$P_c(4312)^+$, $P_c(4380)^+$, and $P_c(4457)^+$ as novel kinematical effect.

Understanding the nature of the hidden charm pentaquark(like) signals in the LHCb data for $\Lambda_b^0\to J/\psi p K^-$ is a central problem of hadron spectroscopy. We propose a scenario completely different from previous ones such as hadron molecules and compact pentaquarks. We identify relevant double triangle mechanisms that cause double triangle singularities. This novel kinematical effect significantly enhances $\Sigma_c^{(*)}\bar{D}^{(*)}$ threshold cusps. Then we demonstrate that the double triangle amplitudes reproduce the peak structures of $P_c(4312)^+$, $P_c(4380)^+$, and $P_c(4457)^+$ in the LHCb data, through an interference with other common mechanisms. Only the $P_c(4440)^+$ peak is due to a resonance with width and strength significantly smaller than previously estimated. $P_c$ signals are expected in other processes and the proposed model (partly) explains the current data such as: the GlueX $J/\psi$ photoproduction data with no $P_c$ signals; the LHCb $\Lambda_b^0\to J/\psi p \pi^-$ data with a possible signal only from $P_c(4440)^+$.