A new study Physical Examination Letters (PRL) proposed a new method for detecting obvious dark matter candidates by using laser interferometry to measure the oscillatory electric fields produced by these candidates. Dark matter is one of the most pressing problems in modern physics because dark matter particles are elusive and difficult to detect. This has led scientists to find new and innovative ways to find these particles.

There are several candidates for the role of dark matter particles, such as WIMPs, light dark matter particles (axions), and the hypothetical gravitino. Explicit dark matter, which contains bosonic particles such as the QCD (quantum chromodynamics) action, has become a subject of interest in recent years. These particles often have suppressed interactions with the standard model, making them difficult to detect. However, knowing their properties, including their wave-like behavior and coherent nature at galactic scales, helps design more efficient experiments.

In a new study PRL Researchers from the University of Maryland and Johns Hopkins University have proposed Galactic Axion Laser Interferometry Exploiting Electro-Optics, or GALILEO, a new approach to detect dark matter from both axions and dark photons over a wide mass range.

Principal investigator Reza Ebadi, a graduate student at the University of Maryland Quantum Technology Center (QTC), told Phys.org about the research and motivation for the development of this new approach: “While the Standard Model provides a successful explanation for phenomena varying from subnuclear distances, “Given the size of the universe, this is not a complete description of nature.”

“This does not take into account cosmological observations that conclude the existence of dark matter. Using small-scale laboratory experiments we aim to gain insight into physical theories operating at galactic scales.”

Axions and axion-like particles

Axion and axion-like particles were initially proposed to solve problems in particle physics, such as the strong charge coupling (CP) problem. This problem arises from the observation that the strong force does not exhibit a special type of symmetry breaking, called CP breaking, to the extent predicted by theory. This theoretical framework naturally gives rise to axion-like particles with similar properties as axions, both of which are bosons.

Axons and axion-like particles are assumed to have very low masses, typically in the microelectronvolt to millielectronvolt range. Because they can exhibit wave-like behavior on galactic scales, this makes them suitable candidates for open dark matter. In addition to their low mass, axons and axion-like particles interact very weakly with ordinary matter, making them difficult to detect by conventional methods.

These are some of the reasons why researchers decided to detect these particles in their experimental setups. However, the method relies on the oscillating electric fields created by these particles. In regions with significant dark matter density, axions and ALPs may undergo coherent oscillations. These coherent oscillations can produce detectable signals, such as the oscillatory electric fields that the proposed GALILEO experiment aims to measure.

GALILEO

“Luminous dark matter candidates behave like waves near the Sun. Such dark matter waves are predicted to cause very weak oscillating electric fields in conjunction with magnetic fields due to their small interactions with electromagnetism.”

“In most existing and proposed experiments, we focused on detecting the electric field rather than the magnetic field, which is the target signal,” Ebadi said.

Bright electric fields caused by dark matter can be detected using electro-optical materials, where an external electric field changes properties of the material, such as its refractive index.

GALILEO uses the asymmetric Michelson interferometer, a device that can measure changes in refractive index. One arm of the interferometer contains electro-optical material. When the probing laser beam is split and directed into two interferometer arms, the arm containing the electro-optical material creates a variable refractive index. This change in refractive index affects the phase of the laser beam and causes an oscillating signal when the beams recombine.

GALILEO can detect the frequency of oscillations caused by bright dark matter by measuring the differential phase velocity between the two arms of the interferometer. This oscillating signal is a sign of the presence of dark matter particles. The sensitivity of the method can be increased by the inclusion of Fabry-Perot gaps (this increases the length of the interferometer arm providing greater accuracy) and by making repeated independent measurements.

Application of laser interferometry and GALILEO

The research is based on precise measurements using laser interferometry. “The best example of how laser interferometers can be used for precise measurements is the ground-based gravitational wave detector LIGO,” Ebadi explained.

“Our proposal uses similar technological advances as LIGO, such as Fabry-Perot cavities or compressed light, to suppress the quantum noise limit. However, unlike LIGO, the proposed GALILEO interferometer is a benchtop device.”

Although the study is theoretical, the researchers already have plans for the phased implementation of the experimental program. More importantly, they want to determine the necessary technical parameters for an optimized experimental setup that they plan to use in scientific experiments to search for obvious dark matter.

Additionally, Ebadi emphasizes the importance of working with high-quality Fabry-Perot cavities as well as the electro-optical material inside the cavity, and describes the noise budget and setup systematics, which are important aspects of the experimental process.

“GALILEO has the potential to be a key component of a larger mission to explore the broad field of theoretically feasible dark matter candidates,” Ebadi said.