Heavy Neutral Leptons via Axionlike Particles at Neutrino Facilities

Area of Science:

• Particle Physics
• Cosmology
• Astroparticle Physics

Background:

• Heavy neutral leptons (HNLs) are hypothetical particles proposed to explain neutrino masses.
• Current models often assume HNLs interact via standard weak interactions.
• Fixed-target experiments are a key avenue for HNL detection.

Purpose of the Study:

• To explore novel production mechanisms for HNLs beyond standard weak interactions.
• To investigate the role of a richer dark sector, including axionlike particles (ALPs), in HNL production.
• To assess the sensitivity of experiments like DUNE to these alternative HNL production scenarios.

Main Methods:

• Postulating a dark sector containing an ALP that decays into HNLs.
• Analyzing the implications of ALP-hadron mixing on HNL production.
• Comparing HNL production via neutral meson decays versus charged meson decays.

Main Results:

• HNL production can be dominated by neutral meson decays (e.g., π⁰, η) when mediated by ALPs.
• This mechanism deviates significantly from standard weak interaction predictions.
• The production and decay physics of HNLs can be decoupled in this scenario.

Conclusions:

• Experiments like DUNE may detect HNLs too weakly coupled for standard weak production.
• This provides a complementary search strategy for HNLs relevant to neutrino mass models.
• The study highlights the importance of considering extended dark sector models for HNL phenomenology.