Effective Degrees of Freedom in Baryon and Meson Spectroscopy

We discuss some of the most relevant non-standard quark configurations in hadron spectroscopy, which are alternative to the qqq and qq¯\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$q \bar{q}$$\end{document} description of baryons and mesons, respectively. They include the quark-diquark and four-quark (five-quark) meson-meson (meson-baryon) bound states. To this purpose, we briefly review the diquark model of baryons and tetraquark states and the hadro-quarkonium model of heavy-light tetra- and pentaquarks. Some applications of the previous models are discussed.