Frontman says his 2015 album does not spell the end for Las Vegas band
Frontman is working with Ariel Rechtshaid on follow up to 2010's 'Flamingo'
US band performed their take on hit single during headline slot
Las Vegas group played 19-song set at intimate O2 Academy gig
Haim's frontwoman played the song 'On Top' with Brandon Flowers and co
The Las Vegas rockers' track 'Human' beats songs by The Beatles, Oasis and Michael Jackson
Band will perform at O2 Academy on August 15
The Las Vegas group will headline Bellahouston Park on August 19
The performances make up part of a short film about Cash's new posthumous release
Lily Allen, Blondie, Kaiser Chiefs, Chic and Elbow will also appear at the two day event