Exotic Hadrons with Heavy Flavors -X, Y, Z and Related States-

In the past decade, exotic hadrons with charm and bottom flavors have been extensively studied both in experiments and in theories. In this review, we provide topical discussions by selecting $X,Y,Z$ particles, to which Belle has made important contributions. These are $X(3872)$, $Y(4260)$, $Z_c(4430{)}^{+}$, $Z_c(3900{)}^{+}$, $Z_b(10610{)}^{+}$ and $Z_b(10650{)}^{+}$. Based on the current experimental observations, we discuss those states with emphasis on hadronic molecule whose dynamics is governed by chiral symmetry and heavy-quark symmetry of QCD. We also mention briefly various interpretations and some theoretical predictions for the yet undiscovered exotic hadrons.