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The existence of stable multiquarks made of heavy quarks and antiquarks is discussed in the framework of potential models. It is stressed that the few-body problem should be handled seriously and accurately. No bound state is found within the current models. But resonances are likely present in the spectrum above the lowest threshold., Comment: Contribution to the 8th Asian-Pacific Few-Body Conference, Kanazawa (Japan), March 2021, to appear in a special issue of Few-Body Systems

We present a selection of topics with an interplay of hadron and few-body physics. This includes few-nucleon systems, light hypernuclei and quark dynamics for baryons and multiquarks. It is stressed that standard quark models predict very few stable multiquarks., 17 pages, 2 figures, invited contribution to the special issue of Few Body Systems on Hadrons, 1 ref. added

International audience; The parity-violating neutron spin rotation in He4 is studied at vanishing incident neutron energy limit. Calculations have been realized by solving five-body Faddeev-Yakubovsky equations in configuration space employing modern strong-interaction Hamiltonian based on chiral perturbation theory including three-nucleon force. Parity-violating nucleon-nucleon interaction of the Desplanques, Donoghue, and Holstein model is employed. An implication of the recent theoretical large-Nc estimation of weak couplings [Phillips , Phys. Rev. Lett. 114, 062301 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.062301] is also discussed.

We outline the most important results regarding the stability of doubly heavy tetraquarks $QQ\bar q\bar q$ with an adequate treatment of the four-body dynamics. We consider both color-mixing and spin-dependent effects. Our results are straightforwardly applied to the case of all-heavy tetraquarks $QQ\bar Q\bar Q$. We conclude that the stability is favored in the limit $M_Q/m_q \gg 1$ pointing to the stability of the $bb\bar u\bar d$ state and the instability of all-heavy tetraquarks., To appear in the Proc. of the Workshop "XIII International Conference on Beauty, Charm and Hyperon Hadrons", Peniche (Portugal), June 17-23, 2018. To be published by IOP Conference Series

Few and many-body systems usually feature interesting and novel behaviors compared with their counterparts in three dimensions. On one hand, low dimensional physics presents challenges due to strong interactions and divergences in the perturbation theory; On the other hand, there exist powerful theoretical tools such as the renormalization group and the Bethe ansatz. In this thesis, I discuss two examples: three interacting bosons in two dimensions and interacting bosons/fermions in one dimension. In both examples, there are intraspecies repulsion as well as interspecies attraction, producing a rich spectrum of phenomena. In the former example, a universal curve of three-body binding energies versus scattering lengths is obtained efficiently by evolving a matrix renormalization group equation. In the latter example, exact solutions for the BCS-BEC crossover are obtained and the unexpected robust features in their excitation spectra are explained by a comprehensive semiclassical analysis.