weak interactions

• one of the four fundamental interactions, the only one that changes quark or lepton flavour (e.g. d → u)
• carriers: W⁺ and W⁻ (80.4 GeV/c²) and Z⁰ (91.2 GeV/c²) bosons
• very short range (~10⁻¹⁸ m), because the carriers are heavy
• β decay: inside a neutron, d → u + e⁻ + ν̄ₑ
• first step of the Sun’s fusion: p + p → ²H + e⁺ + νₑ
• violates parity (W bosons couple only to left-handed particles and right-handed antiparticles) and CP (first seen in kaon decays, 1964)
• unified with electromagnetism in the electroweak theory
• together with gravity, the only interactions neutrinos feel