Signatures of cosmic tau – neutrinos

The importance and signatures of cosmic tau–(anti)neutrinos have been studied for upward– and downward–going µ − + µ + and hadronic shower event rates relevant for present and future underground water or ice detectors, utilizing the unique and reliable ultrasmall–x predictions of the dynamical (radiative) parton model. Cosmic ν τ + ¯ ν τ fluxes, together with their associated τ − + τ + fluxes, enhance sizeably the upward–going µ − +µ + event rates initiated by ν µ + ¯ ν µ fluxes. The coupled transport equations for the upward–going (−) ν τ flux traversing the Earth imply an enhancement of the attenuated and regenerated (−) ν τ flux typically around 10 4 − 10 5 GeV with respect to the initial cosmic flux which turns out to be smaller than obtained so far, in particular for flatter initial cosmic fluxes behaving like E −1 ν. Downward–going µ − + µ + events and in particular the background–free and unique hadronic 'double bang' and 'lollipop' events allow to test downward–going cosmic ν τ + ¯ ν τ fluxes up to about 10 9 GeV.