Two-component flux explanation for the high energy neutrino events at IceCube

Understanding the spectral and flavor composition of the astrophysical neutrino flux responsible for the recently observed ultrahigh-energy events at IceCube is of great importance for both astrophysics and particle physics. We perform a statistical likelihood analysis to the three-year IceCube data and derive the allowed range of the spectral index and flux normalization for various well-motivated physical flavor compositions at the source. While most of the existing analyses so far assume the flavor composition of the neutrinos at an astrophysical source to be (1:2:0), it seems rather unnatural to assume only one type of source, once we recognize the possibility of at least two physical sources. Bearing this in mind, we entertain the possibility of a two-component source for the analysis of IceCube data. It appears that our two-component hypothesis explains some key features of the data better than a single-component scenario; i.e. it addresses the apparent energy gap between 400 TeV and about 1 PeV and easily accommodates the observed track-to-shower ratio. Given the extreme importance of the flavor composition for the correct interpretation of the underlying astrophysical processes as well as for the ramification for particle physics, this two-component flux should be tested as more data is accumulated.