Standard Model of Particle Physics
Quarks, leptons, gauge bosons, and the Higgs — the field content of the Standard Model.
The Standard Model (SM) is a relativistic quantum field theory with gauge group
$$SU(3)_C \times SU(2)_L \times U(1)_Y.$$Matter: three generations of quarks $(u,d), (c,s), (t,b)$ and leptons $(\nu_e, e), (\nu_\mu, \mu), (\nu_\tau, \tau)$. Each fermion is a left-handed weak doublet and a right-handed weak singlet — chirality is fundamental.
Forces are mediated by gauge bosons:
- Strong: 8 gluons of $SU(3)_C$, coupling color charge. Confines quarks into hadrons.
- Electroweak: 4 gauge bosons mix into the massless photon $\gamma$ + massive $W^\pm$ ($\approx 80$ GeV) and $Z$ ($\approx 91$ GeV) after Higgs breaking.
- Higgs boson ($H$, 125 GeV, discovered 2012 at LHC): gives mass to $W, Z$ and the charged fermions via Yukawa couplings.
Tested to extraordinary precision. Known incompleteness: doesn't include gravity, doesn't explain dark matter, neutrino masses fit by adding tiny extra terms, hierarchy problem ($M_H \ll M_{Pl}$), strong CP problem, baryon asymmetry, etc.
Interactive: the SM particle table
Click a particle to highlight which forces it feels.
Click a particle.