I just started learning this so I am a bit lost. This is where I am lost http://www.nyu.edu/classes/tuckerman/quant.mech/lectures/lecture_7/node1.html .(adsbygoogle = window.adsbygoogle || []).push({});

Why when E>0, we use $$\phi_p=

\begin{pmatrix}

1 \\

0 \\

\end{pmatrix}

$$ or $$

\begin{pmatrix}

0 \\

1 \\

\end{pmatrix}

$$

while when E<0, we use this instead

$$x_p=

\begin{pmatrix}

1 \\

0 \\

\end{pmatrix}

$$ or $$

\begin{pmatrix}

0 \\

1 \\

\end{pmatrix}

$$

where ∅_{p}is the upper component while x_{p}is the lower component of the bispinor in Dirac equation.

Can we do it the other way round or

$$\phi_p=

\begin{pmatrix}

1 \\

0 \\

0 \\

0 \\

\end{pmatrix}

....$$ instead?

Secondly, how did the author convert $$\phi_p = \frac{c \sigma .p}{E_p -mc^2}x_p=?=\frac{-c \sigma .p}{|E_p| +mc^2}x_p$$? Does the mod sign means anything?

Can someone help me or point me in the right direction cause this is my first time learning this. Thanks a lot!

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# I Need help with Dirac Equation

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