Low-mass boson dark matter particles produced after the Big Bang

form a classical field and/or topological defects. Effects produced

by the interaction of ordinary matter with dark matter may be first

power in the underlying interaction strength rather than the second

power. This may give a big advantage, since the dark matter

interaction constant is extremely small. Limits on certain types of

dark matter have been improved up to 15 orders of magnitude. New

experiments are proposed.