1. We follow the interpretation and notation given in a recent paper:Ann. of Phys.,71, 519 (1972).
2. Equation (2) without the «mass» term was first written down byY. Murai:Progr. Theor. Phys. (Kyoto),18, 109 (1955).
3. One possible representation ofβ a isβ u =γ u ·⋌σ3,β 4 =γ 5 ·⋌σ3,β 6 =1·⋌σ1,which givesβ ϰ.
4. It is assumed thatp λ≠0 in the rest framep 1=p 2=p 3=0. Hence we must do a «tilt» to get rid of theΣ ϰλ term. In this space, since β0 is diagonal, the parity operatorP=β 0 β 4 β 6 is proportional to $$P \equiv \beta ^0 \beta ^4 \beta ^6 = \left\{ {_{\gamma ^0 \gamma ^5 0}^{0 \gamma ^0 \gamma ^5 } } \right\}$$ .
5. The positive definite scalar product for the 8-component equation is Lorentz invariant, but not conformally invariant. This is so because the little group we are using isSO 4,3 and unitary representations are infinite dimensional; therefore the μ states are unstable. The nonunitarity means that the decay products are not included in the description.