Revisiting constraints on WIMPs around primordial black holes

Estanis Utrilla Ginés, Olga Mena, and Samuel J. Witte

Phys. Rev. D 106, 063538 – Published 30 September 2022

Abstract

While primordial black holes (PBHs) with masses $M_{PBH} ≳ 10^{- 11} M_{⊙}$ cannot comprise the entirety of dark matter, the existence of even a small population of these objects can have profound astrophysical consequences. A subdominant population of PBHs will efficiently accrete dark matter particles before matter-radiation equality, giving rise to high-density dark matter spikes. We consider here the scenario in which dark matter is comprised primarily of weakly interacting massive particles (WIMPs) with a small subdominant contribution coming from PBHs, and revisit the constraints on the annihilation of WIMPs in these spikes using observations of the isotropic gamma-ray background (IGRB) and the cosmic microwave background (CMB), for a range of WIMP masses, annihilation channels, cross sections, and PBH mass functions. We find that the constraints derived using the IGRB have been significantly overestimated (in some cases by many orders of magnitude), and that limits obtained using observations of the CMB are typically stronger than, or comparable to, those coming from the IGRB. Importantly, we show that $\sim O (M_{⊙})$ PBHs can still contribute significantly to the dark matter density for sufficiently low WIMP masses and p-wave annihilation cross sections.

Received 22 August 2022
Accepted 6 September 2022

DOI:https://doi.org/10.1103/PhysRevD.106.063538

Physics Subject Headings (PhySH)

Cosmic microwave background Dark matter Gamma ray astronomy

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Estanis Utrilla Ginés and Olga Mena

Instituto de Física Corpuscular (IFIC), University of Valencia-CSIC, Parc Científic UV, c/ Catedrático José Beltrán 2, E-46980 Paterna, Spain

Samuel J. Witte

Gravitation Astroparticle Physics Amsterdam (GRAPPA), Institute for Theoretical Physics Amsterdam and Delta Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands and Excellence Cluster ORIGINS, Boltzmannstr. 2, D-85748 Garching, Germany

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 106, Iss. 6 — 15 September 2022

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
The left (right) panel depicts the density profile before (after) WIMP annihilation as a function of radial distance. Results are illustrated for several PBH masses (left), and several redshifts for $M_{PBH} = 10^{4} M_{⊙}$ (right). In the right panel solid and dashed lines denote the effect of s-wave and p-wave WIMP annihilations, respectively.
Reuse & Permissions
Figure 2
95% CL constraints on the fraction of PBHs in the form of dark matter $f_{PBH}$ as a function of PBH mass, assuming a monochromatic and log-normal (with $σ = 2$ ) mass functions (shown in green and blue solid lines, respectively). Results are shown assuming the remaining dark matter is made of a 100 GeV WIMP with s-wave annihilations to $b \bar{b}$ . Results are compared to the limits one would obtain using a maximally conservative treatment of the isotropic gamma-ray background (dashed), see Sec. 3b for a more optimistic analysis. We also illustrate the constraints on the fraction of PBHs in the form of dark matter in the absence of UCMHs from a number of observational probes, see Ref. [76].
Reuse & Permissions
Figure 3
Top panels: The solid (dashed) lines depict the 95% CL constraints on the PBH dark matter fraction as a function of the PBH mass from CMB (conservative $γ$ -ray) observations in hybrid WIMP-PBH models for s- (left panel) and p-wave (right panel) annihilating WIMPs into the $b \bar{b}$ channel. The cross section is assumed to be $⟨ σ_{A} v ⟩ = 3 \times 10^{- 26} / f_{χ} {cm}^{3}$ /s and ${⟨ σ_{A} v ⟩}_{f o} = 3 \times 10^{- 26} / f_{χ} {cm}^{3}$ /s for the s-wave and p-wave annihilating channels, respectively. We illustrate three possible WIMP dark matter masses: 10 GeV, 100 GeV, and 1 TeV. The top left panel also shows the 95% CL limits from the optimistic IGRB model (dotted lines), see main text for details. Bottom left (right) panels: As in the top panels, but for s- (p-) wave annihilating WIMPs into the $e^{-} e^{+}$ channel.
Reuse & Permissions
Figure 4
Same as Fig. 3, but for the case of a 100 MeV particle annihilating through a vector portal coupling. As detailed in Sec. 2a, for this particle mass the dominant annihilation channel is $e^{+} e^{-}$ . The cross section at freeze out is assumed to be $⟨ σ_{A} v ⟩ = 10^{- 28} / f_{χ} {cm}^{3}$ /s for both the s-wave and p-wave cases.
Reuse & Permissions
Figure 5
The left (right) panels depict the annihilation rate per mini-halo and the diffuse injected power density for a PBH fraction $10^{- 6}$ at present ( $z = 0$ ) respectively as a function of the PBH mass for three different DM masses and also for the cases of s-wave (solid lines) and p-wave (dashed lines) annihilations.
Reuse & Permissions
Figure 6
Left panel: Gamma ray spectrum from DM annihilations into the $e^{+} e^{-}$ and $b \bar{b}$ channels for several PBH and dark matter particle masses. For the case $m_{χ} = 100 GeV$ and the $b \bar{b}$ channel, we illustrate separately the contribution from the ICS and prompt gamma ray fluxes (purple and green shaded regions respectively). The data points depict the observations from COMPTEL, EGRET, Fermi-LAT. Right panel: Gamma ray spectrum from DM annihilations within the light dark matter model ( $m_{χ} = 100 MeV$ ) considered here into the $e^{+} e^{-}$ channel. Several PBH masses and fractions are shown for both s-wave and p-wave annihilating channels. The contribution from gamma rays from ICS is negligible in this model, see text for details.
Reuse & Permissions

Physical Review D

covering particles, fields, gravitation, and cosmology