Thermal effects on the absorption of ultra-high energy neutrinos by the   cosmic neutrino background
  We use the formalism of finite-temperature field theory to study the interactions of ultra-high energy (UHE) cosmic neutrinos with the background of relic neutrinos and to derive general expressions for the UHE neutrino transmission probability. This approach allows us to take into account the thermal effects introduced by the momentum distribution of the relic neutrinos. We compare our results with the approximate expressions existing in the literature and discuss the influence of thermal effects on the absorption dips in the context of favoured neutrino mass schemes, as well as in the case of clustered relic neutrinos. 
J. C. D'Olivo, L. Nellen, S. Sahu and V. Van Elewyck