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The ANITA collaboration have reported observation of two anomalous eventsthat appear to be $\varepsilon_{\rm cr} \approx 0.6$ EeV cosmic ray showersemerging from the Earth with exit angles of $27^\circ$ and $35^\circ$,respectively. While EeV-scale upgoing showers have been anticipated as a resultof astrophysical tau neutrinos converting to tau leptons during Earth passage,the observed exit angles are much steeper than expected in Standard Model (SM)scenarios. Indeed, under conservative extrapolations of the SM interactions,there is no particle that can propagate through the Earth with probability $p >10^{-6}$ at these energies and exit angles. We explore here whether "beyond theStandard Model" (BSM) particles are required to explain the ANITA events, ifcorrectly interpreted, and conclude that they are. Seeking confirmation orrefutation of the physical phenomenon of sub-EeV Earth-emergent cosmic rays indata from other facilities, we find support for the reality of the ANITAevents, and three candidate analog events, among the Extremely High EnergyNorthern Track neutrinos of the IceCube Neutrino Observatory. Properties of theimplied BSM particle are anticipated, at least in part, by those predicted forthe "stau" slepton ($\tilde{\tau}_R$) in some supersymmetric models of thefundamental interactions, wherein the stau manifests as the next-to-lowest masssupersymmetric partner particle.

The ANITA Anomalous Events as Signatures of a Beyond Standard Model Particle, and Supporting Observations from IceCube