Rare charged particle could redefine dark matter

Dark matter sits in the background of the universe, shaping galaxies while refusing to reveal itself. Many searches have chased neutral particles and come up empty.

A different idea is now on the table: a particle called the gravitino, which is super heavy, stable, and slightly electric. It would be rare, so it would not light up the sky – yet it could leave a subtle trace in the right kind of detector.

Krzysztof A. Meissner of the Faculty of Physics at the University of Warsaw (FUW) is one of the experts developing this idea and the strategy to look for it.

The loophole in dark matter rules

Charged dark matter sounds ruled out, but the strongest constraints target lighter, more common particles that would have left clear signals in cosmology or in the Milky Way’s disk.

If each particle instead carries enormous mass near the Planck scale and is extremely scarce, the population can be so thin that it avoids those limits while still accounting for the Milky Way’s typical dark matter density.

The catch is detection. A particle this rare might pass through a detector only occasionally, and it would move slowly by particle-physics standards.

That slow speed is useful: it stretches the flash of light from the particle’s passage into a long, faint glow that electronics can separate from ordinary, brief events.

The search for dark matter

JUNO is a spherical detector about 116 feet (35 meters) across, holding roughly 22,000 tons of organic scintillator and ringed by nearly 17,600 large light sensors to catch tiny bursts of photons.

Those sensors are photomultiplier tubes. They are tuned to detect neutrino events, but their sensitivity and coverage also make them well suited to catching dim, stretched signals that last much longer than a standard neutrino flash.

Across the ocean, DUNE will use a vast pool of liquid argon with imaging readout, plus its own photon-detection system. That combination can register a slow, straight track if the particle sheds energy into electronic excitations along its path.

Both experiments were built for neutrinos, yet their scale, timing precision, and light collection happen to fit the needs of this search.

A unique charged particle signature

A peer-reviewed analysis shows that a passing charged gravitino would gently excite molecules in JUNO’s liquid. Those molecules would re-emit light over a span ranging from a few microseconds up to a few hundred microseconds, depending on speed and geometry.

The researchers describe the resulting pattern as a “unique and unmistakable signature,” said Meissner.

The predicted track is quiet, linear, and extended in time. It would not resemble the sharp nanosecond flashes created by ordinary neutrino interactions.

The same calculation indicates that liquid argon in DUNE should also glow enough for detection. The shapes differ, but the long timing window remains the key feature.

The math behind the particles

The charged gravitino concept grows from supergravity, a framework that ties gravity to the quantum fields of matter. A recent proposal aligns the known quarks and leptons with a highly symmetric theory and predicts eight supermassive gravitinos with fractional charge.

Two of those states carry charge two-thirds of the electron’s charge. They cannot decay into ordinary matter because no allowed final state matches their quantum numbers.

That makes them stable on cosmic timescales. It also suggests a different kind of search signal than the neutral candidates pursued for decades.

This pathway pulls mathematics, particle physics, and detector engineering into the same room. It also borrows tools from quantum chemistry to compute how a slow, heavy particle tickles molecules in a liquid.

What this would mean for physics

Seeing one event with the predicted time profile would not be enough on its own. The track must be reconstructed across many sensors, and backgrounds must be tested against the same criteria.

Repeated detection would seal the case. A series of steady, linear glows lasting microseconds would signal a new particle instead of mere instrument noise.

A detection would carry a message from extreme energies. It would hint that gravity and quantum fields meet in a way that leaves fingerprints inside large underground tanks filled with carefully prepared liquid.

Such a discovery would also reshape how we think about dark matter. The field would shift from chasing neutral particles toward a search that embraces rare charge and enormous mass.

A null result would still be valuable. JUNO and DUNE can set limits on how faint, how slow, and how infrequent such particles may be without appearing.

The study is published in the journal Physical Review Research.

Image Credit: NASA, ESA, and the Hubble Heritage Team

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