Abstract: Galaxy mergers have a key role in the evolution of galaxies, specially at high-z when they were more common than today. Mergers trigger starbursts and AGN, which are both regulated by negative feedback processes, as well as can turn spiral galaxies into massive quiescent objects. The local counterparts of these major mergers are local ULIRGs (L(IR)/Lsun > 1e12) which, thanks to their proximity, allow us detailed studies of the dominant physical processes. In this talk, I will present the first ALMA results obtained for a sample of 25 local ULIRGs observed as part of the PUMA project. The ALMA 50-400pc (40-350 mas) observations reveal massive cold molecular outflows and the presence of X-ray/mid-IR elusive, but very luminous, deeply dust embedded AGN in these systems.