Delivering on a hype-filled week that included their live debut at the 12-12-12 Sandy Benefit and this weekend’s SNL performance, today Sir Paul McCartney and surviving Nirvana members Dave Grohl, Krist Novoselic, and Pat Smear shared their first official studio track, recorded for Grohl’s Sound City documentary. “Cut Me Some Slack” is completely charming: rocking out to near-“Helter Skelter” proportions while each player sounds inspired and — even more so — letting go to revel in the fun of an unexpected union. Paul says as much on lead vox: “Oh mama, let me be / Oh mama, watch me run / Mama, I wanna have some fun.”