Speaker
Description
In the last decade, the IceCube Collaboration reported the existence of an astrophysical neutrino flux of ultra-high energy. In this extreme energy limit, the neutrino-nucleon interaction does occur in a kinematic domain inaccessible to the present terrestrial colliders. This situation is especially relevant when we consider the squared of the transferred momentum, Q², which can assume values above the squared of the mass of the W boson. Also, the Bjorken X variable, which is the fraction of the nucleon momentum carried by a parton, can reach values of the order of $10⁻⁶$ or $10⁻⁷$. Indeed, the extrapolation of parton density functions (PDFs) to this kinematic region considering only linear QCD dynamics results in intense growth of PDFs, which in the extreme limit implies violations of unitarity in the hadronic cross-sections. On the other hand, predictions to the hadronic interactions based on the Froissart bound are known to successfully describe the hadron-hadron and photon-hadron interaction data and imposes limits on the structure-function $F_{2}(X, Q^{2})$ when $x\rightarrow 0$. This assures the conservation of the unitarity of such cross-sections, which are limited to growing at a maximum of $ln^{2}(S)$. Considering the neutrino-nucleon interaction, the Froissart bound constrains the increase of the cross-section to $ln^{3}(E_{\nu})$. All these features are incorporated in the BBMT model for the neutrino-nucleon interaction. In this work, we investigate the consequences of the BBMT model at the energies of the High-Energy Sample of Events at IceCube (HESE) and above. We also compare it with the predictions from the standard CT14 model. We study in detail the impacts of such dynamics on the angular dependence of the neutrino absorption by the Earth. In comparison with the predictions from linear QCD dynamics, we found that the impact of the Froissart bound is of an order of $10\%$ and is sensitive to the incoming neutrino direction. Also, we investigate its consequences on the averaged inelasticity, $Y(E_{\nu})=1-E_{\mu}/E_{\nu}$, of the neutrino interactions at at ultrahigh neutrino energies. Our results point that the impact on $Y(E_{\nu})$ is of the order of only $5\%$ for muon tracks and electromagnetic showers, but can reach $25\%$ for the hadronic cascades. These effects surely play some role in the description of the present data and will be more relevant at the planned extension to the IceCube-Gen2. Finally, we include in our analysis the hypothesis of the existence of the so-called Super-Glashow neutrino fluxes, which are peaked at energies above the Glashow resonance and are more likely to generate events at extreme energies than the usual single power-like astrophysical neutrino fluxes. In comparison with the CT14 predictions, our results demonstrate that the BBMT model implies distortions in the energy spectrum of events of the order of $20\%$ at the peak of the distribution.
