Scrutinizing Fermionic Dark Matter in Scotogenic Model with Low Reheating Temperature

Abstract

The scotogenic model provides a minimal and elegant framework that simultaneously explains neutrino masses and accommodates a viable dark matter (DM) candidate. In this work, we investigate the phenomenology of fermionic DM in the scotogenic model, with a particular emphasis on the effects of a non-standard cosmological history characterized by a low reheating temperature. We demonstrate that entropy injection from inflaton decay can significantly dilute the DM abundance, thereby relaxing the annihilation cross section required to reproduce the observed relic density and opening new regions of viable parameter space. We further analyze the complementarity between current and future direct detection experiments and charged lepton flavour violation (cLFV) searches in probing this scenario. Our results show that next-generation direct detection experiments such as DARWIN and XLZD, together with upcoming cLFV searches (in particular the future sensitivity of $μ\rightarrow 3e$ and $μ\rightarrow e$ conversion experiments), will be capable of testing substantial regions of the parameter space, including those associated with low reheating temperatures.

Figures (6)

• Figure 1: One loop Feynman diagram for neutrino mass generation.
• Figure 2: Left: Inflaton density ($\rho_{\phi}$) and radiation density ($\rho_R$) as functions of the scale factor $a$. Right: Dark matter yield ($m_{N_1}Y_{N_1}$) and equilibrium DM yield ($m_{N_1}Y^{\text{eq}}_{N_1}$) as functions of $x = m_{N_1}/T$. The vertical green line corresponds the reheating temperature, and the horizontal orange line denotes the observed relic density.
• Figure 3: Left: Required values of $\lambda_5$ for different inflaton decay width $\Gamma_{\phi}$ in order to reproduce the observed dark matter relic density. The red line indicates the boundary separating the WIMP and FIMP regimes. Right: Evolution of the dark matter decoupling temperature and the reheating temperature as functions of $\Gamma_{\phi}$.
• Figure 4: Parameter space of the scotogenic model in the $\text{Tr}(Y^{\nu\dagger}Y^{\nu})$–$\lambda_5$ plane (left) and the $\Gamma_{\phi}$–$T$ plane (right), consistent with all theoretical and experimental constraints discussed in Section \ref{['sec:constraints']}. The color scale corresponds to $\Delta_{N_1}$ in the left panel and to $\lambda_5$ in the right panel. Note that all points are consistent with the best-fit neutrino oscillation data and the observed DM relic density within the $2\sigma$ limit.
• Figure 5: Left: Theoretically and experimentally allowed parameter points of the scotogenic model in the $\text{Br}(\mu \to e\gamma)$–$\text{Br}(\mu \to 3e)$ plane. The color scale denotes the inflaton decay width $\Gamma_{\phi}$. Also shown are the current limits from $\mu \to e\gamma$MEG:2016leq (solid red) and $\mu \to 3e$SINDRUM:1987nra (solid green), together with the projected sensitivities from $\mu \to e\gamma$MEGII:2018kmf (dashed red) and $\mu \to 3e$Mu3e:2020gywBlondel:2013ia (dashed green). Right: Scatter plot in the $\text{Br}(\mu \to e\gamma)$–$\text{Br}(\mu \to e;\rm{Ti})$ plane after imposing the current limits from $\text{Br}(\mu \to e;\rm{Ti})$ (solid blue) Wintz:1998rp, together with the projected sensitivity prism, shown as the dashed blue line. Note that all points are consistent with the best-fit neutrino oscillation data and the observed DM relic density within the $2\sigma$ limit.