I was reading the book *Supersymmetry, Theory, Experiment and Cosmology* by P. Binétruy, and on page 25 the author goes from

$$ 1)[Q_r,Q_t]_+ \gamma^{0}_{ts}=2\gamma^{\mu}_{rs}P_{\mu} $$ $$ 2)\mbox{Contracting with $ \gamma^{0}_{sr}$, } \sum_{r,t}[Q_r,Q_r]_{+}(\gamma^{02})_{tr} = 2Tr(\gamma^{0}\gamma^{\mu})P_{\mu} $$
$$ 3) \sum_{r}Q^{2}_{r}=4P^{0}$$
$$ 4) H=\frac{1}{4}\sum_{r}Q^{2}_{r} $$

I don't really understand how to go from stage 1 to 2 or 3 to 4, can anyone help?

This post imported from StackExchange Physics at 2014-04-15 16:43 (UCT), posted by SE-user user21119