Hunting down massless dark photons in kaon physics

Understand

If dark photons are massless, they couple to standard-model particles only via higher dimensional operators, while the kinetic mixing with photons, which motivates most of the current experimental searches, is absent.

• We consider the effect of possible flavor-changing magnetic-dipole couplings of massless dark photons in kaon physics.
• In particular, we study the branching ratio for the process $K^+\rightarrow \pi^+\pi^0 \bar \gamma$ with a simplified-model approach, assuming the chiral quark model to evaluate the hadronic matrix element.
• Possible effects in the $K^0$-$\bar K^0$ mixing are taken into account.