Constraining Astrophysical Neutrino Flavor Composition from Leptonic Unitarity

Understand

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.