Density matrix calculation of the dark matter abundance in the Higgs induced right-handed neutrino mixing model

Understand

We present new results on the calculation of the dark matter relic abundance within the Higgs induced right-handed (RH) neutrino mixing model, solving the associated density matrix equation.

• For a benchmark value of the dark matter mass $M_{\rm DM} = 220\,{\rm TeV}$, we show the evolution of the abundance and how this depends on reheat temperature, dark matter lifetime and source RH neutrino mass $M_{\rm S}$, with the assumption $M_{\rm S} < M_{\rm DM}$.
• We compare the results with those obtained within the Landau-Zener approximation, showing that the latter largely overestimates the final abundance giving some analytical insight.
• However, we also notice that since in the density matrix formalism the production is non-resonant, this allows source RH neutrino masses below the W boson mass, making dark matter more stable at large mass values.