Since 2003, when the Belle Collaboration discovered the X(3872) - an enigmatic state in the spectrum of charmonium with the properties at odds with the predictions of the quark model, a new era in the spectroscopy of hadrons containing heavy quarks began. Since then, many new states in the spectrum of charmonium and bottomonium have been discovered which do not fit into the quark model scheme and as such qualify as exotic states. Most of such states are narrow and reside near strong open-flavour thresholds, which therefore leave imprint on their properties. I will discuss the theoretical approach to exotic states with heavy quarks based on the Effective Field Theory (EFT) and address some relevant specific issues such as the role of coupled channels, multibody dynamics, low-energy expansion of the amplitude, interplay of the quark and hadronic degrees of freedom, and so on. Theoretical analysis of the experimental and lattice data for the double-charm state Tcc+ found recently by the LHCb collaboration at CERN will be considered as a paradigmatic example.

Alexey Nefediev，researcher from HISKP of Bonn University, working mainly on theoretical studies in hadronic physics, analysis and interpretation of the experimental and lattice data, prediction of new hadronic states and their properties, and so on. He obtained his PhD degree in 1999 at the Institute of Theoretical and Experimental Physics (Moscow, Russia). From 2000 to 2002, he was a postdoctoral researcher at the Instituto Superior Tecnico (Lisbon, Portugal). From 2002, he took a permanent position as a Senior Scientist at the Institute for Theoretical and Experimental Physics (Moscow). In 2017, he obtained his second scientific degree adopted in Russia, Doctor of Sciences (habilitation). In 2018, he occupied a permanent position as a Leading Scientist at P.N.Lebedev Institute of the Russian Academy of Sciences (Moscow). Since 2022, he has been holding the position of a Scientific Advisor at the Institute Josef Stefan, Ljubljana, Slovania.