Phys. Rev. D 108, 023014 (2023) - Detecting axionlike particles with primordial black holes

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Detecting axionlike particles with primordial black holes

Kaustubh Agashe, Jae Hyeok Chang, Steven J. Clark, Bhaskar Dutta, Yuhsin Tsai, and Tao Xu

Phys. Rev. D 108, 023014 – Published 14 July 2023

Abstract

Future gamma-ray experiments, such as the e-ASTROGAM and AMEGO telescopes, can detect the Hawking radiation of photons from primordial black holes (PBHs) if they make up a fraction or all of dark matter. PBHs can analogously also Hawking radiate new particles, which is especially interesting if these particles are mostly secluded from the Standard Model sector, since they might therefore be less accessible otherwise. A well-motivated example of this type is axionlike particles (ALPs) with a tiny coupling to photons. We assume that the ALPs produced by PBHs decay into photons well before reaching the Earth, so these will augment the photons directly radiated by the PBHs. Remarkably, we find that the peaks in the energy distributions of ALPs produced from PBHs are different than the corresponding ones for Hawking radiated photons due to the spin-dependent graybody factor. Therefore, we demonstrate that this process will in fact distinctively modify the PBHs’ gamma-ray spectrum relative to the Standard Model prediction. We use monochromatic asteroid-mass PBHs as an example to show that e-ASTROGAM can observe the PBH-produced ALP gamma-ray signal (for masses up to $\sim 60 MeV$ ) and further distinguish it from Hawking radiation without ALPs. By measuring the gamma-ray signals, e-ASTROGAM can thereby probe yet unexplored parameters in the ALP mass and photon coupling.

Received 29 March 2023
Accepted 23 June 2023

DOI:https://doi.org/10.1103/PhysRevD.108.023014

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Classical black holes Gamma ray astronomy

Axion-like particles

Gravitation, Cosmology & AstrophysicsParticles & Fields

Authors & Affiliations

Kaustubh Agashe^1,*, Jae Hyeok Chang ^1,2,†, Steven J. Clark^3,4,5,‡, Bhaskar Dutta^6,§, Yuhsin Tsai^7,∥, and Tao Xu ^8,9,¶

¹Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
²Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
³Department of Physics, Brown University, Providence, Rhode Island 02912-1843, USA
⁴Brown Theoretical Physics Center, Brown University, Providence, Rhode Island 02912-1843, USA
⁵Hood College, Frederick, Maryland 21701, USA
⁶Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77845, USA
⁷Department of Physics, University of Notre Dame, Indiana 46556, USA
⁸Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma 73019, USA
⁹Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel

^*kagashe@umd.edu
^†jaechang@umd.edu
^‡sclark@hood.edu
^§dutta@tamu.edu
^∥ytsai3@nd.edu
^¶tao.xu@ou.edu

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Vol. 108, Iss. 2 — 15 July 2023

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Figure 1
An example of the gamma-ray spectrum from Hawking radiation with the SM case (purple) and the ALP case with $m_{a} = 60 MeV$ (blue), $m_{a} = 30 MeV$ (green), $m_{a} = 10 MeV$ (yellow), and $m_{a} ≪ T_{H}$ (red). The PBH mass is $M_{PBH} = 10^{15} g$ , corresponding to $T_{H} \approx 10 MeV$ , and the energy density fraction of DM is $f_{PBH} = 10^{- 8}$ . In this figure, we assume that the ALP decay length is much shorter than the distance to the sources (PBHs) and consider its decay to be prompt (instantaneous after creation) when calculating the ALP-case flux. The region of interest is chosen to be the Galactic Center with $| R | \leq 5 °$ . Experimental constraints and future sensitivity are shown in black for COMPTEL (solid), Fermi-LAT (solid), and e-ASTROGAM (dashed).
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Figure 2
The ALP parameter space that can be probed by PBHs. The PBH parameters are chosen as $M_{PBH} = 10^{15} g$ , $f_{PBH} = 10^{- 8}$ (red); $M_{PBH} = 10^{16} g$ , $f_{PBH} = 10^{- 5}$ (blue); $M_{PBH} = 10^{17} g$ , $f_{PBH} = 10^{- 2}$ (green). Existing bounds (gray) are taken from [119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134].
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Figure 3
The $3 σ$ contours from the Galactic Center constraining the PBH parameter space, assuming that the underlying “true” model is the ALP case with $m_{a} = 10^{- 1} MeV$ , $M_{PBH} = 10^{16} g$ , and various $f_{PBH, true}$ . The “test” models are (left) the ALP case and (right) the SM case. The “ $⋆$ ” indicates the location of the true model. With increasing $f_{PBH, true}$ , the contours shrink. When the test model matches the true model (as is the case in the left panel), the contours become infinitesimally small, while for a mismatched model (right), they eventually disappear with sufficient data such that no contour may be drawn. We define the values of $f_{PBH, true}$ where the contour disappears in the right panel as “identification of ALP” line in Fig. 4. The values of $f_{PBH, true}$ for contours are shown in each plot.
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Figure 4
PBH differentiability bounds in the $f_{PBH}$ vs $M_{PBH}$ (left) and $f_{PBH}$ vs $m_{a}$ (right) planes. Various curves correspond to the capability to distinguish a PBH signal with the SM case (short dash) and the ALP case (long dash) from the background. Also included are the ALP-case vs. SM-case distinguishability (solid) and past experimental constraints (left: shaded gray and right: dot-dashed). In the $m_{a}$ plane, the shaded region highlights the region that can distinguish an ALP-case signal from an SM-case signal with the far right edge corresponding to the maximum $m_{a}$ allowed.
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Figure 5
The extended black hole mass distribution that mimics the photon spectrum for the ALP case with $m_{a} ≪ T_{H}$ , $M_{PBH} = 10^{15} g$ , and $6 MeV < E_{γ} < 100 MeV$ . The peak near the $M_{PBH} = 10^{15} g$ explains the primary photon peak, while the plateau at large masses is for the peak from ALP decays. To show the goodness of the fit, we show the ratio of the gamma-ray flux between the SM case with the extended mass function and the ALP case in the plot inside. As a result, $f_{PBH}$ for the SM case is more than 200 times larger than $f_{PBH}$ for the ALP case.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Detecting axionlike particles with primordial black holes

Kaustubh Agashe, Jae Hyeok Chang, Steven J. Clark, Bhaskar Dutta, Yuhsin Tsai, and Tao Xu

Phys. Rev. D 108, 023014 – Published 14 July 2023

Abstract

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Physical Review D

covering particles, fields, gravitation, and cosmology

Detecting axionlike particles with primordial black holes

Kaustubh Agashe, Jae Hyeok Chang, Steven J. Clark, Bhaskar Dutta, Yuhsin Tsai, and Tao Xu

Phys. Rev. D 108, 023014 – Published 14 July 2023

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