Speaker
Description
In this talk we will study the implications on heavy hadron molecules (containing one constituent heavy quark) of heavy quark spin-flavor and chiral symmetries (together with unitarity). We start by studing the $D\pi$, $D\eta$ and $D_s \bar{K}$ scattering with $(I,J^P) = (1/2,0^+)$ quantum numbers. In this sector there appears the so far only known charmed non-strange scalar meson, namely $D^\ast_0(2400)$. We show that there are actually two poles in this energy region. With all the parameters involved in the amplitudes previously fixed, we predict the energy levels for the coupled-channel system in a finite volume, and find that they agree remarkably well with recent lattice QCD calculations. This successful description of the lattice data is regarded as a strong evidence for the two-pole structure of $D^\ast_0(2400)$. When the physical quark masses are considered, the poles are located at $\left(2105^{+6}_{-8}-i\,102^{+10}_{-12}\right)\ \text{MeV}$ and $\left(2451^{+36}_{-26}-i\,134^{+7}_{-8}\right)\ \text{MeV}$, being the largest
couplings to the $D\pi$ and $D_s\bar K$ channels, respectively. The higher pole is close to the $D_s\bar K$ threshold, and hence a threshold enhancement in the $D_s\bar K$ invariant mass distribution is to be expected. This predicted effect could be checked by future experiments.
The former amplitudes incorporate chiral symmetry, and hence they can be related with the ones in other strangeness-isospin sectors. Indeed, we also show that the lower pole belongs to the same $SU(3)$ multiplet as the $D_{s0}^*(2317)$ state. By means of heavy quark spin symmetry, predictions can also be given for $J=1$ sectors, involving a heavy vector meson. Further, due to heavy flavour symmetry, predictions for partners in the bottom sector are also given.
