Two studies come to mind:
1) (recent) scientists discover that after 4 drinks, members of the opposite sex appear 25% more attractive. [your tax dollars at work]
2) out of a random selection of facial images, the image chosen most often as "beautiful" was the one that averaged all the other images.
There is a rhythm and pattern to the universe. When we experience that pattern in concentrated form, be it image, sound, or touch, it is "beautiful". That seems to me to be a common denominator.
More electic tastes are idiosyncratic, and may be described as beautiful by a subset of the population, but the percentile classifying such works is smaller than the common denominator.
For me, the answer is simple. F*** what others think is beautiful, what do I think it beautiful? It's a cliche, but beauty is ultimately subjective.
If you want to make a living selling art, be average, that's the lesson here (average in appeal, not in impact or Pirsig's "quality"). But that doesn't answer the question of what is art? To me, art evokes emotion, and if you can evoke emotion, you have created beauty, ceterus paribus, and that is all you need.
That, and 6 margaritas.