulation

We classify A-nucleon forces according to their isospin dependence and discuss the most general isospin structure of the three-nucleon force. We derive the leading and subleading isospin-breaking corrections to the three-nucleon force using the framework of chiral effective field theory.