  We present a new paradigm for the production of dark-matter particles called
the spontaneous freeze out, in which the decoupling from the thermal bath is
enforced by the sudden increase of the dark-matter mass, due to the spontaneous
breaking of some global symmetry rather than by the slow decrease of the
temperature. We study the details of the spontaneous freeze out mechanism using
a simple toy model and analyze the phenomenology of our scenario. We show that
in order to obtain the correct relic abundance, the annihilation cross section
of dark-matter particles into Standard-Model states has to be typically much
larger than in the case of a constant-mass thermal dark-matter candidate. We
present a string theory model in which such a scenario takes place naturally.
