New work has recently opened up a new standard for how to hunt for inelastic dark matter particles. This major breakthrough represents an important step toward unravelling the mysteries of one of the universe’s most elusive constituents. Currently, dark matter is thought to account for 27% of the total mass-energy content of the universe. Even though scientists are confident it exists, we know very little about it. This enigmatic material combines with dark energy, which constitutes roughly 68% of the universe, to shape the cosmos. These two unknown components stretch the limits of our current scientific understanding beyond recognition.
The ongoing search for dark matter particles is critical since all known matter constitutes only about 5% of the universe’s content. Now, an international collaboration of scientists has determined the properties of a stable particle χ₁. They’ve discovered an even heavier and unstable particle called χ₂. The nature of the interaction between these particles is important for detection in experiments. Moving from χ₁ to χ₂ comes with much greater obstacles. This transformation is further complicated by the mass difference between the two particles, rendering direct detection a challenge.
The model they have proposed for dark matter relies on a generalized vector mediator that they have dubbed ZQ. This new mediator actively facilitates interactions between dark matter and standard model particles. Such an unconventional approach could lead to exciting new directions for exploring the properties of dark matter and for sharpening our detection methods.
Understanding Dark Matter and Its Components
Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter. Inertia (dark matter) makes up for around 27% of the total mass-energy content of the universe. Note that meanwhile, dark energy accounts for roughly 68% of it. By contrast, regular matter—stars, planets, and galaxies—makes up just 5%.
Researchers have identified two primary types of dark matter particles: a stable particle (χ₁) and an unstable particle (χ₂). Though χ₁ is theorized to be stable, χ₂, the heavier of the two, is unstable and decays into various products. In order for χ₁ to be observed in direct detection experiments, it needs to make a transition into χ₂. This transformation—the only uncharged transformation there is—is limited by the huge mass difference between the two particles.
“Despite knowing with a high degree of certainty that dark matter exists, we do not (yet) know what it is.” – Ralf Kaehler / SLAC National Accelerator Laboratory
This lack of certainty underscores the challenges that researchers face. Their work is ongoing in finding ways to detect and research dark matter.
The Role of Vector Mediators
Recent studies suggest a promising new alternative, though. It introduces a vector boson, ZQ, which mediates interactions between the dark matter sector and the visible sector. This vector mediator turns out to be key to its role in connecting particle interactions. Furthermore, because ZQ mediator interactions cause the particles to interact collectively, this increases the interactions’ potential for detection in experiments.
In their new study, researchers determined the abundance of dark matter by modeling its freeze-out process. They released their code publicly demonstrating the same calculations, letting anyone else reproduce these calculations. This code is intended to illuminate other regions of parameter space that produce inelastic dark matter with other conditions. Figuring out these, often hidden, regions is imperative for seeing these rare, elusive particles.
“The use of more general vector mediators opens a new window for viable models of inelastic DM, with direct consequences for decay rates, experimental signatures, and cosmological limits.” – Renata Zukanovich Funchal
The study sheds light on the new theory’s unique ability to provide a better understanding of dark matter production and detection. It does this by interactions that are mediated by the so-called ZQ particle.
Overcoming Detection Challenges
Detecting dark matter has been a long and difficult struggle, owing to its intangibility. Yet even inelastic dark matter models present specialized obstacles. They are able to produce dark matter in abundance via processes such as thermal freeze-out, however, they hinder direct detection studies.
“It’s worth noting that models such as ours, with inelastic DM, are interesting because in addition to explaining the efficient generation of DM through the freeze-out mechanism, they also make it possible to circumvent the current limits of direct and indirect detection, as well as the limits of cosmology.” – Ana Luisa Foguel et al
Researchers are encountering major roadblocks in indirect detection ways. This poses a significant challenge, since there is no χ₂ that we can currently observe to decay into or annihilate with χ₁. This conversion from χ₁ to χ₂ is what makes direct detection possible. Alas, this process is still very difficult because χ₂ has a greater mass.
“And there’s also no χ₂ in the current universe to decay or annihilate with χ₁, producing signals that enable indirect detection. Furthermore, for χ₁ to interact in direct detection experiments, it’d have to transform into χ₂, which is very difficult because χ₂ is more massive,” – Foguel
As researchers seek to determine the properties of dark matter, knowing how it’s produced and the likelihood it interacts is essential.
