Constraints to the inert doublet model of dark matter with very high-energy gamma-rays observatories

Abstract

We investigate the constraints on the Inert Doublet Model (IDM), a minimal extension of the Standard Model of Particle Physics featuring a scalar dark matter candidate, using data from recent and future gamma-ray observatories. The relevance of the model for indirect searches of dark matter stems from two key features: first, in the high-mass regime, IDM can achieve the correct dark matter relic abundance for masses between approximately 500 GeV and 25 TeV, aligning perfectly with the energy sensitivity of Imaging Atmospheric Cherenkov Telescopes. Second, this regime is dominated by co-annihilation processes, which elevate the thermal-relic velocity-weighted annihilation cross-section to the range of 0.5 $-$ 1.0$\times 10^{-25}$ cm$^3$ s$^{-1}$, thereby enhancing the potential gamma-ray signal from dark matter annihilation. Analyzing recent H.E.S.S. observations of the Galactic Center region, we find that dark matter particle masses within the 1 to 8 TeV range are excluded by current data. Furthermore, we project that the Cherenkov Telescope Array Observatory (CTAO) will comprehensively probe the remaining viable parameter space of the IDM. Our findings are further examined in the context of the most recent theoretical constraints, collider searches, and direct detection results from the LUX-ZEPLIN experiment.

Figures (5)

• Figure 1: Random scan in the $\lambda_{345} \times m_H$ parameter space of the IDM. Each point represents a scenario that agrees with unitarity (cut-1) and relic abundance $\Omega \, h^2 = 0.1200$ (cut-2). Direct detection (DD) exclusion from LZ (cut-3) is represented in green. Yellow points: satisfy relic abundance but are excluded by direct detection. Red points: satisfy relic abundance and direct detection.
• Figure 2: Color map of the relic abundance $\Omega \, h^2$ at logarithmic scale in the $\lambda_{345} \times m_H$ parameter space for the discrete scan. Each row corresponds to one of the mass splittings $\Delta_+ = \left( 0.5, 1, 5, 10 \right) \text{GeV}$ and each column to one $\Delta_o$ in the same selection of values. Black lines: correct relic abundance. Green lines: LZ exclusion limits. Orange band: unitarity constraint. Grey band: inertness constraint. See the text for details.
• Figure 3: Compilation of constraints to the IDM in the annihilation thermal-averaged velocity-weighted cross-section versus DM particle mass ($\left< \sigma \, v \right> \times m_{DM}$) space: relic abundance (red lines), direct detection exclusion limits at 90% C.L. from LZ (green lines) and indirect detection expected limits at 95% C.L. for H.E.S.S. (purple lines) and for CTAO (blue lines), both at the Galactic Center. Each row corresponds to one of the mass splittings $\Delta_+ = \left( 0.5, 1, 5, 10 \right) \text{GeV}$ and each column to one $\Delta_o$ in the same selection of values. The unitarity upper bound for mass is shown in orange. The viable models are the ones on the red curves, which are below the direct and indirect detection limits.
• Figure 4: Sensitivity of gamma-ray observatories to the Inert Doublet Model. Points in red represent viable scenarios obtained in the random scan that satisfy unitarity, relic abundance, and direct detection limits. Green dots are the benchmark points, including the Sommerfeld enhancement computed in Garcia-Cely:2015khw, and the CTA and H.E.S.S. limits used in their work are shown in continuous and dashed lines.
• Figure 5: Distribution of branching ratios $B_i$ for the main channels of DM annihilation in the IDM: $W^+ W^-$, $Z Z$, $h h$, and $\gamma W^+ W^-$. Each column represents one of these channels, and each row is the sample of scenarios considered.