  The white dwarf (WD) mass distribution of cataclysmic variables (CVs) has
recently been found to dramatically disagree with the predictions of the
standard CV formation model. The high mean WD mass among CVs is not imprinted
in the currently observed sample of CV progenitors and cannot be attributed to
selection effects. Two possibilities have been put forward: either the WD grows
in mass during CV evolution, or in a significant fraction of cases, CV
formation is preceded by a (short) phase of thermal time-scale mass transfer
(TTMT) in which the WD gains a sufficient amount of mass. We investigate if
either of these two scenarios can bring theoretical predictions and
observations into agreement. We employed binary population synthesis models to
simulate the present intrinsic CV population. We incorporated aspects specific
to CV evolution such as an appropriate mass-radius relation of the donor star
and a more detailed prescription for the critical mass ratio for dynamically
unstable mass transfer. We also implemented a previously suggested wind from
the surface of the WD during TTMT and tested the idea of WD mass growth during
the CV phase by arbitrarily changing the accretion efficiency. We compare the
model predictions with the characteristics of CVs derived from observed
samples. We find that mass growth of the WDs in CVs fails to reproduce the
observed WD mass distribution. In the case of TTMT, we are able to produce a
large number of massive WDs if we assume significant mass loss from the surface
of the WD during the TTMT phase. However, the model still produces too many CVs
with helium WDs. Moreover, the donor stars are evolved in many of these
post-TTMT CVs, which contradicts the observations. We conclude that in our
current framework of CV evolution neither TTMT nor WD mass growth can fully
explain either the observed WD mass or the period distribution in CVs.
