"Light Dark Matter from Boltzmann Factors"

 

 

 

he observed dark matter abundance can be explained by a thermal relic that annihilates in the early universe with a weak scale cross section, suggesting a weak scale mass for dark matter.   However, dark matter annihilations may require finite temperature, implying that the final dark matter abundance is exponentially enhanced by a Boltzmann factor.  This possibility points to dark matter exponentially lighter than the weak scale.  I will highlight examples of light hidden sector dark matter where finite temperature is required, including scenarios where the dark matter abundance is set by forbidden annihilations, coannihilations, and inelastic scattering.