Constraining Astrophysical Neutrino Flavor Composition from Leptonic Unitarity

Abstract

The recent IceCube observation of ultra-high-energy astrophysical neutrinos has begun the era of neutrino astronomy. In this work, using the unitarity of leptonic mixing matrix, we derive nontrivial unitarity constraints on the flavor composition of astrophysical neutrinos detected by IceCube. Applying leptonic unitarity triangles, we deduce these unitarity bounds from geometrical conditions, such as triangular inequalities. These new bounds generally hold for three flavor neutrinos, and are independent of any experimental input or the pattern of leptonic mixing. We apply our unitarity bounds to derive general constraints on the flavor compositions for three types of astrophysical neutrino sources (and their general mixture), and compare them with the IceCube measurements. Furthermore, we prove that for any sources without ${\nu }_{\tau }$ neutrinos, a detected ${\nu }_{\mu }$ flux ratio $<1/4$ will require the initial flavor composition with more ${\nu }_e$ neutrinos than ${\nu }_{\mu }$ neutrinos.

JCAP Final Version. 24pp. Only minor refinements, references added

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Cited by in corpus (8)

• Testing decay of astrophysical neutrinos with incomplete information
• Spectral analysis of the high-energy IceCube neutrinos
• Inferring the flavor of high-energy astrophysical neutrinos at their sources
• High-energy neutrino fluxes and flavor ratio in the Earth's atmosphere
• Aspects of the Flavor Triangle for Cosmic Neutrino Propagation
• Probing New Physics at Future Tau Neutrino Telescopes
• 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