arXiv subjects

Pedro Bicudo

Publications and source records attributed to Pedro Bicudo.

94 records · Page 6Linked to original sources

arXiv2002

Analytic proof of the Weinberg theorem for off mass shell and composite pions

The Weinberg theorem for the pion-pion scattering is proved analytically in full detail for quark models in the ladder truncation. The proof is displayed with Feynman diagrams. The axial and vector Ward identities, for the quark propagator and for the ladder, exactly cancel any model dependence. Off mass shell and finite size effects are included in the quark-antiquark pion Bethe Salpeter vertices. This is applied to compute the isospin 0, 1 and 2 scattering matrices off the mass shell .

nucl-th↗

arXiv2001

Chirally symmetric quark description of low energy π-πscattering

Weinberg's theorem for π-πscattering, including the Adler zero at threshold in the chiral limit, is analytically proved for microscopic quark models that preserve chiral symmetry. Implementing Ward-Takahashi identities, the isospin 0 and 2 scattering lengths are derived in exact agreement with Weinberg's low energy results. Our proof applies to alternative quark formulations including the Hamiltonian and Euclidean space Dyson-Schwinger approaches. Finally, the threshold π-πscattering amplitudes are calculated using the Dyson-Schwinger equations in the rainbow-ladder truncation, confirming the formal derivation.

hep-ph↗

arXiv1999

The scalar meson puzzle beyond BCS

Les We present a new perspective on the scalar meson puzzle from spontaneous breaking of chiral symmetry beyond BCS. We find that going beyond BCS does not produce a systematic shift of the hadron spectrum. We also show that coupled channels reduce the breaking of chiral symmetry, with the same Feynman diagrams that appear in the coupling of a scalar meson to a pair of pseudoscalar mesons. With a Lattice QCD inspired quark-quark interaction, we find that the groundstate I=0, 3P0 quark antiquark meson is the f0(980) with a partial decay width of 40MeV. We also find a 30% reduction of the chiral condensate due to coupled channels.

hep-ph↗

arXiv1999

A new Perspective on the Scalar meson Puzzle, from Spontaneous Chiral Symmetry Breaking Beyond BCS

We introduce coupled channels of Bethe-Salpeter mesons both in the boundstate equation for mesons and in the mass gap equation for chiral symmetry. Consistency is insured by the Ward Identities for axial currents, which preserve the Goldstone boson nature of the pion and prevents a systematic shift of the hadron spectrum. We study the decay of a scalar meson coupled to a pair of pseudoscalars. We also show that coupled channels reduce the breaking of chiral symmetry, with the same Feynman diagrams that appear in the coupling of a scalar meson to a pair of pseudoscalar mesons. Exact calculations are performed in a particular confining quark model, where we find that the groundstate $I=0, ^3P_0 q \bar q$ meson is the f_0(980) with a partial decay width of 40MeV. We also find a 30% reduction of the chiral condensate due to coupled channels.

nucl-th↗