Strings in meson and baryon physics

The relativistic string with massive ends (the meson model) and four various string baryon models: q-qq, q-q-q, Y and ∆ are considered. In particular, the rotational motions for all these systems are applied to describing the leading Regge trajectories, and also the classical dynamics beyond the usual rectilinear string rotations is studied. For the string meson model the two types of quasirotational motions (disturbances of the planar uniform rotations) are obtained. They are oscillatory motions in the form of stationary waves in the rotational plane and in the orthogonal direction. The analysis of the stability problem for the rotational motions for all mentioned string configurations shows that these motions for the Y and q-q-q models are unstable on the classical level. In various string models of hadrons the relativistic string simulates the strong interaction between quarks at large distances and the QCD confinement mechanism [1]. One of the starting points for strings in particle physics was the natural explanation of linearly growing Regge trajectories for orbitally excited hadron states, where the Regge slope α = 1/(2πγ) is simply connected with the string tension γ. The string model of the meson is geometrically obvious, on the classic level it is the relativistic string with massive ends shown in Fig. 1 (a) [1]. But for the baryon we have four string models with different topology [2]: (b) the meson-like quark-diquark model q-qq [3], (c) the linear configuration q-q-q [4], (d) the “three-string” model or Y configuration [5], and (e) the “triangle” model or ∆ configuration [6].