  Lusignoli and Vignati have recently pointed out that it is in principle
possible to directly detect the cosmic antineutrino background by using the
rather stable isotope holmium-163 as a target, which can decay into
dysprosium-163 via electron capture (EC) with a very small energy release. In
this paper we calculate the rate of the relic antineutrino capture on
holmium-163 nuclei against the corresponding EC decay rate by taking account of
different neutrino mass hierarchies and reasonable values of theta_13. We show
that such flavor effects are appreciable and even important in some cases, and
stress that a calorimetric measurement of the cosmic antineutrino background
might be feasible in the far future.
