# Tagged Questions

A fully relativistic (Lorentz covariant) description, first put forward by Paul Dirac in 1928, of the first quantized, spin one half fermion with nonzero mass. Physical notions to do with this equation include the Dirac sea, Dirac hole theory, the Klein Paradox and the fine structure of the Hydrogen ...

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### Is it true that the Schrödinger equation only applies to spin-1/2 particles?

I recently came across a claim that the Schrödinger equation only describes spin-1/2 particles. Is this true? I realize that the question may be ill-posed as some would consider the general ...
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### Time reversal operator symmetry of dirac lagrangian

I want to prove time reversal symmetry of Dirac Lagrangian, I have some problems with calculations. I start with \begin{eqnarray} T\psi T = U \psi \end{eqnarray} \begin{eqnarray} T\bar{\psi } T = ...
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### parity invariance of Einstein, Maxwell and Dirac Lagrangians

How can we show that Einstein, Maxwell and Dirac Lagrangians are parity invariant?
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### Kinetic energy operator in Dirac's relativistic quantum theory

In non-relativistic quantum theory $\hat{K}=\hat{p}^2/2m$, What is the Kinetic energy operator in Dirac's relativistic quantum theory?
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### Angular momentum operator for 2 dimensions?

Recently I get the task to build (2 + 1)-Dirac theory. I wrote corresponding Dirac equation in a form $$(i\sigma_{0}\partial_{0} + i\sigma_{1}\partial_{1} + i\sigma_{2}\partial_{2} - m)\Psi = 0,$$ ...
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### Relation between Dirac spinor and its adjoint

I'm trying unsuccessfully to solve the following problem in Thomson's Modern Particle Physics: "Starting from $(\gamma^{\mu} p_{\mu} - m) u =0,$ show that the corresponding equation for the ...
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I'd like to know if the sign in front of a kinetic term in QFT important. For the scalar field we conventionally write (in the $+ ---$ metric), {\cal L} _{ kin} = \frac{1}{2} \...
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### From Dirac to Klein-Gordon in curved spacetime

Is there an easy/elegant way of showing that "squaring" the Dirac equation in curved spacetime yields the Klein-Gordon equation, just like it happens in Minkowski space? A brute force approach would ...
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### Parity violating Dirac particle

We normally write down the Dirac Lagrangian as $${\cal L} _D = \bar{\psi} ( i \partial _\mu \gamma ^\mu - m ) \psi$$ but are the Lagrangian's, \bar{\...
I just started to learn how to quantise Dirac field. Meanwhile, as we can write the Dirac equation in terms of gamma matrices : $$(i\hbar\gamma^\mu\partial_\mu - m)\psi = 0$$ where $\gamma_\mu$ ...