  We study Topological Defects (TD) in hidden (mirror) matter as possible
sources of ultra-high energy neutrinos. The hidden/mirror and ordinary matter
are assumed to interact very weakly through gravity or superheavy particles. An
inflationary scenario is outlined in which superheavy defects are formed in
hidden/mirror matter (and not in ordinary matter), and at the same time the
density of mirror matter produced at the end of inflation is much smaller than
that of ordinary matter. Superheavy particles produced by hidden-sector TD and
the products of their decays are all sterile in our world. Only mirror
neutrinos oscillate into ordinary neutrinos. We show that oscillations with
maximal mixing of neutrinos from both worlds are possible and that values of
$\Delta m^2$, needed for for solution of solar-neutrino and
atmospheric-neutrino problems, allow the oscillation of ultra-high energy
neutrinos on a timescale of the age of the Universe. A model of mass-degenerate
visible and mirror neutrinos with maximal mixing is constructed. Constraints on
UHE neutrino fluxes are obtained. The estimated fluxes can be 3 orders of
magnitude higher than those from ordinary matter. Detection of these fluxes is
briefly discussed.
