Two- and three-body descriptions of hybrid mesons

Hybrid mesons are exotic mesons in which the color field is not in its ground state. Their understanding deserves interest from a theoretical point of view, because it is intimately related to nonperturbative aspects of QCD. In this work, we analyze and compare two different descriptions of hybrid mesons, namely, a two-body $q\overline{q}$ system with an excited string, or a three-body $q\overline{q}g$ system. In particular, we show that the constituent gluon approach is equivalent to an effective excited string in the heavy hybrid sector. Instead of a numerical resolution, we use the auxiliary field technique. It allows us to find simplified analytical mass spectra and wave functions, and still leads to reliable qualitative predictions. We also investigate the light hybrid sector, and found a mass for the lightest hybrid meson which is in satisfactory agreement with lattice QCD and some effective models.