Population synthesis tools are used to investigate the population of non magnetic cataclysmic variable binary systems with unevolved main sequence-like donors for systems above the upper edge of the period gap at orbital periods greater than 2.75 hr .
In addition to the angular momentum losses associated with gravitational radiation , magnetic braking , and mass loss from the system , we also include the effect of a circumbinary disk on the evolution of the binary system .
To calculate the orbital period distribution , a grid of detailed binary evolutionary sequences has been included in the simulations .
For a fractional mass input rate into the disk , corresponding to 3 \times 10 ^ { -4 } of the mass transfer rate , the model systems exhibit a bounce at orbital periods greater than 2.75 hr .
The simulations reveal that ( 1 ) some systems can exist as dwarf nova type systems throughout their lifetime , ( 2 ) dwarf nova type systems can evolve into nova-like systems as their mass transfer rate increases with increasing circumbinary disk mass , and ( 3 ) nova-like systems can evolve back into dwarf nova systems during their postbounce evolution to longer orbital periods .
Among these subclasses , nova-like cataclysmic variables would be the best candidates to search for circumbinary disks at wavelengths \gtrsim 10 \mu m .

The theoretical orbital period distribution of our population synthesis model is in reasonable accord with the combined population of dwarf novae and nova-like systems above the period gap , suggesting the possibility that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model .
The resulting population furthermore reveals the possible presence of systems with small mass ratios ( a property of systems exhibiting superhump phenomena at long orbital periods ) and a preference of O/Ne/Mg white dwarfs in dwarf nova systems in comparison to nova-like systems .
The nova-like population furthermore shows a lack of systems with high-mass white dwarfs .
The importance of observational bias in accounting for the differing populations is examined , and it is shown that an understanding of these effects is necessary in order to confront the theoretical distributions with the observed ones in a meaningful manner .