Testable dark matter solution within the seesaw mechanism

Abstract

The presence of a dark matter component in the Universe, together with the discovery of neutrino masses from the observation of the oscillation phenomenon, represents one of the most important open questions in particle physics today. A concurrent solution arises when one of the right-handed neutrinos, necessary for the generation of light neutrino masses, is itself the dark matter candidate. In this article, we study the generation of such a dark matter candidate relying solely on the presence of neutrino mixing. This tightly links the generation of dark matter with searches in laboratory experiments on top of the usual indirect dark matter probes. We find that the regions of parameter space producing the observed dark matter abundance can be probed indirectly with electroweak precision observables and charged lepton flavor violation searches. Given that the heavy neutrino masses need to lie at most around the TeV scale, probes at future colliders would further test this production mechanism.

Figures (5)

• Figure 1: DM production rate (blue line) as a function of $\tau$ for $y=3$. The black line is the Hubble expansion rate, showing $\Gamma_{\mathrm{DM}}\ll H$, while the red one corresponds to the heavy pseudo-Dirac neutrino yield, $Y_N$. The dark gray area highlights the symmetric Higgs phase, while the light gray region corresponds to $\tau<\tau_{\mathrm{in}}$ (see Eq. (\ref{['eq:DM_fraction']})).
• Figure 2: Results for regions of parameter space producing at least $1$ % of the observed DM for NO. The upper panel shows the results on the DM mixing vs DM mass plane, with the color bar representing the DM fraction. The lower panel shows the DM fraction as a function of the active-heavy mixing. The DM mixing is shown in the corresponding color bar. Relevant experimental and observational bounds are shown in each slice of parameter space (see text for details).
• Figure 3: Prospects to probe the parameter space generating $10^{-1}\lesssim \mathcal{F}_{\mathrm{DM}}\lesssim 5$. In the upper panel we show correlations between the invisible decay width of the $Z$-boson and searches for $\mu\rightarrow e\gamma$, together with prospective sensitivities for FCC-ee and MEG-II. In the lower panel we present the relevant parameter space for the active-heavy mixing $|U_{\mu N}|^2$ and $m_N$ including relevant experimental bounds Fernandez-Martinez:2023phjBlennow:2023mqx. The purple line corresponds to the sensitivity of FCC-hh Abdullahi:2022jlv.
• Figure 4: Feynman diagrams contributing to the neutrino self-energy. In the SM extension with singlet fermions, there is the Higgs contribution (left) and the gauge contribution from the $W$ and $Z$ bosons (right). The imaginary part of the self-energy is related to the rate at which each species approaches equilibrium.
• Figure 5: Temperature evolution of the Higgs vev given by Eq. (\ref{['eq:Higgs_vev']}) (left panel) and the temperature dependent Higgs mass including the leading thermal corrections (right panel). Additionally, we show the evolution of the gauge boson masses which are proportional to the Higgs vev. The gray shaded area corresponds to temperatures $T\gtrsim 130$ GeV for which we do not compute the DM production.