Dark Matter Direct Detection Experiments Are Sensitive to the Millicharged Background.

Area of Science:

• Particle Physics
• Cosmology
• Astrophysics

Background:

• Direct detection experiments search for dark matter particles interacting with ordinary matter.
• Current searches primarily focus on WIMP candidates with significant interaction cross-sections.
• Alternative dark matter candidates and detection strategies are crucial for comprehensive exploration.

Purpose of the Study:

• To investigate the sensitivity of dark matter direct detection experiments to particles with small effective charges.
• To explore the potential of these experiments to detect dark matter sub-fractions produced via the freeze-in mechanism.
• To forecast the reach of ongoing and proposed experiments for these novel dark matter candidates.

Main Methods:

• Utilizing theoretical framework for dark matter interactions with small effective charges, including couplings to dark photons.
• Modeling the freeze-in production mechanism in the early Universe to determine irreducible dark matter abundance.
• Simulating the sensitivity reach of current and future direct detection experiments based on predicted signal characteristics.

Main Results:

• Demonstrating that direct detection experiments are sensitive to particles with effective charges as low as Q∼10^{-12}.
• Establishing that this sensitivity extends across 9 orders of magnitude in particle mass.
• Showing that experiments can probe dark matter sub-fractions down to ∼10^{-3} of the total dark matter abundance.

Conclusions:

• Dark matter direct detection experiments possess significant, often world-leading, sensitivity to a broad range of dark matter candidates beyond traditional WIMPs.
• The freeze-in mechanism provides a viable production pathway for detectable dark matter sub-fractions.
• Future direct detection efforts will play a pivotal role in exploring parameter space for light, weakly interacting particles.