Interplay of super-WIMP and freeze-in production of dark matter

Nonthermalized dark matter is a cosmologically valid alternative to the paradigm of weakly interacting massive particles. For dark matter belonging to a $Z_2$-odd sector that contains in addition a thermalized mediator particle, dark matter production proceeds, in general, via both the freeze-in and super-WIMP mechanism. We highlight their interplay and emphasize the connection to long-lived particles at colliders. For the explicit example of a colored $t$-channel mediator model we map out the entire accessible parameter space, cornered by bounds from the LHC, big bang nucleosynthesis and Lyman-$\alpha$ forest observations, respectively. We discuss prospects for the HL- and HE-LHC.

Figure 1

Dark matter coupling strength ${\lambda }_{\chi }$ providing $\mathrm{\Omega }{h}^2\simeq 0.12$ as a function of $m_{\chi }$ (green solid curve) for $\mathrm{\Delta }m=2.5\mathrm{TeV}$ (left) and 100 TeV (right). The green shaded band provides an estimate of the uncertainties due to the regularization of divergent diagrams: the upper boundary is obtained from leaving out the respective diagrams while the lower boundary represents a looser cut (see text for details). The purple and red shaded regions denote 95% CL exclusions from Lyman-$\alpha$ and BBN bounds, respectively. The cyan dotted curves show contours of constant mediator decay length, while the blue dotted curve shows the projected sensitivity of the 27 TeV HE-LHC.

Figure 2

Cosmologically viable parameter space ($\mathrm{\Omega }{h}^2\simeq 0.12$) in the $m_{\chi }\text{‐}\mathrm{\Delta }m$ plane displayed logarithmically (left) and linearly (right) in $m_{\chi }$. The thin green lines denote contours of constant coupling strength ${\lambda }_{\chi }$. The black thick line marks the over-closure bound while the black dashed (right panel only) and dotted lines denote the contours where $f^{\mathrm{sW}}=50\%$ and 10%, respectively. The red and purple shaded regions are excluded by bounds from BBN and the Lyman-$\alpha$ forest. The blue shaded region is excluded by $R$-hadron searches at the 13 TeV LHC. The dashed and dotted blue curves denote the respective projection for the 14 TeV HL-LHC and 27 TeV HE-LHC, respectively.