What new styles and forms appeared in art music literature?

It's impossible to give a complete answer to this question without knowing what time period you're interested in. Art music has constantly evolved throughout history, with new styles and forms appearing in every era. To give you a more focused answer, please tell me:

* What time period are you interested in? For example, are you curious about the 20th century, the Renaissance, or the Baroque era?

* What kind of art music are you interested in? Are you focusing on classical music, opera, or something else?

Once I have this information, I can provide you with a more specific and helpful response.