https://doi.org/10.1140/epja/i2010-11015-0
Regular Article - Theoretical Physics
Helicity amplitudes of the 
(1670) and two (1405) as dynamically generated resonances
1
Institut für Kernphysik and Jülich Center for Hadron Physics, Forschungszentrum Jülich, D-52425, Jülich, Germany
2
Yukawa Institute for Theoretical Physics, Kyoto University, 606-8502, Kyoto, Japan
3
Departamento de Fısica Teórica and IFIC, Centro Mixto Universidad de Valencia-CSIC, Institutos de Investigación de Paterna, Aptdo. 22085, 46071, Valencia, Spain
* e-mail: m.doering@fz-juelich.de
Received:
19
February
2010
Revised:
27
April
2010
Accepted:
24
June
2010
Published online:
22
July
2010
We determine the helicity amplitudes A
1/2 and radiative decay widths in the transition (1670) 
Y (Y = or 
. The (1670) is treated as a dynamically generated resonance in meson-baryon chiral dynamics. We obtain the radiative decay widths of the (1670) to
as 2±1 keV and to
as 120±50 keV. Also, the Q2-dependence of the helicity amplitudes A
1/2 is calculated. We find that the K
component in the (1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio 
/
. A measurement of the ratio would, thus, provide direct access to the nature of the (1670) . To compare the result for the (1670) , we calculate the helicity amplitudes A
1/2 for the two states of the (1405) . Also, the analytic continuation of Feynman parameterized integrals of more complicated loop amplitudes to the complex plane is developed which allows for an internally consistent evaluation of A
1/2 .
© SIF, Springer-Verlag Berlin Heidelberg, 2010
