Ultrahigh energy neutrinos from hidden-sector topological defects

We study topological defects (TD) in hidden (mirror) matter as possible sources of ultrahigh energy neutrinos. The hidden or 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 or 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 are not, due to oscillation into ordinary neutrinos. We show that oscillations of ultrahigh energy neutrinos can occur on a time scale less than the present 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.