Probing AGN as Astrophysical Neutrino Sources with Millimeter-Wavelength Activity

In the past ten years, the IceCube South Pole Neutrino Observatory has revealed a neutrino sky in conflict with previous expectations from theory and multi-wavelength observations. While a diffuse flux of astrophysical neutrinos has been well established, certain analyses have found difficulty reconciling this intensity with expected neutrino source classes. Additionally, the discovery of the high-energy, transient neutrino source, TXS 0506+056, has drawn further attention to blazars, and the association of their activity with gamma-ray emission. More recently, the opacity of such environments to high-energy photons has been highlighted. Here, we discuss millimeter-wavelength observations of variable AGN as a robust tracer for neutrino activity. The relation of synchrotron emission at this wavelength to neutrino production is explored, and a first correlation of IceCube data with millimeter light curves from the Atacama Cosmology Telescope is discussed.