Dark matter remains one of the most pressing mysteries of modern physics since it is elusive and very difficult to detect. This has prompted experts to devise innovative ways to look for these strange particles.
(Photo: Wikimedia Commons/ Hubble ESA)
Dark Matter Candidates
Several candidates are involved in the search for dark matter particles, including weakly interacting massive particles (WIMPs) and the hypothetical gravitino. There are also light dark matter particles or axions, which include bosonic particles such as quantum chromo dynamics (QCD). The latter has become a point of interest among astronomers in recent years.
The light-dark matter particles are challenging to detect because they usually have suppressed interactions with the standard model. Still, scientists can design more efficient experiments by understanding their characteristics, like their wave-like behavior and coherent properties at galactic scales.
Axions and axionlike particles were initially thought to solve problems in particle physics, like the strong charge-parity (CP) problem. This challenge arises from the observation that the strong force does not seem to exhibit a particular type of symmetry violation as much as the theory predicts it should. Naturally, this theoretical framework gives rise to axionlike particles, which share similar characteristics to axions, with both being bosons.
Axions and axionlike particles are predicted to have shallow masses, ranging from microelectronvolts to millielectronvolts. This makes them ideal candidates for light-dark matter since they can exhibit wave-like behavior at galactic scales. Aside from their low mass, these particles also interact very weakly with ordinary matter, making them challenging to detect using conventional means.
Search for Light Dark Matter
In a collaborative study, experts from the University of Maryland and Johns Hopkins University have proposed the Galactic Axion Laser Interferometer Leveraging Electro-Optics (GALILEO). This novel approach could probe axion and dark photon dark matter over a wide range of mass.
Reza Ebadi from the Quantum Technology Center at the University of Maryland leads the study. The findings are discussed in the paper "GALILEO: Galactic Axion Laser Interferometer Leveraging Electro-Optics."
Light dark matter candidates have been found to behave as waves in the solar neighborhood. Due to their minuscule interactions with electromagnetism, such waves are assumed to induce fragile oscillating electric fields with magnetic fields.
Ebadi's team focused on detecting the electric field rather than the magnetic field since it is the target signal in most current and proposed experiments. Electric fields induced by light-dark matter can be detected using electro-optical materials, where the external electric field modifies their properties like a refractive index.
The team's experiment relies on precision measurement by laser interferometry. Their proposed GALILEO method uses similar technological advancements as LIGO but is a tabletop-scale device. GALILEO utilizes an asymmetric Michelson interferometer, which can measure changes in refractive index.
When a probe laser beam is split and sent through the interferometer's two arms, the arm containing the electro-optical material introduces a different refractive index. This change affects the phase of the laser beam, resulting in an oscillating signal when the beams are merged back together.
When the differential phase velocity between the interferometer's two arms is measured, GALILEO can detect the frequency of light-dark matter-induced oscillation. This oscillatory signal serves as the signature of the presence of dark matter particles.
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