Enhanced charm CP asymmetries from final state interactions

We show that final state interactions (FSI) within a CPT invariant two-channel framework can enhance the charge-parity (CP) violation difference between $D^0\to\pi^-\pi^+$ and $D^0\to K^-K^+$ decays up to the current experimental value. This result relies upon: (i) the dominant tree level diagram, (ii) the well-known experimental values for the $D^ 0\to\pi^-\pi^+$ and $D^ 0\to K^-K^+$ branching ratios, and (iii) the $\pi\pi \to \pi\pi$ and $\pi\pi \to K K$ scattering data to extract the strong phase difference and inelasticity. Based on well-grounded theoretical properties, we find the sign and bulk value of the $\Delta A_{CP}$ and $A_{CP}(D^0 \to \pi^-\pi^+)$ recently observed by the LHCb Collaboration.