= Cannibal phase of a decoupled sector
A massive decoupled sector enters a cannibal phase when its particles are nonrelativistic but rapid number-changing reactions maintain <chemical equilibrium> and <zero chemical potential from number-changing reactions>. Rest-mass <energy> released by $3\to2$ reactions heats the remaining particles, so the sector cools much more slowly than an isolated number-conserving nonrelativistic gas. The <temperature> laws follow directly from <cosmological entropy conservation>. An example is discussed in https://arxiv.org/abs/1602.04219[Cannibal Dark Matter].
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