Helicity Amplitudes of the Λ(1670) and two Λ(1405) as dynamically generated resonances

We determine the helicity amplitudes A1/2 and radiative decay widths in the transition Λ(1670) → γY (Y = Λ or Σ). The Λ(1670) is treated as a dynamically generated resonance in mesonbaryon chiral dynamics. We obtain the radiative decay widths of the Λ(1670) to γΛ as 3 ± 2 keV and to γΣ as 120 ± 50 keV. Also, the Q dependence of the helicity amplitudes A1/2 is calculated. We find that the KΞ component in the Λ(1670) structure, mainly responsible for the dynamical generation of this resonance, is also responsible for the significant suppression of the decay ratio ΓγΛ/ΓγΣ0 . A measurement of the ratio would, thus, provide direct access to the nature of the Λ(1670). To compare the result for the Λ(1670), we calculate the helicity amplitudes A1/2 for the two states of the Λ(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 A1/2. PACS. 13.40.Hq Electromagnetic decays – 14.20.Jn Hyperons – 24.10.Eq Coupled-channel and distortedwave models – 25.20.Lj Photoproduction reactions – 11.30.Rd Chiral Symmetry