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Period bouncers are cataclysmic variables (CVs) that have evolved past theirorbital period minimum. The strong disagreement between theory and observationsof the relative fraction of period bouncers is a severe shortcoming in theunderstanding of CV evolution. We test the implications of the hypothesis thatmagnetic braking (MB), which is suggested to be an additional angular momentumloss (AML) mechanism for CVs below the period gap ($P_\mathrm{orb}\lesssim 120$min), weakens around their period minimum. We compute the evolution of CVdonors below the period gap using the MESA code, assuming that the evolution ofthe system is driven by AML by gravitational wave radiation (GWR) and MB. Weparametrize the MB strength as $\mathrm{AML_{MB}}=\kappa\mathrm{AML_{GWR}}$. Wecompute two qualitatively different sets of models, one where $\kappa$ is aconstant and the other where $\kappa$ depends on stellar parameters. We findthat in the latter set of models, $\kappa$ decreases as the CV approaches theperiod minimum ($P_\mathrm{orb}\approx80\,$ min), beyond which$\kappa\approx0$. This stalls their evolution so that they spend a long time inthe observed period minimum spike ($80\lesssimP_\mathrm{orb}/\,\mathrm{min}\lesssim 86$). Here they become difficult todistinguish from pre-bounce systems in the spike. A strong decrease inmass-transfer rate makes them virtually undetectable as they evolve further. Wealso discuss the physical processes, such as dynamo action, white dwarfmagnetism and dead zones, that may cause such a weakening of MB at shortorbital periods. The weakening magnetic braking formalism solves the problem ofthe lack of period bouncers in CV observational surveys.

Weakening of magnetic braking in cataclysmic variables explains the dearth of period bouncers