Publications

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.

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.

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.

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.

The Dark Main Sequence

Dark Matter can accumulate and annihilate within stars, depositing energy in the stellar core which travels outward and provides pressure support and eventually thermal radiation. This process is qualitatively identical to fusion, and in regions with very high dark matter densities (such as the galactic center) the dark matter induced power can exceed nuclear fusion to produce a dark matter powered star. We show that stars powered by dark matter are situated along a dark Hertzsprung-Russel diagram, with properties similar to, but observationally separable from the the standard Hertzsprung-Russel Diagram of fusion powered stars. Two important observables are: (1) an extremely top-heavy initial mass function, as the lowest mass stars are predominantly disrupted while heavier main sequence stars become effectively immortal due to the limitless dark matter fuel, (2) two new dark branches of stars situated along the Henyey and Hayashi tracks, which would not be normally observable in standard stellar evolution.

Prospects for Antinuclei Detection in Light of Antiproton Limits

AMS-02 has tentatively observed a handful of heavy antinuclei events most consistent with a flux of antihelium nuclei that exceeds the expected flux from cosmic-ray propagation models. We pproduce updated models of cosmic-ray propagation that correctly take into account recently updated nuclear cross-section measurements and observational constraints from recently released AMS-02 data. We find that standard astrophysical production models should produce no more than ~0.1 antihelium events, and approximately 1 antideutron event. Dark Matter annihilation can produce a larger antinuclei flux, with an expectation of approximately 1 event for standard annihilation models, but potentially many more events if optimistic models of Lambda-b driven antihelium production are accurate. If any antihelium-4 is discovered, novel physics is required.

Using Celestial Bodies to Search for Dark Photon-Photon Tridents

We analyze a novel signal, the annihilation of dark matter through a low-mass dark photon mediator into a trident of three gamma-rays. This produces a hard spectral signal which is unique compared to other gamma-ray indirect detection targets. Moreover, the dark photon may be long lived, allowing it to escape from celestial bodies. We peform a detailed analysis of the dark photon-photon trident signal and then analyze gamma-ray data on both solar system and galactic center targets, placing strong limits on the dark matter/baryon coupling in such scenarios.

Full Publication List:

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

67. 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

66. Galactic Gas Models Strongly Affect the Determination of the Diffusive Halo Height
Pedro De la Torre Luque, Tim Linden
To Be Submitted to JCAP

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

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

63. Cosmic-Ray Propagation Models Elucidate the Prospects for Antinuclei Detection
Pedro De la Torre Luque, Martin Winkler, Tim Linden
To Be Submitted to JCAP

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

61. 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

60. Dark Matter Scattering Constraints from Observations of Stars Surrounding Sgr A*
Isabelle John, Rebecca Leane, Tim Linden
Accepted by Physical Review D

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

58. 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

57. 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)

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

55. 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

54. 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

53. 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)

52. 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)

51. 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

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

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
Physial Review Letters 129, 251102 (2022)

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

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
Physical Review Letters 131 7 071001

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)

Theses

Dark Matter Annihilation at the Galactic Center

Doctoral Thesis
13 June 2013

Tim Linden

Assistant Professor, Stockholm University

linden@fysik.su.se

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

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

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

Positron Annihilation in the Galaxy

Dark Matter Searches