Quantum chromodynamics
Quarks, gluons, hadrons and the collective behavior of strongly interacting matter.
7 problemsParticle physics
Fundamental particles, interactions, and symmetries.
Explore Particle physics
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Browse collectionsMillennium Prize Problems
Five open problems from Clay’s famous prize program, linking mathematics with computation and mathematical physics.
5 problemsQuantum foundations
Measurement, gravity, and black holes challenge our account of quantum physics.
10 problemsQuarks and nuclear matter
Hadronic structure, magnetic-moment inputs and collective behavior in particle collisions.
7 problemsA few problems to explore
21 totalDark matter
Bent light and galaxy motions reveal gravity that known stars and gas cannot fully explain. What supplies the additional mass?
Quantum gravity
Gravity describes a changing spacetime. Quantum physics describes matter and its possibilities. How should they work together in a single physical account?
Matter–antimatter asymmetry
Matter and antimatter can annihilate each other. Yet the observable universe contains enough leftover matter to make stars, planets, and people. What produced that imbalance?
Strong CP problem
The theory of the strong nuclear force permits a kind of asymmetry that experiments find to be extraordinarily small. Why is nature so close to the symmetric case?
Yang–Mills existence and mass gap
A successful framework for particle physics still needs a rigorous four-dimensional construction with a positive gap above its vacuum energy.
Hierarchy problem
The Higgs field sets an important scale in particle physics. Why is that scale so much smaller than other scales that may enter the underlying theory?