Nature of χ_{c1}(3872) and T_{cc}^{+}(3875)

Two decades ago the χ_{c1}(3872) state was discovered in the hadron spectrum with two heavy quarks. The discovery fueled a surge in experimental research, uncovering dozens of so called XYZ exotics states lying outside the conventional quark model, as well as theoretical investigations into new forms of matter, such as quark-gluon hybrids, tetraquarks, and pentaquarks, with the potential of disclosing new information about the fundamental strong force. Among the XYZs, the χ_{c1}(3872) and T_{cc}^{+}(3875) states stand out for their striking characteristics and unleashed many discussions about their nature. Here, we address this question using the Born-Oppenheimer effective field theory (BOEFT) and show how QCD settles the issue of their composition. Not only do we describe well the main features of the χ_{c1}(3872) and T_{cc}^{+}(3875) states, but we also obtain predictions in the bottomonium sector. This opens the way to systematic applications of BOEFT to all XYZs.