Probing MeV dark matter at low-energy e+e- colliders.

It has been suggested that the pair annihilation of dark matter particles chi with mass between 0.5 and 20 MeV into e+e- pairs could be responsible for the excess flux (detected by the INTEGRAL satellite) of 511 keV photons coming from the central region of our Galaxy. The simplest way to achieve the required cross section while respecting existing constraints is to introduce a new vector boson U with mass M(U) below a few hundred MeV.

Production of massive stable particles in inflaton decay.

We point out that inflaton decays can be a copious source of stable or long-lived particles chi with mass exceeding the reheat temperature T(R) but less than half the inflaton mass. Once higher order processes are included, this statement is true for any chi particle with renormalizable (gauge or Yukawa) interactions. This contribution to the chi density often exceeds the contribution from thermal chi production, leading to significantly stronger constraints on model parameters than those resulting from thermal chi production alone, particularly in models containing stable charged particles.