Transition radiation at radio frequencies from ultra-high energy neutrino-induced showers

Coherent radiation at radio frequencies from high-energy showers fully contained in a dense radio-transparent medium - like ice, salt or regolith - has been extensively investigated as a promising technique to search for ultra-high energy (UHE) neutrinos. Additional emission in the form of transition radiation may occur when a neutrino-induced shower produced close to the Earth surface emerges from the ground into atmospheric air. We present the first detailed evaluation of transition radiation from high-energy showers crossing the boundary between two different media. We found that transition radiation is sizable over a wide solid angle and coherent up to $\sim$ 1 GHz. These properties encourage further work to evaluate the potential of a large-aperture UHE neutrino experiment based on detection of transition radiation.