Speaker
Description
The possible existence of hadrons with a more intricate nature than the traditional $q\bar{q}$ meson or $qqq$ baryon structures has been a central topic in hadron physics for decades. Interest in these "exotic" states escalated following the discovery of the narrow $\chi_{c1}(3872)$, located just below the $D^0\bar{D}^{*0}$ threshold. This was followed by the observation of several heavy hadrons, most notably the hidden-charm pentaquarks $P_c(4312)^+$, $P_c(4380)^+$, $P_c(4440)^+$, and $P_c(4457)^+$, as well as the more recent $T_{cc}(3875)^+$ tetraquark.
In this talk, I will present results from an extensive study of hidden-charm pentaquarks dynamically generated from meson-baryon interactions, covering all strangeness ($S$) and isospin ($I$) sectors. We compare two interaction models based on vector-meson exchange: one assuming $SU(4)$ flavor symmetry, and another that treats the heavy quark of the baryons as a spectator, thereby only imposing $SU(3)$ symmetry. The scattering amplitude is unitarized via the Bethe-Salpeter equation, a procedure requiring the regularization of the meson-baryon loop function.
Crucially, we show that standard schemes—such as dimensional regularization or a sharp cut-off—can produce unphysical artifacts in the scattering amplitude. To address this, we propose a new hybrid loop function that permits a natural disentanglement of physical states. This method provides consistent predictions across all sectors and reveals new pentaquark candidates with $S = -1, I = 1$, which were likely obscured by unphysical artifacts in the traditional schemes. Our results successfully reproduce six of the seven observed hidden-charm pentaquarks, providing a robust framework to stimulate further experimental searches in facilities worldwide.