Local Analysis of Nonlinear Oscillations of Thin Accretion Disks
  We calculated the coupling coefficients for non-linear, quasi-local oscillatory modes of thin accretion disks. We found that several of them are non-zero. Mode coupling is a necessary condition for a resonance, and thus our results may be relevant for the recently discussed QPO resonance model. 
Sara Fogelstr\"om, Lina Levin, Rikard Slapak