AFTER A THREE-DECADE RUN, popular rock band R.E.M. split in 2011. But its members kept on playing. Guitarist Peter Buck, 69, has been especially busy since then, performing with numerous acts. And bassist Mike Mills, 67, recently formed a supergroup called Howl Owl Howl with Darius Rucker from Hootie & the Blowfish and Steve Gorman from the Black Crowes. “When the band broke up, I had to try to figure out who I was,” Mills says. “As soon as I decided to keep playing, the opportunities came along.” Here is a look at the band members’ post-breakup music projects. —Craig Rosen