Hunting Down Massless Dark Photons in Kaon Physics

Area of Science:

• Particle Physics
• Beyond Standard Model Physics
• High Energy Physics

Background:

• Direct interactions of massless dark photons with standard model particles are absent, necessitating exploration of alternative coupling mechanisms.
• Kinetic mixing is a common motivation for dark photon searches, but this study focuses on higher-dimensional operators for massless dark photons.

Purpose of the Study:

• To investigate the impact of flavor-changing magnetic-dipole couplings of massless dark photons in kaon physics.
• To calculate the branching ratio for the rare decay K+ → π+π0γ[over ¯] considering these couplings.

Main Methods:

• A simplified-model approach was employed to analyze the interactions.
• The chiral quark model was used to evaluate the hadronic matrix element for the decay.
• Effects on K0–K[over ¯]0 mixing were also considered.

Main Results:

• Branching ratios for K+ → π+π0γ[over ¯] up to O(10^{-7}) are found to be allowed.
• The allowed branching ratios depend on the dark-sector masses and coupling strengths.
• The invisible system γ[over ¯] can be detected in experiments like NA62 at CERN.

Conclusions:

• Flavor-changing magnetic-dipole couplings of massless dark photons can lead to observable effects in rare kaon decays.
• The predicted branching ratios are significant enough to be probed by current and future experiments searching for rare K+ decays.