Dark Photon Dark Matter Produced by Axion Oscillations (1810.07196v2)

Abstract: Despite growing interest and extensive effort to search for ultralight dark matter in the form of a hypothetical dark photon, how it fits into a consistent cosmology is unclear. Several dark photon dark matter production mechanisms proposed previously are known to have limitations, at least in certain mass regimes of experimental interest. In this letter, we explore a novel mechanism, where a coherently oscillating axion-like field can efficiently transfer its energy density to a dark photon field via a tachyonic instability. The residual axion relic is subsequently depleted via couplings to the visible sector, leaving only the dark photon as dark matter. We ensure that the cosmologies of both the axion and dark photon are consistent with existing constraints. We find that the mechanism works for a broad range of dark photon masses, including those of interest for ongoing experiments and proposed detection techniques.

• The paper introduces a novel cosmological mechanism where a coherently oscillating axion-like field transfers energy efficiently to a dark photon field via tachyonic instability.
• Numerical simulations validate the model's cosmological viability for dark photon masses over a wide range, consistent with constraints like warm dark matter.
• This production mechanism provides theoretical support for dark photon detection experiments and suggests potential links between axion and dark photon dynamics.

Dark Photon Dark Matter Produced by Axion Oscillations

The exploration of dark matter candidates extends continually as researchers attempt to unravel the complexities of our universe. One intriguing candidate is the dark photon, a hypothetical gauge boson manifesting through minuscule couplings with the Standard Model (SM). The paper "Dark Photon Dark Matter Produced by Axion Oscillations," co-authored by Raymond T. Co, Aaron Pierce, Zhengkang Zhang, and Yue Zhao, presents an innovative mechanism for producing dark photon dark matter (DPDM) within a cosmological framework.

Summary of the Mechanism

The transition from theoretical speculation to experimental investigation requires a coherent cosmological mechanism for DPDM production. Traditional mechanisms face limitations, particularly in certain mass regimes. The paper introduces a mechanism where a coherently oscillating axion-like field mediates the efficient transfer of its energy density to a dark photon field through a tachyonic instability. This process ensures the depletion of the residual axion relic by subsequent couplings to the visible sector, reconciling the cosmologies of both the axion and the dark photon with existing constraints.

The researchers focus on the coupling of an axion-like particle $\phi$ with a dark photon $A'$, expressed as $\phi F_{\mu\nu}'\tilde{F}^{\mu\nu}'$, which facilitates the conversion of energy density into the dark photon field. The key lies in the tachyonic instability, a phenomenon where the effective mass becomes negative, leading to the exponential growth of specific field modes. This mechanism balances the need for efficient production without necessitating stringent fine-tuning of parameters.

Validation and Constraints

Numerical simulations confirm the validity of the model within various parameter ranges. The paper emphasizes the cosmological viability for dark photon masses over a wide range, accommodating the mass interests of ongoing experiments. Key considerations include consistency with constraints on warm dark matter and the presence of isocurvature perturbations.

The thermal history of the universe plays a critical role in the proposed mechanism, with the paper distinguishing between matter-dominated and radiation-dominated scenarios. In each case, the thermalization of the remaining axion relic is crucial, achieved through couplings to the SM—particularly to hypercharge gauge bosons. This coupling, dependent on the axion and dark photon health at different epochs, underscores the complexity of establishing a self-consistent cosmological model.

Implications and Speculations

The potential detection of dark photons through experiments interfaced with accelerometers, dish antennas, dielectric haloscopes, and radio frequencies gains enhanced substantiation by this mechanism. Future experimental data, challenging constraints on the parameter space, might reveal possible signatures of the axion and dark photon interaction dynamics.

Moreover, the paper suggests that discoveries related to PQ fermions may significantly impact the understanding of the PQ scale in cosmology. These fermionic candidates hint at observable consequences in collider experiments, rendering a multitude of testable predictions in symbiosis with this proposed model.

Conclusion

This paper provides an essential theoretical advancement in dark matter research, offering a physics-grounded mechanism to anchor dark photons as viable candidates. By addressing production and cosmological sustainability through axion oscillations, the framework contributes substantively to the underlying narrative of a substantial cosmological epoch. This not only enriches the landscape of dark photon studies within theoretical physics but also propels the dialogue towards experimental verifications and future investigations within the field of particle physics and cosmology.