We discuss theoretically the possibility of observing the bound states of the η and η (958) mesons in nuclei. We apply the NJL model to study the η and η meson properties at finite density and calculate the formation cross sections of the η and η bound states with the Green function method for (γ ,p) reaction. We also discuss the experimental feasibility at photon facilities like SPring-8. The contributions due to the ω meson production are also included to obtain the realistic (γ ,p) spectra. We conclude that we can expect to observe resonance peaks in (γ ,p) spectra for the formation of meson bound states and we can deduce new information on η and η properties at finite density. These observations are believed to be essential to know the possible mass shift of η and deduce new information on the effective restoration of the U A (1) anomaly in the nuclear medium.
The radiative decay of the axial-vector resonances into a pseudoscalar meson
and a photon is studied using the vector meson Lagrangian obtained from the
hidden gauge symmetry (HGS) formalism. The formalism is well suited to study
this problem since it deals with pseudoscalar and vector mesons in a unified
way, respecting chiral invariance. We show explicitly the gauge invariance of
the set of diagrams that appear in the approach and evaluate the radiative
decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi
gamma. We also include the contribution of loops involving anomalous couplings
and compare the results to those obtained previously within another formalism.Comment: 24 pages, 6 tables, 11 figure
International audienceWe review applications of effective field theory methods in a finite volume for the extraction of the characteristics of unstable particles from lattice QCD calculations. In particular, the scalar mesons f0(980),a0(980) are considered. We formulate criteria that distinguish between hadronic molecules and tightly bound quark states, as well as between the ordinary qq̄ and the tetraquark states. Using these criteria will enable one to study the nature of scalar mesons on the lattice. Further, we also formulate a procedure to calculate resonance matrix elements on the lattice by using the background field method
We study composite systems of light (ρ and ω) and heavy (D * ) vector mesons by using the interaction within the hidden gauge formalism. We find a strong attraction in the isospin, spin channels (I, S) = (1/2, 0); (1/2, 1); (1/2, 2) with positive parity. The attraction is large enough to strongly bind these mesons in states with these quantum numbers, leading to states which can be identified with D * 2 (2460) and probably with D * (2640), the last one without experimental spin and parity assignment. In the case of I = 3/2 one obtains repulsion and thus, no exotic mesons in this sector are generated in the approach.
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