Clarify mode-coupling mechanisms in non-axisymmetric disc-oscillation models

Clarify the physical mechanisms that couple axisymmetric and non-axisymmetric modes, as well as pairs of non-axisymmetric modes, in the Non-axisymmetric Disc Oscillation Models.

Background

The NADO1 and NADO2 models describe HFQPOs through oscillation modes in a pressure-supported fluid torus, including modes with nonzero azimuthal wave number. Their frequency assignments require nonlinear interactions among axisymmetric and non-axisymmetric modes.

Although these models incorporate pressure effects and can reproduce relevant frequency relations, the dynamical origin of the required couplings has not been established. This limits their predictive power and leaves the physical basis of the models unresolved.

References

Although these models provide a natural framework for incorporating pressure effects and non-axisymmetric oscillations, their physical basis remains uncertain. In particular, the mechanisms responsible for coupling an axisymmetric mode to a non-axisymmetric mode, or coupling pairs of non-axisymmetric modes, are not yet well understood, limiting the predictive power of the model .

— Probing hairy Kerr black holes through quasi-periodic oscillations II: a study based on the resonance models  (2610.11378 - Dasgupta et al., 8 Oct 2026) in Section 3, subsection “Non-axisymmetric Disc Oscillation Model (NADO)”