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The Antarctic Impulsive Transient Antenna (ANITA) experiment has observed twoair shower events with energy $\sim 500~{\rm PeV}$ emerging from the Earth withexit angles $\sim 30^\circ$ above the horizon. As was immediately noted by theANITA Collaboration, these events (in principle) could originate in theatmospheric decay of an upgoing $\tau$-lepton produced through a chargedcurrent interaction of a $\nu_\tau$ inside the Earth. However, the relativelysteep arrival angles of these perplexing events create tension with thestandard model (SM) neutrino-nucleon interaction cross section. Deepening theconundrum, the IceCube neutrino telescope and the Pierre Auger Observatory withsubstantially larger exposures to cosmic $\nu_\tau$'s in this energy range havenot observed any events. This lack of observation implies that the messengerparticle (MP) giving rise to ANITA events must produce an air shower event rateat least a factor of 40 larger than that produced by a flux of $\tau$-neutrinosto avoid conflicts with the upper limits reported by the IceCube and the PierreAuger collaborations. In addition, the sensitivity of ANITA to MP-inducedevents must be comparable to or larger than those of IceCube and Auger to avoidconflict with the non-observation of any signal at these facilities. Beyond SMinterpretations of ANITA events can be classified according to whether the MPs:(i) live inside the Earth, (ii) originate in neutrino-nucleon collisions insidethe Earth, (iii) come from cosmological distances. In this communication weinvestigate the positive and negative facets of these three classes of models.

The pros and cons of beyond standard model interpretations of ANITA events