Dark Matter Searches

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  1. Tim Linden, Jung-Tsung Li, Bei Zhou, Isabelle John, Milena Crnogorčević, Annika Peter, John Beacom
  2. 2505.04625

Gamma Rays in a Halo Around the Sun

The Sun is one of the brightest gamma-ray sources in the sky. The gamma-ray emission comes from two processes: First, high-energy cosmic-ray protons hit the solar surface and produce outgoing gamma-rays via hadronic interactions. Second, high-energy electrons and positrons upscatter starlight to gamma-ray energies via inverse-Compton scattering. This forms a bright, diffuse halo of gamma-ray emission around the Sun. We use 15 years of Fermi-LAT data to observe the spectrum, morphology, time-variation, and azimuthal distribution of gamma-rays from the solar halo, detecting bright emission between 31.6 MeV and 100 GeV, and out to 45 degress from the Sun. The morphology and spectrum of the emission is primarily governed by solar modulation, and we set strong constraints on the solar modulation potential in regions near the Sun that are inaccessible to local cosmic-ray probes of solar dynamics.

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Research Topics
  1. Thong Nguyen, Tim Linden, Pierluca Carenza, Axel Widmark
  2. 2501.14864
SuperK Observations Strongly Constrain Leptophilic Dark Matter Scattering

Leptophilic dark matter models (which primarily couple to leptonic standard model particles), are a well-motivated class of dark matter models that can explain several anomalies in the neutrino and charged-lepton sectors (for example, g-2). However, these models are difficult to target with traditional direct detection, because they do not benefit from the A^4 enhancement typical of spin-independent nuclear scattering. The huge electron density in the Sun makes it a compelling target for these searches -- and fortunately, our efforts to search for dark matter capture in the Sun are highly enhanced in leptonic models, because any subsequent dark matter annihilation will produce a high-energy neutrino flux that escapes the Sun and is detectable from Earth. We use 10 years of SuperK observations, which have not detected any neutrino excess from the Sun above 100 MeV, to strongly constrain this class of models -- obtaining constraints that exceed terrestrial direct detection by an order of magnitude across many leptophilic annihilation states. These results (along with the promise of upcoming HyperK data) indicate that solar neutrino searches may provide the strongest constraints on leptophilic dark matter scattering.

  1. Milena Crnogorčević, Sten Delos, Nadia Kuritzén, Tim Linden
  2. 2501.14865
Galaxy Clusters Provide World-Leading Constraints on Dark Matter in Prompt Cusps

Recent studies have found that dark matter can form prompt cusps in the very early universe, and that --- contrary to previous estimates --- these cusps can survive until the present day so long as they are not in regions with particularly large baryonic densities. The annihilation inside these cusps dominates the total annihilation rate despite their small size -- and makes the largest dark matter structures (which have the most cusps) the most important targets for dark matter indirect detection. We use 15 years of data to investigate dark matter signals from the prompt cusps in galaxy clusters. We find no excess and place strong limits on the dark matter annihilation cross-section, ruling out dark matter annihilating at the thermal cross-section below 200 GeV, and placing our result in tension with dark matter models aimed to explain the galactic center excess.

  1. Aurelio Amerio, Dan Hooper, Tim Linden
  2. 2412.05220
Improved Measurements of the MSP Luminosity Function in Globular Clusters

The nature of the Galactic Center excess has been debated for over a decade -- with dark matter and millisecond pulsars as the two leading candidates. We use measurements of globular clustetrs, which have bright GeV gamma-ray fluxes which are thought to be powered by populations of MSPs, in order to calculate the luminosity function of MSPs. We produce a world-leading calculation for the luminosity function of these sources. If a similar luminosity function existed for detectable MSPs in the galactic center, we would expect more observed sources than have presently been found. Unless there is either a large missing cache of unassociated Fermi sources that are MSPs, or the MSP luminosity function is catagorically dimmer than in globular clusters -- this strongly limits the potential for MSPs to contribute to the Galactic center excess.

  1. Thong Nugyen, Isabelle John, Tim Linden, Tim Tait
  2. 2412.00180
X-ray and Positron constraints on dark photon and scalar dark matter

We set world leading constraints on the decay of dark photon and scalar dark matter models. This work goes beyond previous studies, which investigate single final state decay products (such as electrons, or bottom-quarks) in order to self-consistently explore the full decay width calculation for well-motivated dark matter/standard model couplings. We rule out dark matter decays on timescales that reach up to 1e25 seconds at the MeV scale, and up to 1e29 seconds by using AMS-02 data at the GeV scale. We discuss the application of these results to more generic dark matter model building.

  1. Pedro De la Torre Luque, Tim Linden
  2. 2408.05179
Galactic Gas Models Systematically Affect Diffusive Halo Height Models

Observations of radioactive secondary ratios (e.g., 10Be/9Be) which are produced when two secondary isotopes are formed in known abundance ratios, provide excellent cosmic clocks, due to the fact that the abundance ratio predictably changes as a function of time. This is potentially of great interest, because it allows for detailed measurements of cosmic-ray diffusion throughout the Milky Way halo. We point out a critical, but previous unappreciated systematic, the very local distribution of galactic gas, which signifcantly inhibits our ability to use isotopic ratios to study galactic diffusion. Because the best isotopic ratio measurements are produced at low energies (where magnetic fields can best descrminate between particles of different masses), the radioactive component necessarily propagates only a short distance in the galaxy, and our observations are highly biased towards very local gas structures. We show that utilizing detailed spiral arms models can change our best-fit constraints on the galactic halo height by a factor of 4, indicating that more detailed understanding of local gas is necessary in order to take advantage of upcoming isotopic measurements.

  1. Tim Linden, Thong Nguyen, Tim Tait
  2. 2406.19445
X-Ray Constraints on Dark Photon Tridents

We investigate models where keV dark photons compose the dark matter. Such photons can kinetically couple and decay into standard model particles. At masses below twice the electron mass, most standard model final states are kinematically inaccessible, making the dominant decay path the decay into a three-photon trident. This produces a unique spectral signature in x-ray observations. We utilize 16 years of INTEGRAL data to set world leading constraints on the dark photon kinetic coupling at energies between 90 keV up to 1 MeV. Our results exceed current direct detection bounds by orders of magnitude, especially at energies above 200 keV, and improve previous x-ray constraints by up to a factor of 100.

Full Publication List:

76. First Observations of Solar Halo Gamma Rays Over a Full Solar Cycle
 Tim Linden, Jung-Tsung Li, Bei Zhou, Isabelle John, Milena Crnogorčević, Annika Peter, John Beacom
To Be Submitted

75. Super-Kamiokande Strongly Constrains Leptophilic Dark Matter Capture in the Sun
 Thong Nguyen, Tim Linden, Pierluca Carenza, Axel Widmark
To Be Submitted

74. Gamma-Ray Observations of Galaxy Clusters Strongly Constrain Dark Matter Annihilation in Prompt Cusps
 Milena Crnogorčević, Sten Delos, Nadia Kuritzén, Tim Linden
To Be Submitted

73. Millisecond Pulsars in Globular Clusters and Implications for the Galactic Center Gamma-Ray Excess
 Aurelio Amerio, Dan Hooper, Tim Linden
To Be Submitted

72. Strong Constraints on Dark Photon and Scalar Dark Matter Decay from INTEGRAL and AMS-02
 Thong Nugyen, Isabelle John, Tim Linden, Tim Tait
To Be Submitted

71. Galactic Gas Models Strongly Affect the Determination of the Diffusive Halo Height
 Pedro De la Torre Luque, Tim Linden
Journal of Cosmology and Astroparticle Physics 02 062 (2025)

70. X-Ray Constraints on Dark Photon Tridents
 Tim Linden, Thong Nguyen, Tim Tait
To Be Submitted

69. Dark Branches of Immortal Stars at the Galactic Center
 Isabelle John, Rebecca Leane, Tim Linden
To Be Submitted

68. Cosmic-Ray Propagation Models Elucidate the Prospects for Antinuclei Detection
 Pedro De la Torre Luque, Martin Winkler, Tim Linden
Journal of Cosmology and Astroparticle Physics 10 017 (2024)

67. Indirect Searches for Dark Photon-Photon Tridents in Celestial Objects
 Tim Linden, Thong Nguyen, Tim Tait
To Be Submitted

66. Antiproton Bounds on Dark Matter Annihilation from a Combined Analysis Using the DRAGON2 Code
 Pedro De la Torre Luque, Martin Winkler, Tim Linden
Journal of Cosmology and Astroparticle Physics 10.1088 104 2024

65. Dark Matter Scattering Constraints from Observations of Stars Surrounding Sgr A*
 Isabelle John, Rebecca Leane, Tim Linden
Physical Review D 109 12 123041 (2024)

64. Strong Constraints on Dark Matter Annihilation in Ursa Major III/UNIONS 1
 Milena Crnogorčević, Tim Linden
Physical Review D 109 8 083018 (2024)

63. Gamma-ray lines in 15 years of Fermi-LAT data: New constraints on Higgs portal dark matter
 Pedro De la Torre Luque, Tim Linden, Juri Smirnov
Physical Review D 109 (2024) 4, L041301

62. Limits on dark matter annihilation in prompt cusps from the isotropic gamma-ray background
 M. Sten Delos, Michael Korsmeier, Axel Widmark, Carlos Blanco, Tim Linden, Simon White
Physical Review D 109 8 083512 (2024)

61. Accurate Inverse-Compton Models Strongly Enhance Leptophilic Dark Matter Signals
 Isabelle John, Tim Linden
Physical Review D 108 10 103022

60. On the gamma-ray emission from the core of the Sagittarius dwarf galaxy
 Addy Evans, Louis Strigari, Oskar Svenborn, Andrea Albert, Pat Harding, Dan Hooper, Tim Linden, Andrew Pace
Monthly Notices of the Royal Astronomical Society 524 3 4574

59. The Cherenkov Telescope Array Will Test Whether Pulsars Generate the Galactic Center Gamma-Ray Excess
 Celeste Keith, Dan Hooper, Tim Linden
Physical Review D 107 10, 103001

58. The TeV Sun Rises: Discovery of Gamma rays from the Quiescent Sun with HAWC
 HAWC Collaboration
Physical Review Letters 131, 051201 (2023)

57. Cosmic Ray Antihelium from a Strongly Coupled Dark Sector
 Martin Winkler, Pedro De la Torre Luque, Tim Linden
Physical Review D 107 12 123035 (2023)

56. White Dwarfs in Dwarf Spheroidal Galaxies: A New Class of Compact-Dark-Matter Detectors
 Juri Smirnov, Ariel Goobar, Tim Linden, Edvard Mörtsell
Physical Review Letters 132 15 151401 (2024)

55. The Sensitivity of Future Gamma-Ray Telescopes to Primordial Black Holes
 Celeste Keith, Dan Hooper, Tim Linden, Rayne Liu
Physical Review D 106 (2022) 4, 043003

54. Constraining Axion-Like Particles with HAWC Observations of TeV Blazars
 Sunniva Jacobsen, Tim Linden, Katherine Freese
Journal of Cosmology and Astroparticle Physics 10 009

53. Extraterrestrial Axion Search with the Breakthrough Listen Galactic Center Survey
 Joshua Foster, Samuel Witte, Matthew Lawson, Tim Linden, Vishal Gajjar, Christoph Weniger, Ben Safdi
Physial Review Letters 129, 251102 (2022)

52. Dark Matter Microhalos in the Solar Neighborhood: Pulsar Timing Signatures of Early Matter Domination
 Sten Delos, Tim Linden
Physical Review D 105 123514

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

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

49. First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter
 Rebecca Leane, Tim Linden
Physical Review Letters 131 7 071001

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

47. First Observations of Solar Disk Gamma Rays over a Full Solar Cycle
 Tim Linden, John Beacom, Annika Peter, Benjamin Buckman, Bei Zhao, Guanying Zhu
Physical Review D 105 (2022) 6, 063013

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

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

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

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

42. 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

41. 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

40. First HAWC Observations of the Sun Constrain Steady TeV Gamma-Ray Emission
 HAWC Collaboration
Physical Review D 98 123011

39. An Unexpected Dip in the Solar Gamma-Ray Spectrum
 Qing-Wen Tang, Kenny Ng, Tim Linden, Bei Zhou, John Beacom, Annika Peter
Physical Review D, 98 063019

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

37. Evidence for a New Component of High-Energy Solar Gamma-Ray Production
 Tim Linden, Bei Zhou, John Beacom, Annika Peter, Kenny Ng, Qing-Wen Tang
Physical Review Letters 121 131103

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)

Theses
Dark Matter Annihilation at the Galactic Center

Doctoral Thesis
13 June 2013

White Papers
Snowmass2021 Cosmic Frontier White Paper: Puzzling Excesses in Dark Matter Searches and How to Resolve Them

Rebecca Leane et al.
14 March 2022

All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe

AMEGO Collaboration
17 July 2019

Looking Under a Better Lamppost: MeV-scale Dark Matter Candidates

Regina Caputo et al.
14 March 2019

Positron Annihilation in the Galaxy

Carolyn Kierens et al.
13 March 2019

Tim Linden

Assistant Professor, Stockholm University

linden@fysik.su.se