The non-ordinary Regge behavior of the $f_0(500)$ meson
  We review how the Regge trajectory of an elastic resonance can be obtained just from its pole position and coupling, by means of a dispersive formalism. This allows to deal correctly with the finite widths of resonances in Regge trajectories. For the $\rho(770)$ meson this method leads to the ordinary linear Regge trajectory with a universal slope. In contrast, for the $f_0(500)$ meson, the resulting Regge trajectory is non-linear and with much smaller slope. This is another strong indication of the non-ordinary nature of the lightest scalar meson. 
J.R.Pel\'aez, J.T.Londergan, J. Nebreda, A.P.Szczepaniak
hep-ph nucl-th