Intense Gamma-Ray Lines from Hidden Vector Dark Matter Decay

TL;DR

<3-5 sentence high-level summary>The paper studies a dark matter candidate arising from a hidden SU(2) gauge sector whose vector bosons are stabilized by an accidental SO(3) custodial symmetry at the renormalizable level. Custodial symmetry is explicitly broken by dimension-6 operators, causing cosmological DM decay with tree-level two-body final states that yield intense gamma-ray lines, potentially observable by Fermi-LAT when the breaking scale Λ is near the Grand Unification scale. A key, model-agnostic prediction is the presence of monochromatic gamma-ray lines from decays to $\gamma h$ or $\gamma\eta$, along with correlated leptonic and hadronic signatures whose details depend on the operator class; the gamma-line signal stands as a robust indirect detection handle. The authors also refine relic-density calculations by including annihilations with one DM particle in the final state and assess direct-detection prospects, finding the corresponding cross sections can approach current experimental sensitivities across GeV-to-TeV DM masses.

Abstract

Scenarios with hidden, spontaneously broken, non-abelian gauge groups contain a natural dark matter candidate, the hidden vector, whose longevity is due to an accidental custodial symmetry in the renormalizable Lagrangian. Nevertheless, non-renormalizable dimension six operators break the custodial symmetry and induce the decay of the dark matter particle at cosmological times. We discuss in this paper the cosmic ray signatures of this scenario and we show that the decay of hidden vector dark matter particles generically produce an intense gamma ray line which could be observed by the Fermi-LAT experiment, if the scale of custodial symmetry breaking is close to the Grand Unification scale. This gamma line proceeds directly from a tree level dark matter 2-body decay in association with a Higgs boson. Within this model we also perform a determination of the relic density constraints taking into account the dark matter annihilation processes with one dark matter particle in the final state. The corresponding direct detection rates can be easily of order the current experimental sensitivities.

Figures (8)

• Figure 1: Predictions for case A, benchmark 1, with $\tau_\text{DM}=1.7\times10^{28}\,\text{s}$ ($\Lambda = 2.9\times10^{15}\,\text{GeV}$). The upper panels show the positron fraction (left) and the total electron + positron flux (right) compared with experimental data. Dashed lines show the adopted astrophysical background, solid lines are background + dark matter signal (which overlap the background in this plot). The lower left panel shows the gamma-ray signal from dark matter decay, whereas the lower right panel shows the $\bar{p}/p$-ratio: background (dashed line) and overall flux (solid lines, again identical with background).
• Figure 2: Like Fig. \ref{['fig:A5']}, but for case A, benchmark 2, with $\tau_\text{DM}=1.1\times10^{27}\,\text{s}$ ($\Lambda = 3.7\times10^{15}\,\text{GeV}$). The yellow band shows the uncertainty in the anti-proton flux due to the propagation model parameters.
• Figure 3: Like Fig. \ref{['fig:A5']}, but for case C, benchmark 3, with $\tau_\text{DM}=6.0\times10^{26}\,\text{s}$ ($\Lambda = 2.0\times10^{17}\,\text{GeV}$).
• Figure 4: Like Fig. \ref{['fig:A5']}, but for case C, benchmark 4, with $\tau_\text{DM}=1.6\times10^{27}\,\text{s}$ ($\Lambda = 1.2\times10^{16}\,\text{GeV}$).
• Figure 5: Like Fig. \ref{['fig:A5']}, but for case D, benchmark 2, with $\tau_\text{DM}=6.7\times10^{26}\,\text{s}$ ($\Lambda = 1.5\times10^{16}\,\text{GeV}$).