  We discuss the multi-wavelength predictions of the two models proposed for SU
UMa stars, i.e the enhanced mass transfer (EMT) and the tidal thermal
instability (TTI) models. We focus on the systematic differences of the
suggested scenarios before discussing the model predictions together with the
observations of the best-studied SU UMa system, VW Hyi. We find that assuming
the standard form of the viscosity parameter alpha, both models predict only
outbursts being triggered at the inner edge of the accretion disc. In the TTI
model the superoutbursts are triggered when the outer radius of the disc
reaches a certain value, i.e. the 3:1 resonance radius. In contrast, the EMT
scenario predicts superoutbursts when the disc mass exceeds a critical value.
This causes the EMT model to be much more sensitive to mass transfer variations
than the TTI model. In both models we find the predicted UV and EUV delays in
agreement with the observations of VW Hyi for alpha_hot/alpha_cold<=4. In
addition both models can generate precursor outbursts which are more pronounced
at short wavelengths, in agreement with observations. Variations found in the
observed light curve of single systems (e.g. VW Hyi) as well as the difference
between ordinary SU UMa stars and ER UMa systems are a natural outcome of the
EMT model while the TTI model fails to explain them.

Astrophysics