0000000000823937
AUTHOR
H.c. Chiang
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and $K^-$ atoms.
Chiral unitary theory: Application to nuclear problems
In this talk we briefly describe some basic elements of chiral perturbation theory, $\chi PT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $ \pi \pi $ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $\phi$ meson properties are changed in a nuclear medium.
Muon capture revisited
Abstract The problem of inclusive muon capture in nuclei is studied by calculating the capture rate in asymmetric infinite nuclear matter and using the local density approximation to evaluate the capture rates in nuclei. It is shown that the method is rather reliable and allows one to improve on approximations used in the past. The need for a strong nuclear renormalization is shown, reducing the capture rates by about a factor two in medium and heavy nuclei. By using standard effective interactions in the spin-isospin channel one can account for this renormalization and one finds a remarkable overall agreement with the measured capture rates for a large list of nuclei through the periodic t…
Isoscalar S-wave π–π interaction in the nuclear medium
The s-wave isoscalar π π scattering amplitude in a nuclear medium has been evaluated using a non-perturbative unitary coupled channels method and the standard chiral Lagrangians. The method is successful describing the π π properties in vacuum, in the scalar-isoscalar channel up to 1.2 GeV giving rise to poles in the T matrix for the ƒ0(980) and the σ. The extension of the method to the nuclear medium implies the renormalization of the pions in the medium and also the introduction of interaction terms related to contact terms in the πN → ππN reaction. Vicente Vacas, Manuel Jose, Manuel.J.Vicente@ific.uv.es ; Oset Baguena , Eulogio, Eulogio.Oset@ific.uv.es
Chiral nonperturvative approach to the isoscalar s-wave pion-pion interaction in a nuclear medium
The s-wave isoscalar amplitude for pion-pion scattering in a nuclear medium is evaluated using a nonperturbative unitary coupled channels method and the standard chiral Lagrangians. The method has proved successful to describe the pion-pion properties in the scalar isoscalar channel up to 1.2 GeV giving rise to poles in the t matrix for the f0(980) and the sigma. The extension of the method to the nuclear medium implies not only the renormalization of the pions in the medium, but also the introduction of interaction terms related to contact terms in the pion-nucleon to pion-pion-nucleon interaction. Off shell effects are also shown to be important leading to cancellations which reduce the c…
Coherent and incoherent (μ−, e−) conversion in nuclei
Coherent and incoherent (μ−, e−) conversion in nuclei is studied within the framework of several theories which violate flavour lepton number. A useful approach is followed which allows a factorization of the conversion widths into nuclear factors and other factors which depend only on the elementary process. The nuclear factors are evaluated in a wide range of nuclei allowing simple calculations of the conversion rates throughout the periodic table for a given theory with a minimum of work in the elementary sector. The coherent conversion is found to dominate the process. The results obtained modify appreciable previous results in the literature, particularly in the incoherent process.