Cosmic Neutrino Flavor Ratios with Broken ${\nu }_{\mu }-{\nu }_{\tau }$ Symmetry

Abstract

Reactor neutrino experiments have now observed a nonzero value for ${\theta }_{13}$ at $5\sigma$, and global fits to data imply a nonzero value above $10\sigma$. Nonzero values for ${\theta }_{13}$ and/or ${\theta }_{32}-\pi /4$ break a ${\nu }_{\mu }-{\nu }_{\tau }$ symmetry, which has qualitative as well as quantitative implications for the time-evolution of neutrino flavors. In particular, the large-distance flavor evolution matrix, non-invertible with ${\nu }_{\mu }-{\nu }_{\tau }$ symmetry, is now invertible. This means that measurements of neutrino flavor ratios at Earth can now be inverted to directly reveal the flavor ratios injected at cosmically distant sources. With the updated values of the three neutrino mixing angles, we obtain the inverted large-distance evolution matrix and use it to derive several phenomenological relations between the injection flavor ratios and the observable ratios at Earth. Taking the three popular injection models as examples, we also exhibit the shift of Earthly observed flavor ratios from the corresponding values in the case with ${\nu }_{\mu }-{\nu }_{\tau }$ symmetry.

8 pages, 1 figure, v2: version to appear in PLB

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• Aspects of the Flavor Triangle for Cosmic Neutrino Propagation
• Constraining Astrophysical Neutrino Flavor Composition from Leptonic Unitarity
• Tau Appearance from High-Energy Neutrino Interactions
• The flavor composition of ultra-high-energy cosmic neutrinos: measurement forecasts for in-ice radio-based EeV neutrino telescopes
• Two-detector flavor sensitivity to ultra-high-energy cosmic neutrinos
• Energy-dependent flavor ratios, cascade/track spectrum tension and high-energy neutrinos from magnetospheres of supermassive black holes
• Aspects of astrophysical particle production and beyond the Standard Model phenomenology