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SEZIONE DI FIRENZE The understanding of strongly coupled systems is one of the most challenging problems in particle physics.
The strong interactions between the quarks, as well as their confinement, pose substantial challenges. Especially this makes the study of hadrons as composite objects very difficult. The dynamical symmetry breaking of the chiral symmetry is another aspect of QCD which is not fully understood.
Hadrons are usually classified as quarkantiquark pairs (mesons), or quark triplets (baryons). However, there is no reason why these two combinations alone should exhaust the possibilities for the quarks to bind together.
This indeed has been set to reconsideration by the discovery of several exotic X, Y, Z resonances in the quarkonium sector. Although much of the understanding of the QCD spectrum comes from phenomenological models, significant theoretical suggestions derive from the gaugegravity correspondence, or the use of DysonSchwinger Equations, or from the study of QCD in the planar (large Nc) limit. Also, Lattice QCD is becoming a more and more reliable tool to check the predictions of the various models and approaches.
At higher energies, the Standard Model gives an extremely economical formulation of the electroweak symmetry breaking in terms of the Higgs boson. It does not explain, however, the dynamical origin of the symmetry breaking, or why the Higgs boson should be light. One possibility is that the Higgs boson might be a bound state of a new strongly interacting sector slightly above the weak scale. Its composite nature would solve the hierarchy problem, for the quantum corrections to the Higgs mass will be saturated at the compositeness scale. Some models which realize this idea have been proposed.
Although the hadron and the Higgs sectors are realized at very different energy scales, the strong interacting dynamics have a number of similarities. The aim of this workshop is to gather together experts from lowenergy QCD and the BSM communities, in order to learn from each other about tools and methods to make progress in their respective fields.
