On the extraction of the quark mass ratio (m_d - m_u)/m_s from   Gamma(eta' -> pi^0 pi^+ pi^-)/Gamma(eta' -> eta pi^+ pi^-)
  The claim that the light quark mass ratio (m_d - m_u)/m_s can be extracted from the decay width ratio Gamma(eta' -> pi^0 pi^+ pi^-)/Gamma(eta' -> eta pi^+ pi^-) is critically investigated within a U(3) chiral unitary framework. The influence of the recent VES data on the eta' -> eta pi^+ pi^- decay is also discussed. 
B. Borasoy, Ulf-G. Mei{\ss}ner, R. Ni{\ss}ler