Scalar Multiplet Dark Matter

TL;DR

This work investigates scalar dark matter candidates as neutral components of SU(2)_L multiplets up to 7-plets, emphasizing the impact of scalar quartic couplings beyond the pure gauge limit. Using relic-density calculations in the high-mass regime, it shows that scalar interactions can significantly enhance (co)annihilation rates, broadening the viable DM mass range from the purely gauge case and modifying direct and indirect detection predictions. The analysis provides detailed predictions for the Inert Doublet Model and higher multiplets, including Sommerfeld effects for very heavy DM and the dependence on λ3, while ensuring consistency with vacuum stability and perturbativity up to high scales. Additionally, the paper outlines how adding right-handed neutrinos to the doublet model can realize neutrino masses and TeV-scale leptogenesis in a minimal way, linking DM, the neutrino sector, and baryogenesis in a testable framework. Overall, the results show that scalar multiplet DM remains a compelling and highly predictive scenario with rich collider, direct-detection, and indirect-detection phenomenology.

Abstract

We perform a systematic study of the phenomenology associated to models where the dark matter consists in the neutral component of a scalar SU(2)_L n-uplet, up to n=7. If one includes only the pure gauge induced annihilation cross-sections it is known that such particles provide good dark matter candidates, leading to the observed dark matter relic abundance for a particular value of their mass around the TeV scale. We show that these values actually become ranges of values -which we determine- if one takes into account the annihilations induced by the various scalar couplings appearing in these models. This leads to predictions for both direct and indirect detection signatures as a function of the dark matter mass within these ranges. Both can be largely enhanced by the quartic coupling contributions. We also explain how, if one adds right-handed neutrinos to the scalar doublet case, the results of this analysis allow to have altogether a viable dark matter candidate, successful generation of neutrino masses, and leptogenesis in a particularly minimal way with all new physics at the TeV scale.

Figures (15)

• Figure 1: Dark matter relic abundance in the pure gauge limit as a function of the DM mass. Dashed (Solid) curve : Instantaneous freeze-out approximation without (with) velocity-dependent terms in $\sigma v$. Points : Output from MicrOMEGAs
• Figure 2: Maximal scalar quartic couplings (left panel) and mass splittings (right panel) as a function of mass, imposed by the WMAP bound. Notice that $|\lambda_{H_0}|$ is maximal for negative values of $\lambda_{H_0}$. Asymptotic values of the maximum splittings are given in Eq. (\ref{['maxsplitval']}).
• Figure 3: Contours of $\lambda$ for the WMAP value $\Omega_{\rm DM} h^2 = 0.1131 \pm 0.0034$ for $m_{H_0}=600$ (interior), $1000,\;3000$ (exterior) GeV, with $m_{A_0}=m_{H_0}$ (left panel) and $m_{H_c}=(m_{H_0}+m_{A_0})/2$ (right panel). Dashed curve corresponds to the approximate ellipsoid.
• Figure 4: Maximal values of scalar quartic couplings (left panel) and mass splittings (right panel) as a function of the DM mass, constrained by WMAP, without (dashed lines) and with (thin solid lines) the vacuum stability conditions Eq. (\ref{['vacstab']}) included. We assume a Higgs mass $m_h=120$ GeV, and a sharp threshold between the freeze-out in the broken and in the unbroken phases of the SM at a mass $m_{H_0}=5$ TeV.
• Figure 5: Evolution of the mass of the dark matter candidate as a function of the coupling $\lambda_3$ for all the higher multiplet models of phenomenological interest, as constrained by WMAP, without (solid lines) or with (dashed lines) Sommerfeld effect. The curves correspond, from top to bottom at $\lambda_3 = 0$, to the real septuplet, the real quintuplet and the real triplet. The shaded area on the left is excluded by the vacuum stability constraint (for $m_h=120$ GeV and $\lambda_2^{max}=4\pi$).