arXiv subjects
Publications and source records attributed to Ou Zhang.
Positivity constraints on the LECs of $\cO(p^6)$ $χ$PT lagrangian are discussed. We demonstrate that the constraints are automatically satisfied inside the Mandelstam triangle for $ππ$ scatterings, when $N_C$ is large. Numerical tests are made in the $N_C=3$ case, and it is found that these constraints are also well respected.
An analysis including most recent Belle data on X(3872) is performed, using coupled channel Flatté formula. A third sheet pole close to but \textit{below} $D^0D^{*0}$ threshold is found, besides the bound state/virtual state pole discussed in previous literature. The co-existence of two poles near the $D^0D^{*0}$ threshold indicates that the X(3872) may be of ordinary $c\bar c$ $2 ^3P_1$ state origin, distorted by strong coupled channel effects. The latter manifests itself as a molecular bound state (or a virtual state).
We estimate the di-photon coupling of $f_0(600)$, $f_0(980)$ and $f_2(1270)$ resonances in a coupled channel dispersive approach. The $f_0(600)$ di-photon coupling is also reinvestigated using a single channel $T$ matrix for $ππ$ scattering with better analyticity property, and it is found to be significantly smaller than that of a $\bar qq$ state. Especially we also estimate the di-photon coupling of the third sheet pole located near $\bar KK$ threshold, denoted as $f_0^{III}(980)$. It is argued that this third sheet pole may be originated from a coupled channel Breit-Wigner description of the $f_0(980)$ resonance.