New Limits on CPT-Symmetry Violation in Charm Mesons

Neutral flavour meson oscillations are a fascinating quantum phenomenon that allows for high-precision tests of fundamental symmetries, including CPT invariance. In this contribution, we present the methodology for testing CPT violation in neutral flavour meson systems, with particular emphasis on the charm sector. We report the recently established constraints on CPT-violating effects, derived from a reinterpretation of the LHCb measurement of the time-dependent asymmetry in the Cabibbo-favoured decays $D^0 \to K^- π^+$ and $\bar{D}^0 \to K^+ π^-$. Our results improve the previous bounds by the FOCUS experiment by approximately two orders of magnitude. We also discuss prospects for tests of CPT invariance, including the Standard Model Extension framework.