Hermitian conjugate of plane wave spinors for Dirac equation

Next, we can use the Dirac equation to simplify this expression. We know that \gamma^{\mu}p_{\mu}u_{s}(p)=m\omega_{p}u_{s}(p), so we can rewrite our expression as: u^{+}_{r}(p)u_{s}(p)=\
  • #1
bubblehead
6
0
I need to show that

[itex]u^{+}_{r}(p)u_{s}(p)=\frac{\omega_{p}}{m}\delta_{rs}[/itex]

where
[itex]\omega_{p}=\sqrt{\vec{p}^2+m^{2}}[/itex]
[itex]u_{r}(p)=\frac{\gamma^{\mu}p_{\mu}+m}{\sqrt{2m(m+\omega_{p})}}u_{r}(m{,}\vec{0})[\itex] is the plane-wave spinor for the positive-energy solution of the Dirac equation.

I think my problem is twofold: I'm not sure I've computed the Hermitian conjugate of the spinor correctly (just the gamma matrix and p have Hermitian conjugates, is that right?) and I'm not sure how/why the normalization term disappears when squared. Either way, I'm not getting the nice simple answer I should!
 
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  • #2
So any help would be much appreciated. The Hermitian conjugate of the spinor is given by u^{+}_{r}(p)=\frac{\gamma^{\mu}p_{\mu}+m}{\sqrt{2m(m+\omega_{p})}}u^{+}_{r}(m{,}\vec{0})Using this, we can compute u^{+}_{r}(p)u_{s}(p):u^{+}_{r}(p)u_{s}(p)=\frac{\gamma^{\mu}p_{\mu}+m}{\sqrt{2m(m+\omega_{p})}}u^{+}_{r}(m{,}\vec{0}) \cdot \frac{\gamma^{\nu}p_{\nu}+m}{\sqrt{2m(m+\omega_{p})}}u_{s}(m{,}\vec{0}) =\frac{\gamma^{\mu}p_{\mu}+m}{\sqrt{2m(m+\omega_{p})}} \cdot \frac{\gamma^{\nu}p_{\nu}+m}{\sqrt{2m(m+\omega_{p})}} \cdot u^{+}_{r}(m{,}\vec{0})u_{s}(m{,}\vec{0})=\frac{(\gamma^{\mu}p_{\mu}+m)(\gamma^{\nu}p_{\nu}+m)}{2m(m+\omega_{p})} \cdot u^{+}_{r}(m{,}\vec{0})u_{s}(m{,}\vec{0})Now, note that (\gamma^{\mu}p_{\mu}+m)(\gamma^{\nu}p_{\nu}+m)=(p^2+m^2)+2m\gamma^{\mu}p_{\mu}Substituting this into our expression for u^{+}_{r}(p)u_{s
 

What is the Hermitian conjugate of a plane wave spinor?

The Hermitian conjugate of a plane wave spinor is the complex conjugate of the transpose of the spinor. It is denoted by a dagger symbol (†) and is used in the Dirac equation to represent the adjoint of the spinor.

Why is the Hermitian conjugate important in the Dirac equation?

The Hermitian conjugate is important in the Dirac equation because it allows us to define a conserved current, which is essential for understanding the behavior of particles in quantum mechanics. It also helps us define the probability density of finding a particle at a particular location and time.

How is the Hermitian conjugate related to spinors and the Dirac equation?

The Hermitian conjugate is related to spinors in the Dirac equation because it allows us to define the adjoint of a spinor, which is needed for the formulation of the Dirac equation. It also helps us define the inner product between two spinors, which is used in calculations involving spinors.

What is the difference between the Hermitian conjugate and the complex conjugate?

The Hermitian conjugate and the complex conjugate are related but not the same. The complex conjugate is the result of changing the sign of the imaginary part of a complex number, while the Hermitian conjugate also involves taking the transpose of a matrix. In the context of spinors, the Hermitian conjugate is used to define the adjoint of a spinor, while the complex conjugate is used to define the inner product between two spinors.

How is the Hermitian conjugate used in calculations involving spinors?

The Hermitian conjugate is used in calculations involving spinors to define the adjoint of a spinor, which is needed for the formulation of the Dirac equation. It is also used to define the inner product between two spinors, which is used in calculations of probabilities and conserved currents in quantum mechanics.

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