A team of physicists from the University of Sao Paulo (USP) in Brazil has introduced a new theoretical framework that could advance the search for dark matter by focusing on inelastic particles that interact with ordinary matter through a novel type of force carrier. Their study, published in the Journal of High Energy Physics, proposes a model involving a massive vector boson that enables inter by Clarence Oxford
Los Angeles CA (SPX) Aug 01, 2025
A team of physicists from the University of Sao Paulo (USP) in Brazil has introduced a new theoretical framework that could advance the search for dark matter by focusing on inelastic particles that interact with ordinary matter through a novel type of force carrier. Their study, published in the Journal of High Energy Physics, proposes a model involving a massive vector boson that enables interaction between dark and visible matter.
"Dark matter constitutes roughly 27% of the universe, yet we still do not know its exact composition," said Ana Luisa Foguel, a Ph.D. student at USP's Physics Institute and lead author of the study. "In this work, we consider a dark sector containing light particles that interact weakly with known particles from the Standard Model."
For decades, dark matter candidates were presumed to be massive particles too heavy to produce in existing particle colliders. However, experiments like those at CERN's Large Hadron Collider have failed to detect such particles. This has driven researchers to explore lighter particles that interact very weakly-requiring experiments focused on ultra-sensitive detection of rare interactions.
Foguel and colleagues align their study with the "thermal freeze-out" mechanism, a well-known theory in cosmology where particles, once in thermal equilibrium with ordinary matter in the early universe, decouple as the universe expands and cools. After this decoupling, their abundance remains essentially fixed.
The model introduces a new particle, dubbed ZQ, which acts as a mediator between dark matter and Standard Model particles. Unlike the known W and Z bosons, ZQ is both massive and capable of directly coupling with standard particles. It facilitates interactions between two types of dark particles: a stable one (?1), which forms the bulk of dark matter, and a heavier, unstable partner (?2). These particles interact with ZQ simultaneously, defining the inelastic nature of the dark matter.
Importantly, the decay properties of ?2 help the model evade existing experimental constraints. During the cosmic recombination epoch, when energy injections into the primordial plasma would be noticeable in the cosmic background radiation, ?2's short lifetime ensures minimal impact. In the present-day universe, its absence reduces the likelihood of indirect detection signals. Direct detection is also hindered because converting ?1 into the heavier ?2 requires considerable energy.
"The inelastic nature of the particles allows our model to avoid current bounds from cosmology and dark matter searches," Foguel explained. "Furthermore, our mediator interacts directly with Standard Model particles, unlike the so-called 'vanilla' models that have largely been excluded by experimental data."
Foguel emphasized that the study not only proposes a viable mechanism for dark matter production through freeze-out but also makes a significant contribution to theoretical physics. The team developed and published computational tools to explore this model across a wide range of parameters. Their analysis identifies regions of the parameter space that are consistent with known dark matter abundance and are still untested by current experiments.
"Some of these unexplored regions could be probed in the next generation of particle physics experiments," Foguel said, highlighting the model's potential to guide future empirical investigations.
Research Report:Unlocking the inelastic Dark Matter window with vector mediators
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