Indirect Searches for Dark Photon-Photon Tridents in Celestial Objects
This paper models and constrains indirect dark matter detection signatures arising from dark photon trident decays in celestial objects, demonstrating that gamma-ray observations can provide stronger limits on dark matter-baryon scattering cross-sections than current direct detection methods and potentially penetrate the neutrino fog.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
For decades, scientists have been hunting for dark matter, the invisible substance that makes up most of the universe's mass but refuses to interact with light. While we cannot see it, we know it is there because its gravity holds galaxies together. To find it, researchers usually look for signs of dark matter particles crashing into ordinary matter or annihilating each other to produce flashes of light. Most of these searches have focused on simple, two-particle outcomes, like a dark matter particle turning into two photons. However, the universe is rarely that simple. There is a theoretical possibility that dark matter could interact through a hidden force, mediated by a particle called a "dark photon." If this dark photon is very light and long-lived, it might not decay immediately. Instead, it could travel a significant distance before breaking apart into three photons at once. This rare three-photon event, known as a trident, creates a unique signature that standard searches often miss, leaving a potential gap in our understanding of how dark matter behaves.
A new study by Tim Linden, Thong T.Q. Nguyen, and Tim M.P. Tait explores this specific scenario, asking what would happen if dark matter accumulated inside massive celestial bodies like planets, stars, and neutron stars. The researchers modeled a process where dark matter particles, drawn in by gravity, get trapped inside these objects. Once trapped, they collide and annihilate, creating the long-lived dark photons. Because these photons are so stable, they can escape the dense interior of the star or planet without being absorbed. Once they are far enough away in the vacuum of space, they finally decay into three photons. The team calculated exactly what this burst of light would look like and then compared their predictions against real data collected by powerful telescopes on Earth and in orbit.
The researchers focused on four specific targets: the Sun, Jupiter, brown dwarfs, and neutron stars. They reasoned that these objects act as natural traps, concentrating dark matter far more densely than exists in the empty space between stars. By analyzing data from the Fermi Large Area Telescope, the High Energy Stereoscopic System, and the High-Altitude Water Cherenkov Observatory, the team looked for the specific energy patterns that would result from these three-photon decays. They found that while no such signal has been detected yet, the absence of a signal allows them to set strict limits on how dark matter interacts with normal matter. Specifically, they calculated the maximum possible strength of the interaction between dark matter and atomic nuclei, a value known as the scattering cross-section.
The results reveal that looking at the sky can be more powerful than looking at the ground. For certain masses of dark matter, the constraints derived from observing Jupiter and the Sun are significantly tighter than those from the most sensitive underground detectors currently in operation. In fact, for very heavy dark matter particles, the limits set by observing neutron stars in the center of our galaxy are so strict that they begin to probe a region of physics where the signal from dark matter would be indistinguishable from the background noise created by neutrinos, a limit often called the "neutrino fog." This suggests that future observations of these celestial bodies could reach sensitivities that terrestrial experiments cannot yet achieve.
The study also highlights the importance of the specific energy of the light produced. The three-photon decay creates a distinct spectrum of gamma rays that differs from the more common two-particle decays. By mapping out this spectrum, the researchers showed that telescopes can distinguish between different types of dark matter interactions. They found that for lighter dark matter particles, observations of brown dwarfs and Jupiter are particularly effective, while for heavier particles, the intense gravity of neutron stars offers the best window into the physics. The team also noted that the survival of the dark photon depends heavily on its lifetime; if it decays too quickly, it vanishes inside the star, but if it lives too long, it might decay beyond the reach of our telescopes. Their calculations identified a narrow window where the dark photon lives just long enough to escape and decay in a detectable way.
Ultimately, this work demonstrates that the universe itself provides a laboratory for testing theories that are difficult to verify on Earth. By treating planets and stars as giant dark matter detectors, scientists can rule out vast ranges of possibilities for how dark matter might behave. The study does not claim to have found dark matter, but it has successfully narrowed the search, showing that if dark matter interacts with normal matter in this specific way, it must do so with a strength far weaker than previously thought possible for many mass ranges. This approach opens a new path for discovery, suggesting that the next breakthrough in understanding the invisible universe may come not from a new machine built in a lab, but from a more careful look at the light coming from the stars.
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