We perform a unitary coupled channel study of the interaction of the $D^{*+}{D}^0,D^{*0}{D}^{+}$ channels and find a state barely bound, very close to isospin $I=0$. We take the experimental mass as input and obtain the width of the state and the $D^0{D}^0{\pi }^{+}$ mass distribution. When the mass of the $T_{cc}$ state quoted in the experimental paper from raw data is used, the width obtained is of the order of the 80 keV, small compared to the value given in that work. Yet, when the mass obtained in an analysis of the data considering the experimental resolution is taken, the width obtained is about 43 keV and both the width and the $D^0{D}^0{\pi }^{+}$ mass distribution are in remarkable agreement with the results obtained in that latter analysis.

In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.

The hidden-charm pentaquark $$P_c(4450)$$ observed recently by the LHCb collaboration may be of molecular nature, as advocated by some unitary approaches t

A study of the meson-baryon interaction in the $S=-1$ sector is performed, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The model is constrained by a large set of experimental data, paying special attention to processes that are sensitive to the NLO contributions, such as the $K^{-}p\to K^{+}{\mathrm{\Xi }}^{-},K^0{\mathrm{\Xi }}^0$ reactions. The consideration of additional cross sections in single isospin channels, $K^{-}p\to \eta \mathrm{\Lambda },\eta \mathrm{\Sigma }$, has been found to provide NLO low-energy constants of rather similar size. The stability of these constants has also been tested by the inclusion of explicit resonant terms. Predictions for new isospin filtering processes, like the $I=1K_L^{0}p\to K^{+}{\mathrm{\Xi }}^0$ reaction that could be measured at the proposed secondary $K_L^0$ beam at Jlab, or the weak decay of the ${\mathrm{\Lambda }}_b$ into a $J/\mathrm{\Psi }$ and different meson-baryon pairs in $I=0$, available at LHCb, are presented. The measurement of such reactions would put valuable constraints on the chiral models describing the $S=-1$ meson-baryon interaction.