Dark matter production in late time reheating

We estimate dark matter (DM) density for the Universe with a reheating temperature smaller than the mass of DM, assuming DM to be a weakly interacting massive particle. During the reheating process, an inflaton decays and releases high-energy particles, which are scattered inelastically by the thermal plasma and emit many particles. DMs are produced through these inelastic scattering processes and pair creation processes by high-energy particles. We properly take account of the Landau-Pomeranchuk-Migdal effect on inelastic processes and show that the resultant energy density of DM is much larger than that estimated in the literature and can be consistent with that observed when the mass of DM is larger than $O(100)\mathrm{GeV}$.

Figure 1

Sample diagram describing an elastic scattering.

Figure 2

Sample diagram describing an inelastic scattering.

Figure 3

Exclusion plot in a scenario with low reheating temperature. We assume that the mass of the inflaton $m_{\varphi }$ is $10^{12}\mathrm{GeV}$ and that the branching of inflaton decay into DM is 1 (left panel) and 0.02 (right panel). We also assume ${\alpha }_{\mathrm{DM}}=\alpha$. The abundance of DM produced from thermal production (${\mathrm{\Omega }}_{\text{DM}}^{\text{th}}{h}^2$), direct decay of inflaton (${\mathrm{\Omega }}_{\text{DM}}^{\text{dir}}{h}^2$), and inelastic scatterings (${\mathrm{\Omega }}_{\text{DM}}^{\text{sca}}{h}^2$) is larger than that observed in the green (dark gray), red (light gray), and blue (middle gray) shaded regions, respectively. The striped region are $T_{\text{RH}}>m_{\text{DM}}/10$, in which DM is produced only thermally. The abundance of DM is less than that observed above the blue dashed line due to its annihilation. Here, we have assumed that the annihilation of DM is efficient and its cross section is $10^{-2}{m}_{\text{DM}}^{-2}$. The red dotted lines represent the reheating temperature below which ${\mathrm{\Omega }}_{\text{DM}}^{\text{sca}}{h}^2$ is overestimated.

Figure 4

Same as Fig. 3, but assuming the mass of the inflaton to be $10^{15}\mathrm{GeV}$.