A new analysis has explored the decays of the D⁰ meson into pions and kaons, processes that are Cabibbo-suppressed. Researchers used factorization and isospin symmetry to quantify non-factorizable effects and the U-spin symmetry breaking required to explain the observed decay rates. This approach has established that corrections of the order of 50% are sufficient to describe these decays, a significant but not unexpected value in the realm of hadronic charm decays.

The study focused on the $D^0\to \pi^-\pi^+$, $D^0\to K^-K^+$ and $D^0\to K_{\rm S}^0K_{\rm S}^0$ decays. From the constraints imposed by the measured branching fractions, Standard Model (SM) predictions for the direct CP asymmetry in the $D^0\to K_{\rm S}^0K_{\rm S}^0$ decay have been derived. The results indicate that this asymmetry is, at most, at the per-mille level in the proposed benchmark scenario.

This prediction of a very small CP asymmetry in $D^0\to K_{\rm S}^0K_{\rm S}^0$ is crucial, as it provides clear motivation for future precision measurements. Detecting a CP asymmetry significantly larger than this per-mille level could signal the existence of new physics beyond the Standard Model, opening a window to as-yet unknown phenomena in particle physics.