  Cosmological inflation generates primordial density perturbations on all
scales, including those far too small to contribute to the cosmic microwave
background. At these scales, isolated ultracompact minihalos of dark matter can
form well before standard structure formation, if the perturbations have
sufficient amplitude. Minihalos affect pulsar timing data and are potentially
bright sources of gamma rays. The resulting constraints significantly extend
the observable window of inflation in the presence of cold dark matter,
coupling two of the key problems in modern cosmology.
