U2's next album will be "sci-fi".
The 'With or Without You' group, fronted by singer Bono, worked with Lady Gaga producer RedOne on tracks for their next record, resulting in a "futuristic" sound.
RedOne said: "Bono described the album as 'futuristic'. U2 going sci-fi or something, that's how he described it.
"We've put down a few ideas, but we don't know how many will end up on there.
"They have a very special way of working. A song is never done until the day before it comes out almost, so you never know."
Despite his work with 'Born This Way' hitmaker Gaga being mainly synthesiser led, the producer added the new material with U2 - which also includes guitarist The Edge, bass player Adam Clayton and drummer Larry Mullen - will be guitar based.
He added to Billboard.com: "I'm a guitar player, so it was just me and Bono and Edge playing guitar, exchanging melodies. We were just like musicians jamming. I loved it."
RedOne's tracks are most likely to appear on a new "club" record the group are working on, which is they have said is separate to a new rock album the band are writing called 'Songs Of Ascent' and the soundtrack to the 'Spiderman: Turn off the Dark' musical, which was written by The Edge and Bono.