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Scalar-mediated inelastic dark matter as a solution to small-scale structure anomalies

Zihan Wang*

  • *Contact author: zihan.wang@queens.ox.ac.uk
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Phys. Rev. D 113, 103015 – Published 11 May, 2026

DOI: https://doi.org/10.1103/lcbj-grg8

Abstract

We propose a novel self-interacting dark matter (SIDM) model mediated by a light leptophilic scalar boson to solve long-standing small-scale structure problems within the Lambda cold dark matter (ΛCDM) framework. Small-scale anomalies such as the core-cusp problem challenge the traditional CDM framework. Therefore, we introduce a scalar-mediated SIDM model as an alternative to CDM that naturally addresses these problems. It also exhibits p-wave-suppressed annihilation and avoids constraints from the cosmic microwave background. In our model, we assume pseudo-Dirac dark matter with a small mass splitting of order 102  eV to ensure kinematic scattering suppression in satellites. We also introduce a dimension-five transition magnetic dipole operator to satisfy big bang nucleosynthesis requirements. It allows the decay χ2→χ1γ, so the excited-state abundance is primarily depleted by exothermic self-interactions (χ2χ2→χ1χ1) in the early Universe. This ensures that the excited-state population is negligible for structure formation at the dipole scale Λeff≳107  GeV. The model is made inelastic by a dark discrete Z2 symmetry that prevents tree-level elastic scattering. Treating the scattering dynamics nonperturbatively in a Schrödinger framework yields a relatively small residual resonant benchmark window (mχ≈40  GeV, Δm≈100  eV, mϕ≈20  MeV). In such a system, the kinematic threshold minimizes interactions in ultrafaint Milky Way satellites, while resonant effects produce large cross sections, σ/m∼O(10)  cm2/g, in field dwarf galaxies. Current direct-detection prospects are weak, and the leptophilic scalar mediator keeps the model away from existing nuclear recoil constraints. However, the low-threshold dipole operator provides a potential discovery channel for future xenon-based experiments.

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References (78)

  1. N. Aghanim et al. (Planck Collaboration), Planck 2018 results. VI. Cosmological parameters, Astron. Astrophys. 641, A6 (2020); 652, C4(E) (2021).
  2. J. S. Bullock and M. Boylan-Kolchin, Small-scale challenges to the ΛCDM paradigm, Annu. Rev. Astron. Astrophys. 55, 343 (2017).
  3. V. Springel et al., Simulating the joint evolution of quasars, galaxies and their large-scale distribution, Nature (London) 435, 629 (2005).
  4. J. F. Navarro, C. S. Frenk, and S. D. M. White, A universal density profile from hierarchical clustering, Astrophys. J. 490, 493 (1997).
  5. S.-H. Oh, C. Brook, F. Governato, E. Brinks, L. Mayer, W. J. G. de Blok, A. Brooks, and F. Walter, The central slope of dark matter cores in dwarf galaxies: Simulations vs THINGS, Astron. J. 142, 24 (2011).
  6. B. Moore, Evidence against dissipationless dark matter from observations of galaxy haloes, Nature (London) 370, 629 (1994).
  7. W. J. G. de Blok, The core-cusp problem, Adv. Astron. 2010, 789293 (2010).
  8. K. A. Oman et al., The unexpected diversity of dwarf galaxy rotation curves, Mon. Not. R. Astron. Soc. 452, 3650 (2015).
  9. A. A. Klypin, A. V. Kravtsov, O. Valenzuela, and F. Prada, Where are the missing galactic satellites?, Astrophys. J. 522, 82 (1999).
  10. B. Moore, S. Ghigna, F. Governato, G. Lake, T. R. Quinn, J. Stadel, and P. Tozzi, Dark matter substructure within galactic halos, Astrophys. J. Lett. 524, L19 (1999).
  11. M. Boylan-Kolchin, J. S. Bullock, and M. Kaplinghat, Too big to fail? the puzzling darkness of massive Milky Way subhaloes, Mon. Not. R. Astron. Soc. 415, L40 (2011).
  12. S. Garrison-Kimmel, M. Boylan-Kolchin, J. S. Bullock, and E. N. Kirby, Too big to fail in the local group, Mon. Not. R. Astron. Soc. 444, 222 (2014).
  13. D. N. Spergel and P. J. Steinhardt, Observational evidence for selfinteracting cold dark matter, Phys. Rev. Lett. 84, 3760 (2000).
  14. S. Tulin and H.-B. Yu, Dark matter self-interactions and small scale structure, Phys. Rep. 730, 1 (2018).
  15. M. Rocha, A. H. G. Peter, J. S. Bullock, M. Kaplinghat, S. Garrison-Kimmel, J. Onorbe, and L. A. Moustakas, Cosmological simulations with self-interacting dark matter I: Constant density cores and substructure, Mon. Not. R. Astron. Soc. 430, 81 (2013).
  16. A. H. G. Peter, M. Rocha, J. S. Bullock, and M. Kaplinghat, Cosmological simulations with self-interacting dark matter II: Halo shapes vs. observations, Mon. Not. R. Astron. Soc. 430, 105 (2013).
  17. A. Kamada, M. Kaplinghat, A. B. Pace, and H.-B. Yu, How the self-Interacting dark matter model explains the diverse galactic rotation curves, Phys. Rev. Lett. 119, 111102 (2017).
  18. C. A. Correa, Constraining velocity-dependent self-interacting dark matter with the Milky Way’s dwarf spheroidal galaxies, Mon. Not. R. Astron. Soc. 503, 920 (2021).
  19. M. Markevitch, A. H. Gonzalez, D. Clowe, A. Vikhlinin, L. David, W. Forman, C. Jones, S. Murray, and W. Tucker, Direct constraints on the dark matter self-interaction cross-section from the merging galaxy cluster 1E0657-56, Astrophys. J. 606, 819 (2004).
  20. S. W. Randall, M. Markevitch, D. Clowe, A. H. Gonzalez, and M. Bradac, Constraints on the self-interaction cross-section of dark matter from numerical simulations of the merging galaxy cluster 1E 0657-56, Astrophys. J. 679, 1173 (2008).
  21. D. Harvey, R. Massey, T. Kitching, A. Taylor, and E. Tittley, The non-gravitational interactions of dark matter in colliding galaxy clusters, Science 347, 1462 (2015).
  22. J. H. O’Donnell, T. E. Jeltema, M. G. Roberts, J. Nightingale, A. Flowers, and D. Aldas, A constraint on dark matter Self-Interaction from combined strong lensing and stellar kinematics in MACS J0138-2155, Phys. Rev. D 113, 063531 (2026).
  23. J. Zavala, M. Vogelsberger, and M. G. Walker, Constraining self-interacting dark matter with the Milky Way’s dwarf spheroidals, Mon. Not. R. Astron. Soc. 431, L20 (2013).
  24. M. Valli and H.-B. Yu, Dark matter self-interactions from the internal dynamics of dwarf spheroidals, Nat. Astron. 2, 907 (2018).
  25. H. Nishikawa, K. K. Boddy, and M. Kaplinghat, Accelerated core collapse in tidally stripped self-interacting dark matter halos, Phys. Rev. D 101, 063009 (2020).
  26. S. Tulin, H.-B. Yu, and K. M. Zurek, Beyond collisionless dark matter: Particle physics dynamics for dark matter halo structure, Phys. Rev. D 87, 115007 (2013).
  27. D. Tucker-Smith and N. Weiner, Inelastic dark matter, Phys. Rev. D 64, 043502 (2001).
  28. T. R. Slatyer, The sommerfeld enhancement for dark matter with an excited state, J. Cosmol. Astropart. Phys. 02 (2009) 028.
  29. N. Arkani-Hamed, D. P. Finkbeiner, T. R. Slatyer, and N. Weiner, A theory of dark matter, Phys. Rev. D 79, 015014 (2009).
  30. T. R. Slatyer, Indirect dark matter signatures in the cosmic dark ages. I. Generalizing the bound on s-wave dark matter annihilation from Planck results, Phys. Rev. D 93, 023527 (2016).
  31. L. Lopez-Honorez, O. Mena, S. Palomares-Ruiz, and A. C. Vincent, Constraints on dark matter annihilation from CMB observationsbefore Planck, J. Cosmol. Astropart. Phys. 07 (2013) 046.
  32. D. E. Kaplan, M. A. Luty, and K. M. Zurek, Asymmetric dark matter, Phys. Rev. D 79, 115016 (2009).
  33. K. Petraki and R. R. Volkas, Review of asymmetric dark matter, Int. J. Mod. Phys. A 28, 1330028 (2013).
  34. M. Vogelsberger, J. Zavala, and A. Loeb, Subhaloes in self-interacting galactic dark matter haloes, Mon. Not. R. Astron. Soc. 423, 3740 (2012).
  35. C. Garcia-Cely, A. Ibarra, and E. Molinaro, Dark matter production from Goldstone boson interactions and implications for direct searches and dark radiation, J. Cosmol. Astropart. Phys. 11 (2013) 061.
  36. A. Berlin, J. W. Foster, D. Hooper, and G. Krnjaic, dSphobic dark matter, J. Cosmol. Astropart. Phys. 04 (2026) 017.
  37. S. Knapen, T. Lin, and K. M. Zurek, Light dark matter: Models and constraints, Phys. Rev. D 96, 115021 (2017).
  38. J. Aalbers et al. (LZ Collaboration), First dark matter search results from the LUX-ZEPLIN (LZ) experiment, Phys. Rev. Lett. 131, 041002 (2023).
  39. E. Aprile et al. (XENON Collaboration), WIMP dark matter search using a 3.1 tonne-year exposure of the XENONnT experiment, Phys. Rev. Lett. 135, 221003 (2025).
  40. Z. Bo et al. (PandaX Collaboration), Dark matter search results from 1.54 tonne·year exposure of PandaX-4T, Phys. Rev. Lett. 134, 011805 (2025).
  41. G. C. Branco, P. M. Ferreira, L. Lavoura, M. N. Rebelo, M. Sher, and J. P. Silva, Theory and phenomenology of two-Higgs-doublet models, Phys. Rep. 516, 1 (2012).
  42. K. Sigurdson, M. Doran, A. Kurylov, R. R. Caldwell, and M. Kamionkowski, Dark-matter electric and magnetic dipole moments, Phys. Rev. D 70, 083501 (2004).
  43. P. F. Depta, M. Hufnagel, and K. Schmidt-Hoberg, Robust cosmological constraints on axion-like particles, J. Cosmol. Astropart. Phys. 05 (2020) 009.
  44. K. Schutz and T. R. Slatyer, Self-scattering for dark matter with an excited state, J. Cosmol. Astropart. Phys. 01 (2015) 021.
  45. H. An, M. B. Wise, and Y. Zhang, Effects of bound states on dark matter annihilation, Phys. Lett. B 773, 121 (2017).
  46. J. Hisano, S. Matsumoto, and M. M. Nojiri, Explosive dark matter annihilation, Phys. Rev. Lett. 92, 031303 (2004).
  47. S. Ando, K. Hayashi, S. Horigome, M. Ibe, and S. Shirai, Stringent constraints on self-interacting dark matter using milky-way satellite galaxies kinematics, arXiv:2503.13650.
  48. C. A. Correa, Constraining velocity-dependent self-interacting dark matter with the Milky Way’s dwarf spheroidal galaxies, Mon. Not. R. Astron. Soc. 503, 920 (2021).
  49. A. Parikh, R. Sato, and T. R. Slatyer, Regulating sommerfeld resonances for multi-state systems and higher partial waves, J. High Energy Phys. 12 (2024) 025.
  50. K. Blum, R. Sato, and T. R. Slatyer, Self-consistent calculation of the sommerfeld enhancement, J. Cosmol. Astropart. Phys. 06 (2016) 021.
  51. K. Petraki, M. Postma, and J. de Vries, Radiative bound-state-formation cross-sections for dark matter interacting via a Yukawa potential, J. High Energy Phys. 04 (2016) 077.
  52. J. Beacham et al., Physics beyond colliders at CERN: Beyond the standard model working group report, J. Phys. G 47, 010501 (2020).
  53. J. P. Lees et al. (BABAR Collaboration, Search for a dark photon in e+e− collisions at BABAR, Phys. Rev. Lett. 113, 201801 (2014).
  54. D. Banerjee et al., Dark matter search in missing energy events with NA64, Phys. Rev. Lett. 123, 121801 (2019).
  55. T. Åkesson et al. (LDMX Collaboration), Light dark matter eXperiment (LDMX), arXiv:1808.05219.
  56. T. Binder, L. Covi, A. Kamada, K. Murai, T. Takahashi, and N. Yoshida, Matter power spectrum in hidden neutrino interacting dark matter models: A general treatment, J. Cosmol. Astropart. Phys. 11 (2016) 043.
  57. C. Boehm, P. Fayet, and R. Schaeffer, Constraining dark matter candidates from structure formation, Phys. Lett. B 518, 8 (2001).
  58. J. H. Chang, R. Essig, and S. D. McDermott, Supernova 1987A constraints on sub-GeV dark sectors, millicharged particles, the QCD axion, and an axion-like particle, J. High Energy Phys. 09 (2018) 051.
  59. G. G. Raffelt, Stars as Laboratories for Fundamental Physics: The Astrophysics of Neutrinos, Axions, and Other Weakly Interacting Particles (University of Chicago Press, Chicago, IL, 1996).
  60. C. Boehm and P. Fayet, Scalar dark matter candidates, Nucl. Phys. B683, 219 (2004).
  61. J. Chluba and R. A. Sunyaev, The evolution of CMB spectral distortions in the early universe, Mon. Not. R. Astron. Soc. 419, 1294 (2012).
  62. V. Poulin, J. Lesgourgues, and P. D. Serpico, Cosmological constraints on exotic injection of electromagnetic energy, J. Cosmol. Astropart. Phys. 03 (2016) 043.
  63. S. O’Neil et al., Endothermic self-interacting dark matter in Milky Way-like dark matter haloes, Mon. Not. R. Astron. Soc. 524, 288 (2023).
  64. P. De la Torre Luque, P. Carenza, and T. T. Q. Nguyen, Sub-keV dark matter can strongly ionize molecular clouds, Phys. Rev. D 113, 063035 (2026).
  65. D. Agius and T. R. Slatyer, Boosting the cosmic 21-cm signal with exotic Lyman-α from dark matter, arXiv:2510.26791.
  66. G. Krnjaic, D. McKeen, R. Mizuta, G. Mohlabeng, D. E. Morrissey, and D. Tuckler, X-rays from inelastic dark matter Freeze-in, Phys. Rev. D 112, 115039 (2025).
  67. E. Hardy and R. Lasenby, Stellar cooling bounds on new light particles: Plasma mixing effects, J. High Energy Phys. 02 (2016) 033.
  68. Y.-S. Liu, D. McKeen, and G. A. Miller, Electrophobic scalar boson and muonic puzzles, Phys. Rev. Lett. 117, 101801 (2016).
  69. R. H. Cyburt, B. D. Fields, K. A. Olive, and T.-H. Yeh, Big bang nucleosynthesis: 2015, Rev. Mod. Phys. 88, 015004 (2016).
  70. J. Kopp, L. Michaels, and J. Smirnov, Loopy constraints on leptophilic dark matter and internal bremsstrahlung, J. Cosmol. Astropart. Phys. 04 (2014) 022.
  71. E. Aprile et al. (XENON Collaboration), Search for new physics in electronic recoil data from XENONnT, Phys. Rev. Lett. 129, 161805 (2022).
  72. J. Aalbers et al. (LZ Collaboration), Search for new physics in low-energy electron recoils from the first LZ exposure, Phys. Rev. D 108, 072006 (2023).
  73. S. Chang, N. Weiner, and I. Yavin, Magnetic inelastic dark matter, Phys. Rev. D 82, 125011 (2010).
  74. A. L. Fitzpatrick, W. Haxton, E. Katz, N. Lubbers, and Y. Xu, The effective field theory of dark matter direct detection, J. Cosmol. Astropart. Phys. 02 (2012) 004.
  75. Y. F. Bautista, A. Robertson, L. Sagunski, A. Smith-Orlik, and S. Tulin, Jeans model for the shapes of self-interacting dark matter halos, arXiv:2511.10765.
  76. T. Bringmann, F. Kahlhoefer, K. Schmidt-Hoberg, and P. Walia, Strong constraints on self-interacting dark matter with light mediators, Phys. Rev. Lett. 118, 141802 (2017).
  77. Y. Cui and F. D’Eramo, Surprises from complete vector portal theories: New insights into the dark sector and its interplay with Higgs physics, Phys. Rev. D 96, 095006 (2017).
  78. J. Aalbers et al. (XLZD Collaboration), The XLZD design book: Towards the next-generation liquid xenon observatory for dark matter and neutrino physics, Eur. Phys. J. C 85, 1192 (2025).

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Phys. Rev. D 113, 103015– Published 11 May, 2026
  • Received 23 December 2025
  • Accepted 16 April 2026
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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.

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