scholarly journals MASS AND WIDTH OF THE σ

2007 ◽  
Vol 22 (02n03) ◽  
pp. 257-265 ◽  
Author(s):  
HEINRICH LEUTWYLER

I report on recent work done in collaboration with Irinel Caprini and Gilberto Colangelo1. We observe that the Roy equations lead to a representation of the ππ scattering amplitude that exclusively involves observable quantities, but is valid for complex values of s. At low energies, this representation is dominated by the contributions from the two subtraction constants, which are known to remarkable precision from the low energy theorems of chiral perturbation theory. Evaluating the remaining contributions on the basis of the available data, we demonstrate that the lowest resonance carries the quantum numbers of the vacuum and occurs in the vicinity of the threshold. Although the uncertainties in the data are substantial, the pole position can be calculated quite accurately, because it occurs in the region where the amplitude is dominated by the subtractions. The calculation neatly illustrates the fact that the dynamics of the Goldstone bosons is governed by the symmetries of QCD.

1993 ◽  
Vol 08 (17) ◽  
pp. 1599-1602 ◽  
Author(s):  
A.N. IVANOV ◽  
M. NAGY ◽  
N.I. TROITSKAYA

The probability of the K+→π+π0γ (DE) decay with the direct emission of a photon is calculated. The strong low-energy interactions are accounted for within chiral perturbation theory at the quark level, based on the Extended Nambu-Jona-Lasinio (ENJL) model approximating QCD at low energies. The dominant role of chiral anomalies is confirmed.


2020 ◽  
Vol 102 (9) ◽  
Author(s):  
Qin-He Yang ◽  
Wei Guo ◽  
Feng-Jun Ge ◽  
Bo Huang ◽  
Hao Liu ◽  
...  

1992 ◽  
Vol 07 (29) ◽  
pp. 7305-7338 ◽  
Author(s):  
A.N. IVANOV ◽  
M. NAGY ◽  
N.I. TROITSKAYA

The chiral perturbation theory is developed at the quark level within the extended Nambu-Jona-Lasinio model, which we used for the low-energy approximation of QCD in the leading order of the large N expansion. In terms of constituent-quark loop diagrams we analyze all of the main low-energy effects caused by the first order corrections in the current-quark-mass expansions. For the correct description of the η→3π decays we confirm the important role of the final-state interaction quoted by Gasser and Leutwyler.


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