Direct Detection Constraints on Dark Photon Dark Matter (1412.8378v3)

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 $V\to 3\gamma$ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse gamma-ray flux.

• The paper demonstrates that direct detection experiments can constrain dark photon DM by analyzing unique ionization signals to set mixing angle limits as low as 10⁻¹⁵.
• The methodology exploits absorption processes in vector dark matter, offering enhanced sensitivity compared to traditional elastic scattering and stellar energy loss limits.
• The study integrates astrophysical and cosmological analyses, reinforcing the viability of dark photon models and guiding future experimental and theoretical explorations.

Direct Detection Constraints on Dark Photon Dark Matter: An Analysis

The research paper titled "Direct Detection Constraints on Dark Photon Dark Matter" addresses the exploration of dark photon models within the context of dark matter (DM) direct detection efforts. Authored by Haipeng An, Maxim Pospelov, Josef Pradler, and Adam Ritz, this work provides a detailed theoretical and experimental assessment of the sensitivity of current direct detection experiments to a minimal model of dark photon dark matter. The paper ranges over the mass window of $0.01-100$ keV for dark photons.

The concept of dark photons arises from extensions to the Standard Model (SM) that incorporate an additional $U(1)'$ gauge symmetry. The dark photon, denoted as $V$, acquires a small mixing angle $\kappa$ with the SM photon, allowing it to interact weakly with ordinary matter. This model stands as a potential solution to the dark matter enigma, addressing a compelling gap in our understanding of cosmological and particle physics phenomena.

Key Results and Methodological Insights

Direct Detection and Constraints: The central contribution of this paper lies in evaluating the ability of direct detection experiments, specifically XENON10 and XENON100, to constrain the parameter space of dark photon models. By investigating the ionization signals from potential dark photon interactions with detector materials, the authors derive new constraints on the mixing angle $\kappa$ for a significant fraction of the considered mass range. Notably, these experiments show sensitivity to $\kappa \sim \mathcal{O}(10^{-15})$, which surpasses the bounds derived from stellar energy loss for certain mass regimes. This sensitivity expansion does not rely on traditional elastic scattering mechanisms but rather on absorption processes unique to vectorial DM candidates.

Stellar and Cosmological Considerations: The work also revisits constraints on dark photon mixing from indirect limits, including energy loss processes in stars such as the Sun and horizontal branch (HB) stars. Using sophisticated models of these astrophysical environments, the authors reaffirm constraints that are mass-dependent, illustrating a robustness in stellar-based exclusion limits up to $10^3$ eV. Furthermore, decay processes like $V \to 3\gamma$ are included to consider impacts on the diffuse gamma-ray background as well as potential alterations to the cosmological ionization history. Both constraints yield limits on $\kappa$ on par with direct detection findings.

Theoretical Implications and Future Directions

The work underscores the importance of kinetic mixing models and highlights vector fields as viable candidates in the ongoing search for DM. By demonstrating how non-thermal production mechanisms, like inflationary perturbations, could yield dark photon DM consistent with observational data, the paper suggests intriguing pathways for cosmological model-building. The results prompt further exploration into enhanced sensitivity methodologies, particularly for detecting ionization signals from sub-keV photon masses.

Future developments in this avenue may include refined cross-sectional calculations for photon absorption incorporating dark photon effects and expanding the parameter space to incorporate related models or extensions, such as pseudoscalar dark matter or tensor couplings with electrons. Furthermore, a more thorough engagement with atomic physics may enhance the precision of observational data analysis in ionization-sensitive environments, thereby tightening constraints further.

In conclusion, the research offers a crucial advancement in the theoretical and empirical assessment of dark photon dark matter, enriching our understanding of potential interplays between classical and novel physics paradigms. This work paves the way for further interdisciplinary dialogue, bridging gaps between astrophysical observations, high-energy physics, and cosmological models, while providing concrete avenues for future theoretical and experimental advancements.