It is argued that exotic mesons consisting of two quarks and two antiquarks are not ruled out in quantum chromodynamics with a large number $N$ of colors, as generally thought. Tetraquarks of one class are typically long-lived, with decay rates proportional to $1/N$.

• Received 1 March 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.261601