Boosted Dark Matter and its implications for the features in IceCube HESE data

We study the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector. Such events would be observationally indistinguishable from neutral current deep-inelastic scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event data (HESE), we focus on particular boosted dark matter ($\chi$) related realizations of this premise. Here, $\chi$ is assumed to be much lighter than, and the result of, the slow decay of a massive scalar ($\phi$) which constitutes a major fraction of the Universe's dark matter. We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample. These features include a) the paucity of events beyond $\sim 2$ PeV b) a spectral feature resembling a dip or a spectral change in the 400 TeV--1 PeV region and c) an excess in the $50-100$ TeV region. We consider two different boosted DM scenarios, and determine the allowed mass ranges and couplings for four different types of mediators (scalar, pseudoscalar, vector and axial-vector) which could connect the standard and dark sectors. We consider constraints from gamma-ray observations and collider searches. We find that the gamma-ray observations provide the most restrictive constraints, disfavouring the $1\sigma$ allowed parameter space from IC fits, while still being consistent with the $3\sigma$ allowed region. We also test our proposal and its implications against IC's recent six-year through-going muon track data.