I can liken the definition of art to the epiphenomenalist view of mind. The epiphenomenalist theory of mind says that mental states are emergent from brain states, but that those mental states exert no causal role on the physical brainstates from which they emerge. It can be said that mental states are like a shadow of brainstates.

I think what most people consider as "art" is like those shadows/mental states. The end product normally regarded as the art itself (a particular painting, film, musical piece, novel, etc. etc. etc.) is merely EMERGENT from the art, which exists purely in the moment of creation and can never exhibit temporal duration except as an emergent shadow (memory?) of the art, a mere reminder. It is in the moments of truly living in the present, of Dionysian intoxication in which reality is experienced unfiltered, that the most distinctive art is experienced and therefore great artworks produced. Art is an experience, not an end result.

Art is identitical to the present and is dead before it can ever be captured into a document that exhibits temporal duration. Art is life and life is art. The artworks that results is mere memory.