Recent diboson and multiboson results in ATLAS

Recent measurements of the associated production of two or three massive vector bosons in proton--proton collisions at the Large Hadron Collider, collected by the ATLAS detector at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, are reported. The diboson analyses target the production and decay modes $WW\rightarrow e\nu_e\mu\nu_\mu$, $WZ \rightarrow \ell^{\prime} \nu \ell \ell\,(\ell = e, \mu)$, $ZZ \rightarrow \ell\ell\nu\nu$, and the $4\ell$ final state. Fiducial inclusive cross sections are compared to state-of-the-art Standard Model calculations and several unfolded differential distributions are measured. In the $WZ$ channel, the helicities of the $W$ and $Z$ bosons are probed. Results are interpreted in terms of limits on anomalous gauge couplings in the framework of effective field theories. Finally, the first evidence for the production of three massive vector bosons ($WWW$, $WWZ$, $WZZ$) is presented.