Understand
The typical AdS/QCD models deal with the large-N_c limit of QCD, as a consequence the meson spectrum consists of the infinite number of states that is far from the real situation.
- Basing on introduction of anharmonic corrections to the holographic potential, the corrections whose existence has been recently advocated, we construct a class of bottom-up holographic models describing arbitrary finite number of states in the sector of light mesons.
- Within the proposed approach, the spectrum of masses square has the following properties: It is linear, $m_n^2\sim n$, at not very large n, nonlinear at larger n, with the nonlinear corrections being subleading in 1/N_c, has a limiting mass, and the number of states is proportional to N_c.
- The considered holographic models reflect thereby the merging of resonances into continuum and the breaking of gluon string at sufficiently large quark-antiquark separation that causes the linear Regge trajectories to bend down.