Future Constraints on Primordial Black Holes from MeV Telescopes

Black Holes that are formed promptly in the early universe are one potential component of the universe's dark matter. Such black holes can Hawking radiate, producing radiation with a temperature that is inversely proportional to their mass. For black holes in the mass range of about 10^15 - 10^17 grams, this emission is concentrated in the MeV band, where previous instrumental constraints have been relatively weak. In this paper, we analyze the capability of next-generation MeV telescopes, such as e-ASTROGAM and AMEGO, to observe or constrain such a dark matter signal, utilizing for the first time well-motivated astrophysical background templates extrapolated from Fermi-LAT observations. We show that if primordial black holes are responsible for the previously detected excess of 511 keV gamma-rays, such telescopes could definitively determine the characteristics of the underlying primordial black hole population.

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Constraining Axion-Like Particles with HAWC Observations of TeV Blazars

Very high-energy gamma-rays from distant sources are typically attenuated (absorbed and re-emitted at lower energies) through interactions with the extragalactic background light during their intergalactic propagation. This means that while distant blazars are bright at GeV energies, their emission at TeV energies should be highly suppressed. Interactions with axion-like particles can provide an alterative life for these particles, as TeV photons could convert into axions within blazar magnetic fields, and then propagate effectively through the IGM before reconverting into TeV gamma rays in the Milky Way magnetic field. We search TeV gamma-ray emission from bright blazars using the 3HWC catalog in concert with lower-energy telescopes. We find no evidence for a signal consistent with ALPs, and place constraints on the axion-photon coupling that is consistent with, or slightly stronger than previous limits.

Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey

The extremely strong magnetic fields of neutron stars potentially provide an optimal environment to initiate the conversion of dark matter axions into photon signals. The galactic center remains an exciting target for these searches, because previous studies indicate that it has both a large dark matter and neutron star density. We utilize detailed sureys the galactic center produced by the Breakthrough Listen Project, which are directly targeted at finding evidence of extraterrestrial life in our universe. The high energy resolution of these surveys is optimal for the detection of an axion signal. We find no evidence for a radio line produced by axion-photon conversion, and set strong limits on the axion-photon conversion cross-section, the exact strength of which depends on uncertainties in the underlying neutron star and dark matter population -- uncertainties which can be significantly reduced by upcoming experiments over the next decade.

Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination

The impressive regularity of pulsating neutron stars allow them to be used as extremely acurate "clocks" that operate on Myr or even Gyr timescales. Pulsar timing arrays have taken repeated observations of nearby MSPs over 20 Myr, looking for small deviations which may be due to local gravitational effects affecting either the neutron star environment or local solar neighborhood. We note that these arrays are quickly becoming sensitive to the enhanced dark matter substructure that is expected when the universe goes through a period of Early Matter Domination before the onset of radiation domination during big-bang nucleosynthesis. Current, or near-future, observations (20 years with approximately 70 pulsars), could begin to constrain novel EMDE parameter space -- while future studies including 200 pulsars over 40 years could raise the minimum energy floor for early matter domination as high as 150 MeV.

Cosmic-Ray Positrons Strongly Constrain Leptophilic Dark Matter

Observations of antimatter cosmic-rays are powerful probes of dark matter annihilation -- as they are produced copiously by dark matter annihilation but were thought to only be produced through secondary astrophysical processes. Observations by PAMELA and AMS-02 found a significant excess in cosmic-ray positrons, which attracted significant interest from the dark matter community, but has been more successfully explained through the emission of e+e- pairs by high-energy pulsars. Here, we note that -- in scenarios where pulsars dominate the high-energy positron flux -- the smoothness of the positron spectrum can constrain sub-dominant dark matter contributions. This is particularly true for leptophilic dark matter models that produce significant bumps in the cosmic-ray positron spectrum. Using recently released AMS-02 data, we set strong cosntraints on dark matter annihilation to e+e-, mu+mu- and tau+tau- final states - producing limits which fall below the thermal annihilation cross-section in many models.

First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter

Despite being observed at optical wavelengths since time immemorial, Jupiter has never been directly studied in GeV gamma-rays. This is primarily an instrumental challenge -- but also due to the fact that Jupiter is not expected to be a bright GeV gamma-ray source. However, the proximity of Jupiter, combined with the spectacular sensitivity of the Fermi-LAT, means that Jupiter observations may spark a new frontier in astrophysical studies. Additionally, we show that dark matter models which annihilate through a light mediator may produce a bright Jovian gamma-ray flux, allowing us to test dark matter models inaccessible to any other study. Using 11 years of Fermi-LAT data, and a detailed methodology for removing astrophysical backgorunds, we set strong limits on the Jupiter gamma-ray flux and thus on dark matter annihilation through light mediators, but potentially find exciting evidence for a signal below 15 MeV. The nature of this signal will require upcoming MeV instruments, like AMEGO or e-ASTROGAM to verify.

Celestial-Body Focused Dark Matter Annihilation

Dark Matter searches traditionally proceed through either direct methods (searching for dark matter scattering with standard model particles), or through indirect methods (through dark matter annihilation into standard model particles). We propose a new search that proceeds through a combination of scattering and annihilation. Dark Matter particles in the galaxy scatter with celestial bodies (most importantly brown dwarfs and neutron stars). They become trapped inside and their density increases until they annihilate. If this annihilation proceeds through a light-mediator capable of escaping the compact object, its subsequent decay into standard model particles can produce a detectable signature similar to standard annihilation. However, the morphology and amplitude of the signal have detectable differences because the annihilation rate depends on the rate of dark matter capture. We show that current gamma-ray constraints can place strong limits on the dark matter scattering cross-section in these models, outperforming both standard direct detection experiments and previous Solar gamma-ray searches.

Full Publication List:

51. The Sensitivity of Future Gamma-Ray Telescopes to Primordial Black Holes
Celeste Keith, Dan Hooper, Tim Linden, Rayne Liu
To Be Submitted

50. Constraining Axion-Like Particles with HAWC Observations of TeV Blazars
Sunniva Jacobsen, Tim Linden, Katherine Freese
To Be Submitted

49. Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey
Joshua Foster, Samuel Witte, Matthew Lawson, Tim Linden, Vishal Gajjar, Christoph Weniger, Ben Safdi
Submitted to PRL

48. Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination
Sten Delos, Tim Linden
Accepted by PRD

47. Cosmic-Ray Positrons Strongly Constrain Leptophilic Dark Matter
Isabelle John, Tim Linden
Journal of Cosmology and Astroparticle Physics 12 2021 007

46. Response to Comment on: "Dark Matter Annihilation Can Produce a Detectable Antihelium Flux through Λb Decays
Martin Winkler, Tim Linden
ArXiv Only

45. First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter
Rebecca Leane, Tim Linden
Submitted to PRL

44. Celestial-Body Focused Dark Matter Annihilation Throughout the Galaxy
Rebecca Leane, Tim Linden, Payel Mukhopadhyay, Natalia Toro
Physical Review D, 103 (2021) 7

43. Dark Matter Annihilation Can Produce a Detectable Antihelium Flux through Λb Decays
Martin Wolfgang Winkler, Tim Linden
Physical Review Letters 126 101101

42. Anti-Deuterons and Anti-Helium Nuclei from Annihilating Dark Matter
Ilias Cholis, Tim Linden, Dan Hooper
Physical Review D 102 103019

41. Breaking a Dark Degeneracy: The gamma-ray signature of early matter domination
M. Sten Delos, Tim Linden, Adrienne Erickcek
Physical Review D 100 123546

40. A Robust Method for Treating Astrophysical Mismodeling in Dark Matter Annihilation Searches of Dwarf Spheroidal Galaxies
Tim Linden
Physical Review D 043017

39. A Robust Excess in the Cosmic-Ray Antiproton Spectrum: Implications for Annihilating Dark Matter
Ilias Cholis, Tim Linden, Dan Hooper
Physical Review D 99 103026

38. Constraints on Spin-Dependent Dark Matter Scattering with Long-Lived Mediators from TeV Observations of the Sun with HAWC
HAWC Collaboration
Physical Review D 98 123012

37. Millisecond Pulsars, TeV Halos, and Implications for the Galactic Center Gamma-Ray Excess
Dan Hooper, Tim Linden
Physical Review D 98 043005

36. Comment on "Characterizing the Population of Pulsars in the Galactic Bulge with the Fermi Large Area Telescope" [arXiv: 1705.00009v1]
Richard Bartels, Dan Hooper, Tim Linden, Siddharth Mishra-Sharma, Nick Rodd, Ben Safdi, Tracy Slatyer
Physics of the Dark Universe 20 88 2018

35. Searching for Dark Matter with Neutron Star Mergers and Quiet Kilonovae
Joe Bramante, Tim Linden, Yu-Dai Tsai
Physical Review D 97 055016

34. Dark Kinetic Heating of Neutron Stars: An Infrared Window On WIMPs, SIMPs, and Higgsinos
Masha Baryakhtar, Joe Bramante, Shirley Li, Tim Linden, Nirmal Raj
Physical Review Letters 119 131801

33. Low Mass X-Ray Binaries in the Inner Galaxy: Implications for MSPs and the GeV Excess
Daryl Haggard, Craig Heinke, Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1705 05 056

32. The Angular Power Spectrum of diffuse gamma-rays measured by Fermi and DM constraints
M. Fornasa, A. Cuoco, J. Zavala, J. Gaskins, M. Sanchez-Conde, G. Gomez-Vargas, E. Komatsu, Tim Linden, F. Prada, F. Zandenel, A. Morselli
Physical Review D 94, 123005

31. The Gamma-Ray Pulsar Population of Globular Clusters: Implications for the GeV Excess
Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1608 08 018

30. Indirect Detection Constraints on s and t Channel Simplified Models of Dark Matter
Linda Carpenter, Russell Colburn, Jessica Goodman, Tim Linden
Physical Review D 94 055027

29. Radio Galaxies Dominate the High-Energy Diffuse Gamma-Ray Background
Dan Hooper, Tim Linden, Alejandro Lopez
Journal of Cosmology and Astroparticle Physics 1608 08 019

28. The High-Energy Tail of the Galactic Center Gamma-Ray Excess
Tim Linden, Nicholas Rodd, Benjamin Safdi, Tracy Slatyer
Physical Review D 94, 103013

27. Improved Cosmic-Ray Injection Models and the Galactic Center Gamma-Ray Excess
Eric Carlson, Tim Linden, Stefano Profumo
Physical Review D 94 063504

26. Is the Gamma-Ray Source J2212.5+0703 A Dark Matter Subhalo?
Bridget Bertoni, Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1609 05 049

25. On the R-Process Enrichment of Dwarf Spheroidal Galaxies
Joseph Bramante, Tim Linden
The Astrophysical Journal 826 1 57

24. Putting Things Back Where They Belong: Tracing Cosmic-Ray Injection with H2
Eric Carlson, Tim Linden, Stefano Profumo
Physical Review Letters 117 111101

23. Known Radio Pulsars Do Not Contribute to the Galactic Center Gamma-Ray Excess
Tim Linden
Physical Review D 93 6 063003

22. The Galactic Center GeV Excess from a Series of Leptonic Cosmic-Ray Outbursts
Ilias Cholis, Carmelo Evoli, Francesca Calore, Tim Linden, Christoph Weniger, Dan Hooper
Journal of Cosmology and Astroparticle Physics 1512 12 005

21. Examining the Fermi-LAT Third Source Catalog in Search of Dark Matter Subhalos
Bridget Bertoni, Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1512 12 035

20. On the Gamma-Ray Emission from Reticulum II and Other Dwarf Galaxies
Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics 1509 09 016

19. The Galactic Center Excess in Gamma-Rays from Annihilation of Self-Interacting Dark Matter
Manoj Kaplinghat, Tim Linden, Haibo Yu
Physical Review Letters, 114 211303

18. The Anisotropy of the Extragalactic Radio Background from Dark Matter
Ke Fang, Tim Linden
Physical Review D 91 083501 (2015)

17. What Does the PAMELA Antiproton Spectrum Tell Us About Dark Matter?
Dan Hooper, Tim Linden, Philipp Mertsch
Journal of Cosmology and Astroparticle Physics 03 021 (2015)

16. Improving the Sensitivity to Dark Matter Annihilation in Dwarf Spheroidal Galaxies
Eric Carlson, Dan Hooper, Tim Linden
Physical Review D, 91 061302 (2015)

15. A Critical Reevaluation of Radio Constraints on Annihilating Dark Matter
Ilias Cholis, Dan Hooper, Tim Linden
Physical Review D, 91 083507 (2015)

14. Challenges in Explaining the Galactic Center Gamma-Ray Excess with Millisecond Pulsars
Ilias Cholis, Dan Hooper, Tim Linden
Journal of Cosmology and Astroparticle Physics, 06 043 (2015)

13. Detecting Dark Matter with Imploding Pulsars in the Galactic Center
Joseph Bramante, Tim Linden
Physical Review Letters, 113 191301

12. Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud
Alex Drlica-Wagner, German Gomez-Vargas, Jack Hewitt, Tim Linden, Luigi Tibaldo
The Astrophysical Journal, 790 24

11. The Characterization of the Gamma-Ray Signal from the Central Milky Way
Tansu Daylan, Doug Finkbeiner, Dan Hooper, Tim Linden, Stephen Portillo, Nicholas Rodd, Tracy Slatyer
Physics of the Dark Universe 12 2016 1

10. Antihelium from Dark Matter
Eric Carlson, Adam Coogan, Tim Linden, Stefano Profumo, Alejandro Ibarra, Sebastian Wild
Physical Review D, 89 076005

9. Tying Dark Matter to Baryons with Self-Interactions
Manoj Kaplinghat, Ryan Keeley, Tim Linden, Haibo Yu
Physical Review Letters, 113 021302 (2014)

8. Pulsars Cannot Account for the Inner Galaxy's GeV Excess
Dan Hooper, Ilias Cholis, Tim Linden, Jennifer Siegal-Gaskins, Tracy Slatyer
Physical Review D, 88 083009

7. A Clustering Analysis of the 130 GeV Gamma-Ray Feature
Eric Carlson, Tim Linden, Stefano Profumo, Christoph Weniger
Physical Review D, 88 043006

6. Are Lines from Unassociated Gamma-Ray Sources Evidence for Dark Matter Annihilation?
Dan Hooper, Tim Linden
Physical Review D, 86 8 083532

5. Gamma-Rays in the Fermi-LAT Data: Is it a Bubble?
Stefano Profumo, Tim Linden
Journal of Cosmology and Astroparticle Physics, 007 011

4. The Isotropic Radio Background and Annihilating Dark Matter
Dan Hooper, Alexander Belikov, Tesla Jeltema, Tim Linden, Stefano Profumo, Tracy Slatyer
Physical Review D, 86 10 103003

3. Origin of Gamma-Rays from the Galactic Center
Dan Hooper, Tim Linden
Physical Review D, 84 12 123005

2. Dark Matter and Synchrotron Emission from Galactic Center Radio Filaments
Tim Linden, Dan Hooper, Farhad Yusef-Zadeh
The Astrophysical Journal, 741 2 95

1. Gamma-Rays from the Galactic Center and the WMAP Haze
Dan Hooper, Tim Linden
Physics Review D, 83 8 083517 (2011)



Tim Linden

Assistant Professor, Stockholm University

linden@fysik.su.se