A DM candidate indicated at Fermi-LAT and LZ ? Connection with LHC and LC prospects

For decades, physicists have chased a ghost that makes up most of the universe's matter but refuses to reveal itself. This invisible substance, known as dark matter, does not emit light, nor does it interact with the ordinary atoms that build our world, yet its gravity holds galaxies together. To find it, scientists look in two main ways: they wait for dark matter particles to bump into detectors deep underground, or they search for the faint glow of high-energy light produced when these particles collide and destroy each other in space. The question driving the latest research is simple yet profound: if we finally find a candidate for this missing mass, what kind of particle is it, and how does it behave?

A new analysis brings together two seemingly unrelated discoveries to propose a bold answer. Researchers at the Fermi-LAT space telescope have spotted an unexpected surplus of energetic photons, or light particles, centered around 20 GeV in the halo of our galaxy. At the same time, the LUX-ZEPLIN detector, a massive tank of liquid xenon buried deep underground, has recorded a single event that looks like a dark matter particle hitting a xenon atom. This event is significant because the energy deposited is so large that it is almost impossible to mistake for background noise. When combined, these two signals point toward a dark matter particle with a mass of a few hundred GeV. However, a puzzle remains: if this particle exists, why do we not see the same signal in dwarf galaxies, which are rich in dark matter but lack the signal seen in our own galaxy?

The authors of this study suggest that the solution lies in the speed of the particles and the nature of the force they use to interact. In our galaxy, dark matter particles move much faster than they do in the quiet, slow-moving dwarf galaxies. The researchers propose that these particles do not collide directly but instead interact through a heavy, short-lived particle with a spin of two, known as a Kaluza-Klein graviton. This specific type of interaction depends heavily on speed; because the particles in dwarf galaxies move so slowly, the chance of them colliding and producing light drops dramatically, explaining why those distant galaxies appear silent. This mechanism stands in stark contrast to older theories that suggested dark matter was a type of particle called a Higgsino, which would interact differently and predict a much heavier mass that does not fit the current data.

Support for this idea comes from the Large Hadron Collider, where scientists have been searching for signs of extra dimensions. The data from these collisions hints at a "tower" of these heavy graviton particles, with masses appearing at specific intervals, such as around 380 GeV, 700 GeV, and 1 TeV. One of these resonances could be the very particle that allows dark matter to annihilate in our galaxy. If this interpretation is correct, it changes the rules of the game. It suggests that the dark matter we are looking for is not the heavy Higgsino often predicted by standard theories, but rather a lighter particle, perhaps around 190 GeV, that couples to these graviton resonances.

The implications for future experiments are substantial. If these graviton resonances exist and interact with electrons, a future electron-positron collider could act as a factory to produce them in abundance. The researchers calculate that such a machine could generate thousands of these particles, allowing scientists to study their properties in detail and confirm whether they are indeed the key to dark matter. While the current evidence is still building, with the Fermi-LAT data showing a slight bump in the photon spectrum and the LHC seeing hints of these resonances, the convergence of signals from space, underground, and particle colliders offers a coherent picture. If confirmed, this would not only identify the dark matter particle but also provide the first concrete evidence for extra dimensions and a new layer of reality underlying our universe.