"We discuss two of the manifold ways in which phase
transitions in the early Universe can affect the dark matter abundance
today.  In the first part of the talk, we argue that phase transitions
can temporarily render dark matter unstable, allowing for efficient
depletion of its abundance.  In the second part of the talk, we show how
the bubble walls in a first order phase transition can act as a "filter"
for dark matter, allowing only a small fraction of them to enter, while
the bulk of the dark matter annihilates away efficiently."