Video winner of the 2025 Annual Review of Nuclear and Particle Science Video Contest

By Hernan E. Noriega and Bernardita Ried Guachalla.

This video explores one of the most intriguing questions in modern physics: the total neutrino mass. Once thought massless, neutrinos are now known to have mass, but recent results from cosmology suggest limits so tight they even hint at “negative” values. We explain what neutrinos are, how oscillation and direct experiments like KATRIN measure their mass, and why cosmology offers a powerful but indirect probe. Current results from DESI, Planck, ACT, and SPT push constraints to unprecedented levels, exposing tensions between particle physics and cosmology. Could this mean neutrinos hold the key to new physics, or even a revision of the ΛCDM model?

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