$CP$ violation for $B^+_{c}\rightarrow D_{(s)}^+\pi^+\pi^-$ in   Perturbative QCD
  In the perturbative QCD (PQCD) approach we study the direct $CP$ violation in $B^+_{c}\rightarrow D_{(s)}^+\rho^0(\omega) \rightarrow D_{(s)}^+\pi^+\pi^-$ via the $\rho-\omega$ mixing mechanism. We find that the $CP$ violation can be enhanced by $\rho-\omega$ mixing when the invariant masses of the $\pi^+\pi^-$ pairs are in the vicinity of the $\omega$ resonance. For the decay process $B^+_{c}\rightarrow D^+\rho^0(\omega) \rightarrow D^+\pi^+\pi^-$, the maximum $CP$ violation can reach 7.5 {\%}. 
Gang L\"u, Sheng-Tao Li, Yu-Ting Wang
hep-ph