  Astronomical observations from small galaxies to the largest scales in the
universe can be consistently explained by the simple idea of dark matter. The
nature of dark matter is however still unknown. Empirically it cannot be any of
the known particles, and many theories postulate it as a new elementary
particle. Searches for dark matter particles are under way: production at
high-energy accelerators, direct detection through dark matter-nucleus
scattering, indirect detection through cosmic rays, gamma rays, or effects on
stars. Particle dark matter searches rely on observing an excess of events
above background, and a lot of controversies have arisen over the origin of
observed excesses. With the new high-quality cosmic ray measurements from the
AMS-02 experiment, the major uncertainty in modeling cosmic ray fluxes is in
the nuclear physics cross sections for spallation and fragmentation of cosmic
rays off interstellar hydrogen and helium. The understanding of direct
detection backgrounds is limited by poor knowledge of cosmic ray activation in
detector materials, with order of magnitude differences between simulation
codes. A scarcity of data on nucleon spin densities blurs the connection
between dark matter theory and experiments. What is needed, ideally, are more
and better measurements of spallation cross sections relevant to cosmic rays
and cosmogenic activation, and data on the nucleon spin densities in nuclei.
