Spin – for state at rest

1. Spin – for state at rest Since we have a (two-fold) degeneracy there must be some operator which commutes with the energy operator and whose eigenvalues label the two states

2. Spin – for state NOT at rest Helicity Eigenvalues (More generally, in arbitrary frame, spin given by boosting result at rest -

3. Inclusion of electromagnetic interaction

4. Nonrelativistic limit Dominant time dependence large component small component

5. Gyromagnetic ratio =2 predicted

6. Spin – for state at rest Since we have a (two-fold) degeneracy there must be some operator which commutes with the energy operator and whose eigenvalues label the two states

7. Spin – for state NOT at rest Helicity Eigenvalues (More generally, in arbitrary frame, spin given by boosting result at rest -

8. Zero mass fermions – the two component neutrino Weyl basis For m=0 …no mixing Both have +ve and –ve energy solution Negative helicity neutrino - LH Positive helicity antineutrino - RH Projects LH neutrino

9. Parity Parity invariant (neutrinos violate parity)