Identify the mechanism causing positive orbital-period derivatives

Identify the physical mechanism responsible for the positive orbital-period derivatives observed in nearly half of the measured cataclysmic variables.

Background

The paper reports that a substantial fraction of cataclysmic variables exhibit positive long-term orbital-period derivatives, contrary to the expectation that angular-momentum loss should make their periods decrease. The observed positive derivatives therefore challenge the assumed universality of period-shortening evolution.

The authors note that mass transfer and nova-related mass ejection can increase the orbital period, but they do not establish which process, or combination of processes, explains the observed positive derivatives across the broader cataclysmic-variable population.

References

We do not understand the mechanism for the positive-$\dot{P}$, but the orbital periods are increasing anyway.

— Classical Nova V1405 Cas Had $M_{\rm ejecta}$$>$$M_{\rm accreted}$ and so is Unlikely to be a Type Ia Supernova Progenitor  (2609.10990 - Schaefer, 10 Sep 2026) in Section 7.5, “CV evolution runs from long-P to short-P”