"The song "White As Snow" from U2's latest album No Line on the Horizon, has been called their most intimate song and is a hymnal to a soldier dying in Afghanistan. It was written specifically for "Brothers" (Sheridan and Bono - Irish brethren - have a long history together, including Bono co-penning songs from "In America" and "In The Name of The Father"), but the band decided to release it on their new record after the film's many delays. The Guardian U.K. calls it, "unadorned, evocative and suggestive. And you don't even have to know what it's about to feel its quiet power or sense its sadness." Presumably it'll be featured in the film's credits.
Update: Apparently there's another song in "Brothers" written by U2 during the Horizon sessions that hasn't been released yet called, "Winter". The track can evidently be heard on the short film directed by Anton Corbijn that accompanies the album in the digipack format".