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Dark matter: red or blue?

A. Acar, C. Isaacson, M. Bashkanov, D. P. Watts

TL;DR

This work provides the first Standard Model-based calculation of light scattering off heavy dark matter, considering both weakly interacting and purely gravitational DM. It demonstrates that photons can scatter off DM via loop-induced Higgs/W interactions or graviton exchange, producing nonzero cross sections with distinct energy and angular dependences, as well as polarization effects. The weakly interacting channel exhibits backward-dominated scattering and a measurable cross section around $\sim$100 fb for $M_\chi \sim 1$ TeV, while the gravitational channel favors forward scattering and blue spectral coloring, albeit with smaller flux-based observability. Using Fermi-LAT data and an NFW DM profile, the study places an upper limit $M_\chi < 5.0 \times 10^{19}$ GeV on heavy DM and highlights polarization measurements as a potentially powerful probe for discriminating DM interaction types, motivating future high-precision gamma-ray observations in dense DM environments.

Abstract

We report the first calculation of light scattering on heavy dark matter (DM) particles. We show that despite the fact that DM has no direct coupling to photons, the light-DM($γχ$) ($m_χ\sim 1$ TeV) cross-section is non-vanishing, albeit small. The cross section, calculated within the Standard Model (SM) framework, is particularly large in the case of heavy Weakly Interacting Massive Particles (WIMP). Combined with astrophysical observation, these results can constrain existing WIMP DM models in favor of lighter DM, $M_χ<<M_{\mathrm{Planck}}$, (axions, composite DM, etc..) or non-weakly interacting pure gravitational DM. We also show that the energy dependence of light scattering on dark matter should make the DM colored - red in the case of weak-DM and blue for the gravitational-DM, when a white background light is passing through. Gravitational scattering of light on DM particles also leads to non-trivial polarization effects, which might be easier to detect than the deflection of light from the scattering on DM particles, $γχ\rightarrowγχ$.

Dark matter: red or blue?

TL;DR

This work provides the first Standard Model-based calculation of light scattering off heavy dark matter, considering both weakly interacting and purely gravitational DM. It demonstrates that photons can scatter off DM via loop-induced Higgs/W interactions or graviton exchange, producing nonzero cross sections with distinct energy and angular dependences, as well as polarization effects. The weakly interacting channel exhibits backward-dominated scattering and a measurable cross section around 100 fb for TeV, while the gravitational channel favors forward scattering and blue spectral coloring, albeit with smaller flux-based observability. Using Fermi-LAT data and an NFW DM profile, the study places an upper limit GeV on heavy DM and highlights polarization measurements as a potentially powerful probe for discriminating DM interaction types, motivating future high-precision gamma-ray observations in dense DM environments.

Abstract

We report the first calculation of light scattering on heavy dark matter (DM) particles. We show that despite the fact that DM has no direct coupling to photons, the light-DM() ( TeV) cross-section is non-vanishing, albeit small. The cross section, calculated within the Standard Model (SM) framework, is particularly large in the case of heavy Weakly Interacting Massive Particles (WIMP). Combined with astrophysical observation, these results can constrain existing WIMP DM models in favor of lighter DM, , (axions, composite DM, etc..) or non-weakly interacting pure gravitational DM. We also show that the energy dependence of light scattering on dark matter should make the DM colored - red in the case of weak-DM and blue for the gravitational-DM, when a white background light is passing through. Gravitational scattering of light on DM particles also leads to non-trivial polarization effects, which might be easier to detect than the deflection of light from the scattering on DM particles, .

Paper Structure

This paper contains 10 sections, 77 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Weak Interactions
  3. Gravitational Interactions
  4. Results
  5. Summary
  6. Acknowledgements
  7. Appendix
  8. Gravitationally and Weakly Interacting Dark Matter
  9. Weakly Interacting DM
  10. Gravitationally Interacting DM

Figures (8)

  • Figure 1: All possible diagrams for dark matter-photon scattering propagated by the Higgs boson and Graviton in the unitary gauge.
  • Figure 2: Angular(left) and Energy(right) dependence of the differential cross section for photons scattering on $M_{\chi}=1$ TeV WIMP dark matter particles for fixed photon energies of 1 GeV(blue solid), 50 GeV(violet long-dash), 500 GeV(red dash-dot-dot) and 800 GeV(pink short-dash) and fixed photon angles 10 deg (blue solid), 60 deg (red dash-dot-dot), 90 deg(violate long-dash) and 180 deg (pink short dash).
  • Figure 3: Differential cross-sections for photons scattered on 1 TeV WIMP dark matter particles as a function of photon energy(x-axis) and scattering photon angle (y-axis).
  • Figure 4: The total $\gamma\chi$ scattering cross section alongside with the individual contributions from fermion and W loops for the $M_\chi=1$ TeV.
  • Figure 5: The differential $\gamma\chi$ scattering cross section via gravitational interaction for the $M_\chi=10^{19}$ GeV as a function of photon scattering angle for two photon polarisations. (Note the $10^{247}$ scale)
  • ...and 3 more figures