It's official - catchy songs are scientific matter. It's diagnosis: Stuck Song Syndrome.
Here is an abstract of the British journal of psychology from november 2009:
Abstract - Earworms ('stuck song syndrome'): Towards a natural history of intrusive thoughts:
Two studies examine the experience of 'earworms', unwanted catchy tunes that repeat. Survey data show that the experience is widespread but earworms are not generally considered problematic, although those who consider music to be important to them report earworms as longer, and harder to control, than those who consider music as less important. The tunes which produce these experiences vary considerably between individuals but are always familiar to those who experience them. A diary study confirms these findings and also indicates that, although earworm recurrence is relatively uncommon and unlikely to persist for longer than 24 h, the length of both the earworm and the earworm experience frequently exceed standard estimates of auditory memory capacity. Active attempts to block or eliminate the earworm are less successful than passive acceptance, consistent with Wegner's theory of ironic mental control.
Beaman CP, & Williams TI (2009). Earworms ('stuck song syndrome'): Towards a natural history of intrusive thoughts. British journal of psychology (London, England : 1953) PMID: 19948084