We investigate the role of the delta isobar in the reaction πd → πd at threshold in chiral effect... more We investigate the role of the delta isobar in the reaction πd → πd at threshold in chiral effective field theory. We discuss the corresponding power counting and argue that this calculation completes the evaluation of diagrams up to the order χ 3/2 , with χ the ratio of the pion to the nucleon mass. The net effect of all delta contributions at this order to the pion-deuteron scattering length is δa ∆ πd = (2.4 ± 0.4) × 10 −3 m −1 π .
We calculate electromagnetic neutral pion production off three-nucleon bound states (3 H, 3 He) a... more We calculate electromagnetic neutral pion production off three-nucleon bound states (3 H, 3 He) at threshold to leading one-loop order in the framework of chiral nuclear effective field theory. In addition, we analyze the dependence of the nuclear S-wave amplitude E 0+ on the elementary neutron amplitude E π 0 n 0+ which in the case of 3 He provides a stringent test of the prediction based on chiral perturbation theory. Uncertainties from higher order corrections are estimated.
The European Physical Journal A - Hadrons and Nuclei, 2003
I discuss our knowledge of the scalar sector of QCD and how it impacts the determination of the C... more I discuss our knowledge of the scalar sector of QCD and how it impacts the determination of the CKM angle α from the isospin analysis of B → ρπ decay. 1 Introduction and motivation CP violation has been established experimentally in the K-and B-meson systems. In the Standard Model, this can be explained in terms of one single phase, which leads to complex entries in the CKM matrix. The unitarity of this matrix may be represented in terms of various triangles, one of them to be measured at the B-factories. Any violation of unitarity would be a signal of physiscs beyond the Standard Model. However, to achieve the required accuracy to really test the relation α + β + γ = π, where α, β, and γ are the three
The European Physical Journal A - Hadrons and Nuclei, 2003
I present and discuss recent results on elastic pion-nucleon scattering and near-threshold neutra... more I present and discuss recent results on elastic pion-nucleon scattering and near-threshold neutralpion electroproduction off deuterium obtained in the framework of chiral perturbation theory.
The momentum-space bosonization method is extended to the case of a Nambu-Jona-Lasinio type model... more The momentum-space bosonization method is extended to the case of a Nambu-Jona-Lasinio type model with vector and axial-vector mesons. The method presented gives the possibility of deriving any meson vertex function to all orders in momenta and to the leading order in 1/N c. Two-point functions, which describe one-particle transitions to the hadronic vacuum, and meson selfenergies are considered. We find new relations which generalize the well-known KSFR relation and both the first and the second Weinberg sum rules. These result from a consistent treatment of higher order terms in the momentum expansion.
The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field th... more The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field theory and fitted to ΛN and ΣN scattering data, are investigated. Results for the single-particle potentials of the Λ and Σ hyperons in nuclear matter are reported, based on a conventional G-matrix calculation. The Σ-nuclear potential is found to be repulsive, in agreement with phenomenological information. A weak Λ-nuclear spin-orbit interaction can be achieved by an appropriate adjustment of a low-energy constant corresponding to an antisymmetric ΛN-ΣN spin-orbit interaction that arises at next-to-leading order in the effective field theory approach.
We study the parity-violating pion-nucleon coupling G π in the framework of a realistic three fla... more We study the parity-violating pion-nucleon coupling G π in the framework of a realistic three flavor Skryme model. We find a sizeable enhancement of G π ≃ 0.8. .. 1.3 • 10 −7 compared to previous calculations in two-flavor models with vector mesons. This strangeness enhancement stems from induced kaon fields of the chiral soliton and the non-monotoneous dependence on symmetry breaking of the nucleon matrix element of the flavor singlet piece of the operator associated with these induced fields. Both features are sensitive to four quark operators including anss pair.
The possibility of imposing partially twisted boundary conditions is investigated for the scalar ... more The possibility of imposing partially twisted boundary conditions is investigated for the scalar sector of lattice QCD. According to the commonly shared belief, the presence of quark-antiquark annihilation diagrams in the intermediate state generally hinders the use of the partial twisting. Using effective field theory techniques in a finite volume, and studying the scalar sector of QCD with total isospin I = 1, we however demonstrate that partial twisting can still be performed, despite the fact that annihilation diagrams are present. The reason for this are delicate cancellations, which emerge due to the graded symmetry in partially quenched QCD with valence, sea and ghost quarks. The modified Lüscher equation in case of partial twisting is given.
We investigate the role of the delta isobar in the reaction πd → πd at threshold in chiral effect... more We investigate the role of the delta isobar in the reaction πd → πd at threshold in chiral effective field theory. We discuss the corresponding power counting and argue that this calculation completes the evaluation of diagrams up to the order χ 3/2 , with χ the ratio of the pion to the nucleon mass. The net effect of all delta contributions at this order to the pion-deuteron scattering length is δa ∆ πd = (2.4 ± 0.4) × 10 −3 m −1 π .
We calculate electromagnetic neutral pion production off three-nucleon bound states (3 H, 3 He) a... more We calculate electromagnetic neutral pion production off three-nucleon bound states (3 H, 3 He) at threshold to leading one-loop order in the framework of chiral nuclear effective field theory. In addition, we analyze the dependence of the nuclear S-wave amplitude E 0+ on the elementary neutron amplitude E π 0 n 0+ which in the case of 3 He provides a stringent test of the prediction based on chiral perturbation theory. Uncertainties from higher order corrections are estimated.
The European Physical Journal A - Hadrons and Nuclei, 2003
I discuss our knowledge of the scalar sector of QCD and how it impacts the determination of the C... more I discuss our knowledge of the scalar sector of QCD and how it impacts the determination of the CKM angle α from the isospin analysis of B → ρπ decay. 1 Introduction and motivation CP violation has been established experimentally in the K-and B-meson systems. In the Standard Model, this can be explained in terms of one single phase, which leads to complex entries in the CKM matrix. The unitarity of this matrix may be represented in terms of various triangles, one of them to be measured at the B-factories. Any violation of unitarity would be a signal of physiscs beyond the Standard Model. However, to achieve the required accuracy to really test the relation α + β + γ = π, where α, β, and γ are the three
The European Physical Journal A - Hadrons and Nuclei, 2003
I present and discuss recent results on elastic pion-nucleon scattering and near-threshold neutra... more I present and discuss recent results on elastic pion-nucleon scattering and near-threshold neutralpion electroproduction off deuterium obtained in the framework of chiral perturbation theory.
The momentum-space bosonization method is extended to the case of a Nambu-Jona-Lasinio type model... more The momentum-space bosonization method is extended to the case of a Nambu-Jona-Lasinio type model with vector and axial-vector mesons. The method presented gives the possibility of deriving any meson vertex function to all orders in momenta and to the leading order in 1/N c. Two-point functions, which describe one-particle transitions to the hadronic vacuum, and meson selfenergies are considered. We find new relations which generalize the well-known KSFR relation and both the first and the second Weinberg sum rules. These result from a consistent treatment of higher order terms in the momentum expansion.
The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field th... more The in-medium properties of a hyperon-nucleon potential, derived within chiral effective field theory and fitted to ΛN and ΣN scattering data, are investigated. Results for the single-particle potentials of the Λ and Σ hyperons in nuclear matter are reported, based on a conventional G-matrix calculation. The Σ-nuclear potential is found to be repulsive, in agreement with phenomenological information. A weak Λ-nuclear spin-orbit interaction can be achieved by an appropriate adjustment of a low-energy constant corresponding to an antisymmetric ΛN-ΣN spin-orbit interaction that arises at next-to-leading order in the effective field theory approach.
We study the parity-violating pion-nucleon coupling G π in the framework of a realistic three fla... more We study the parity-violating pion-nucleon coupling G π in the framework of a realistic three flavor Skryme model. We find a sizeable enhancement of G π ≃ 0.8. .. 1.3 • 10 −7 compared to previous calculations in two-flavor models with vector mesons. This strangeness enhancement stems from induced kaon fields of the chiral soliton and the non-monotoneous dependence on symmetry breaking of the nucleon matrix element of the flavor singlet piece of the operator associated with these induced fields. Both features are sensitive to four quark operators including anss pair.
The possibility of imposing partially twisted boundary conditions is investigated for the scalar ... more The possibility of imposing partially twisted boundary conditions is investigated for the scalar sector of lattice QCD. According to the commonly shared belief, the presence of quark-antiquark annihilation diagrams in the intermediate state generally hinders the use of the partial twisting. Using effective field theory techniques in a finite volume, and studying the scalar sector of QCD with total isospin I = 1, we however demonstrate that partial twisting can still be performed, despite the fact that annihilation diagrams are present. The reason for this are delicate cancellations, which emerge due to the graded symmetry in partially quenched QCD with valence, sea and ghost quarks. The modified Lüscher equation in case of partial twisting is given.
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Papers by Ulf-g Meissner