We propose new physical processes based on the axial vector anomaly and described by the Wess-Zumino-Witten term that couples the photon, $Z$-boson, and the $\omega$-meson. The interaction takes the form of a pseudo-Chern-Simons term, $\sim {ϵ}_{\mu \nu \rho \sigma }{\omega }^{\mu }{Z}^{\nu }{F}^{\rho \sigma }$. This term induces neutrino-photon interactions at finite baryon density via the coupling of the $Z$-boson to neutrinos. These interactions may be detectable in various laboratory and astrophysical arenas. The new interactions may account for the excess observed at the Fermilab Booster Neutrino Experiment MiniBooNE. They also produce a competitive contribution to neutron star cooling at temperatures $\gtrsim {10}^9\mathrm{K}$. These processes and related axion-photon interactions at finite baryon density appear to be relevant in many astrophysical regimes.

• Received 19 August 2007

DOI:https://doi.org/10.1103/PhysRevLett.99.261601