Solar System constraints and signatures for dark-matter candidates

We show that if our galactic halo were to consist of scalar or Dirac neutrinos with mass greater than 12 GeV, capture by the Earth and subsequent annihilation would yield a large flux of neutrinos at the surface which could be seen in proton-decay detectors. The luminosity of Uranus provides comparable constraints. Capture in the Sun can yield supplementary information, with detectable signals possible for masses as low as 6 GeV for both Dirac and Majorana neutrinos, scalar neutrinos, and photinos. We discuss in detail the question of evaporation, on which our results and others depend sensitively. We suggest one method of approximating evaporation rates from the Earth and Sun and discuss potential problems with earlier estimates. Finally, we describe how particles which avoid these constraints may still be detectable by bolometric neutrino detectors and isolate a new method to remove backgrounds to this signal in such detectors.