• Dark matter
• Not protons, neutrons, or others
○ Too few
• Not: neutrino
○ Once a possibility
○ But: too lightweight
○ Hot
§ Move: as the light
• Best fit: cold dark matter
○ Move sluggishly
○ Minor problems
○ Plausible candidates
§ Supersymmetry: superpartner
□ Heavier
□ Several natural candidates
® Neutralino
◊ Amalgam: photon, boson and others
◊ Name: sounds like"nertrino"
◊ Lightest + stable
◊ Zero charge
® Satisfy the requirements of cold dark matter
1. Topic: what's the material of dark matter. Theory: it can't be … example to support this theory
2. Another exception is neutrinos, which unattached to any atom. The experiments have found out N is too light and too hot to be the matter of dark matter.
3. Pointing out an possibility:“ cold” dark matter. Even though cold dark matter faces some minor problem, but compared with others, it's much easier and reasonable.
4. The most studied extension is supersymmetry. The new particles are all heavier. List down several natural candidates.
N is the lightest one in the supersymmetry and stable. And it has zero charge. Hence it satisfies all the requirements of cold dark matter.