  Mass transfer in cataclysmic variables (CVs) is usually considered to be
caused by angular momentum loss (AML) driven by magnetic braking and
gravitational radiation (GR) above the period gap, and solely by GR below the
period gap. The best-fit revised model of CV evolution recently by
\citet{kbp11}, however, indicates that AML rate below the period gap is
$2.47(\pm 0.22)$ times the GR rate, suggesting the existence of some other AML
mechanisms. We consider several kinds of consequential AML mechanisms often
invoked in the literature: isotropic wind from the accreting white dwarfs,
outflows from the Langrangian points, and the formation of a circumbinary disk.
We found that neither isotropic wind from the white dwarf nor outflow from the
$L_1$ point can explain the extra AML rate, while ouflow from the $L_2$ point
or a circumbinary disk can effectively extract the angular momentum provided
that $\sim (15-45)%$ of the transferred mass is lost from the binary. A more
promising mechanism is a circumbinary disk exerting gravitational torque on the
binary. In this case the mass loss fraction can be as low as $\lesssim
10^{-3}$.
