Test of the multiquark structure of $a_1(1420)$ in strong two-body decays

We present an analysis of strong two-body decays of the $a_1(1420)$ with $J^{PC}=1^{++}$ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the $a_1$ is an unusual state with a four-quark $q\bar{q}s\bar{s}$ structure we consider two possible configurations for this state — hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the $a_1$ is the decay into $K$ and $K^{\ast }$. In particular, we calculate that the four decay modes $a_1\to VP$ with $VP=K^{\ast \pm }{K}^{\mp }$, $K^{\ast 0}{\bar{K}}^0$, ${\bar{K}}^{\ast 0}{K}^0$ together give a dominant contribution to the measured total width of about 150 MeV. The observational mode $a_1\to f_0(980)+{\pi }^0$ is significantly suppressed by one order of magnitude.