The Lancet Planetary Health, cilt.8, sa.10, 2024 (SCI-Expanded)
The mass difference of $c$ and $u$ quarks is similar to the energy needed to excite gluonic degrees of freedom in strong QCD. This underpins the degeneracy of $D$ and a recently observed candidate hybrid excitation of the $\pi$ at$\sim 1.8$GeV and may generate a strong analogue of Penguin mixing together with a measurable CP-violation in $D$ and $D_s$ decays.