Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Direct Detection Constraints on Dark Photon Dark Matter

Haipeng An, Maxim Pospelov, Josef Pradler, Adam Ritz

TL;DR

The paper investigates dark photon dark matter with mass $m_V$ in the window $0.01$--$100$ keV and kinetic mixing $\kappa$ with the Standard Model. It develops the dark photon DM framework, accounts for in-medium dispersion and production mechanisms (including inflationary misalignment), and derives absorption rates of dark photons in xenon detectors, linking the signal to the local DM density via $\Gamma_{abs} \simeq (\rho_{DM}/m_V c^2) \kappa^2 \sigma_\gamma(\omega=m_V) c$. By combining cosmological/stellar bounds (including $V\to 3\gamma$) with direct-detection analyses of XENON10 and XENON100, the study achieves direct-detection constraints on $\kappa$ down to $\mathcal{O}(10^{-15})$ for certain $m_V$, often surpassing stellar bounds in the same mass range. The results demonstrate that existing WIMP-search experiments can substantially probe ultra-weakly coupled, light DM and highlight non-thermal production scenarios, such as inflationary perturbations, as viable avenues for achieving the observed relic density. The work also points to practical improvements via ionization-only analyses and Auger processes in future detectors, broadening the reach of direct-detection searches for light vector dark matter.

Abstract

Dark matter detectors built primarily to probe elastic scattering of WIMPs on nuclei are also precise probes of light, weakly coupled particles that may be absorbed by the detector material. In this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states V (dark photons) in the 0.01-100 keV mass range. The absence of an ionization signal in direct detection experiments such as XENON10 and XENON100 places a very strong constraint on the dark photon mixing angle, down to $O(10^{-15})$, assuming that dark photons comprise the dominant fraction of dark matter. This sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. We also revisit indirect constraints from $V\to 3γ$ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse gamma-ray flux.

Direct Detection Constraints on Dark Photon Dark Matter

TL;DR

The paper investigates dark photon dark matter with mass in the window -- keV and kinetic mixing with the Standard Model. It develops the dark photon DM framework, accounts for in-medium dispersion and production mechanisms (including inflationary misalignment), and derives absorption rates of dark photons in xenon detectors, linking the signal to the local DM density via . By combining cosmological/stellar bounds (including ) with direct-detection analyses of XENON10 and XENON100, the study achieves direct-detection constraints on down to for certain , often surpassing stellar bounds in the same mass range. The results demonstrate that existing WIMP-search experiments can substantially probe ultra-weakly coupled, light DM and highlight non-thermal production scenarios, such as inflationary perturbations, as viable avenues for achieving the observed relic density. The work also points to practical improvements via ionization-only analyses and Auger processes in future detectors, broadening the reach of direct-detection searches for light vector dark matter.

Abstract

Dark matter detectors built primarily to probe elastic scattering of WIMPs on nuclei are also precise probes of light, weakly coupled particles that may be absorbed by the detector material. In this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states V (dark photons) in the 0.01-100 keV mass range. The absence of an ionization signal in direct detection experiments such as XENON10 and XENON100 places a very strong constraint on the dark photon mixing angle, down to , assuming that dark photons comprise the dominant fraction of dark matter. This sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. We also revisit indirect constraints from decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse gamma-ray flux.

Paper Structure

This paper contains 10 sections, 22 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Dark photon dark matter
  3. Cosmological abundance
  4. Stellar dark photon constraints
  5. Constraints from $V\to 3\gamma$ decay
  6. DM absorption signals in direct detection experiments
  7. Dark vector-induced ionization
  8. XENON10
  9. XENON100
  10. Discussion and Conclusion

Figures (3)

  • Figure 1: A summary of constraints on the dark photon kinetic mixing parameter $\kappa$ as a function of vector mass $m_V$ (see Secs. \ref{['sec:dark-photon-dark']} and \ref{['sec:dm-absorpt-sign']} for the details). The thick lines exclude the region above for dark photons with dark matter relic density. The solid (dashed) line is from XENON10 (XENON100); the limit from XMASS is taken from Abe:2014zcd. The dash-dotted lines show our newly derived constraints on the diffuse $\gamma$-ray flux from $V\to 3\gamma$ decays, assuming that decays contribute 100% (thick line) or 10% (thin line) to the observed flux. The thick dotted line is the corresponding constraint from CMB energy injection. Shaded regions depict (previously considered) astrophysical constraints that are independent of the dark photon relic density. The limits from anomalous energy loss in the sun (sun), horizontal branch stars (HB), and red giant stars (RG) are labeled. The shaded region that is mostly inside the solar constraint is the XENON10 limit derived from the solar flux An:2013yua.
  • Figure 2: Representative diffuse gamma ray bolometric flux (thick solid top line) together with computed extragalactic (galactic) photon fluxes depicted by the dashed (dotted) line from $V\to 3\gamma$ decay. We constrain the sum of these fluxes (solid line) to not exceed the observed one.
  • Figure 3: Left: Real and imaginary parts of the liquid xenon refractive index computed from tabulated atomic scattering factors and using the Kronig-Kramers relation. Note that the maximum of the $\mathop{\mathrm{Im}}\nolimits (n)$ function corresponds to the photoelectric cross section $\sigma_\gamma \sim 6\times 10^{-17}{\rm cm}^2$. Right: Simulated events in 'xenon-units' of photo-electrons (PE) for various dark photon masses as labeled. Also shown are the reported event counts and the background model as taken from Aprile:2014eoa.