Probing new physics with high-multiplicity events: UHE neutrinos at air-shower detector arrays

Semi-classical processes such as production and decay of electroweak sphaleron in the Standard Model and also microscopic black hole in low scale gravity scenario typically involve large number of particles in final states. These large multiplicities can be distinctively seen in collisions of Ultra-high-energy (UHE) neutrinos with $E_{\nu }\ge {10}^9\text{ GeV}$ and nucleons in the atmosphere of the Earth. Focusing on air-shower detector array experiments including Telescope Array Experiment (TA), Pierre-Auger Observatory (Auger), we propose strategic ways to discover and analyze such events.