Madrid, September 2025.– The Institute for Theoretical Physics (IFT UAM-CSIC) hosted the Light Dark World 2025 (LDW25) conference from September 16 to 19, bringing together around 70 researchers from across the globe to discuss the latest advances in the search for new particles beyond the Standard Model and in the study of dark matter.
Over four days, specialists from universities and research centers in Europe, the Americas, and Asia shared results and perspectives on one of the great mysteries of contemporary physics: the nature of dark matter, which makes up about 27% of the universe and whose composition remains unknown; as well as light and invisible particles, such as neutrinos, and other exotic particles.
Pilar Coloma, organizer of the event and researcher at the IFT, explained the aim of the conference: “We have focused on discussing extensions of new physics with particles somewhat different from the usual ones, always light particles. In addition, we have included the experimental approach to look for this kind of models.”
Laura Molina Bueno (IFIC-CSIC) referred specifically to the close collaboration between theorists and experimentalists, which is essential when doing physics: “Theorists suggest the most interesting parameter spaces to explain issues such as dark matter or why neutrinos have mass. There is also enormous variety within the experimental community, whose expertise allows us to use different experiments and obtain answers more quickly.”
Axions: exotic candidates for dark matter
One of the central topics of the conference was axions, hypothetical particles with extremely light mass and weak interaction, which could not only explain dark matter but also solve open problems of the Standard Model.
Researcher Javier Redondo (University of Zaragoza) highlighted: “Nature seems to be suggesting that, if we consider this particle, we can understand at the same time why we have never observed certain effects in neutrons and what dark matter is made of. It is fascinating to think that a single piece might fit into two different puzzles.”
Redondo also emphasized the importance of holding international meetings for scientific collaboration: “These conferences are the fundamental tool for exchanging ideas, confronting them, and generating collaborations that would otherwise be impossible. Modern science is built in networks.”
On the verge of solving the problem of neutrino masses?
Renata Zukanovich-Funchal, a researcher at the University of São Paulo with nearly 30 years of experience in neutrinos, explained that the major current issue is that we do not know the exact order of the masses of the three neutrinos. “We know that we have three neutrinos with different masses because we have observed oscillations… but we do not know whether the third neutrino is actually the heaviest or the lightest,” she noted. This question is known as the mass hierarchy problem: it can be “normal” (the third is the heaviest) or “inverted” (the third is the lightest).
To resolve this, Renata pointed to the Chinese JUNO (Jiangmen Underground Neutrino Observatory) experiment, the largest neutrino detector in the world, which studies neutrinos produced in nuclear reactors. According to her, “it is going to be extremely precise… they are going to measure effects we have never seen before,” and there is hope that “we will see it in 2026.” If confirmed, this result would finally clarify the mass structure of neutrinos, one of the most persistent enigmas in particle physics.
The researcher expressed optimism: “We are very close to solving a mystery we have been pursuing for decades. With the level of precision we are reaching, we could have answers before 2026.”
New horizons in detection
Major international direct detection experiments, such as LZ (USA) and PandaX (China), were at the center of the debate.
According to Kimberly Paladino (University of Oxford): “Although our detectors are optimized for heavy particles, we have discovered that they are also sensitive in lighter regions, which opens new search windows. This kind of meeting is fundamental because it brings theorists and experimentalists together: many times the next big idea is born from an informal conversation.”
The conference also featured the participation of many young predoctoral researchers. Pablo Blaco, from the IFT, highlighted the variety of topics presented in the talks: “It is always interesting to learn about the different areas within the dark sectors. I am looking forward to meeting people who work in this kind of physics.”
During the conference, a poster session was also held, where the most outstanding work was awarded. The winner was David Alonso, a predoctoral researcher at the IFT, who presented new signals of a type of exotic particle known as “axion-like particles”: “We are investigating a new type of signal that could be studied in neutrino experiments known as Cherenkov experiments. In our work we predict the possible production of this type of particle in supernovae and, since we have not yet detected them, we are able to set limits on the magnitude that measures the interaction of these new particles with the type of ordinary matter we all know.”
