Calculating the Transpose of Adjoint of Dirac Spinor

In summary, the question is about computing the transpose of the adjoint of a Dirac spinor. The conversation discusses two different ways of computing this, one based on Griffiths notation and the other based on Scadron's notation. Ultimately, it is concluded that the correct answer is {\bar u^T} = {\gamma _0}^T{u^*}, which is consistent with both notations.
  • #1
bjnartowt
284
3

Homework Statement



I want to compute the transpose of the adjoint of a Dirac spinor.

Homework Equations



My reasoning, based on learning Griffiths notation in “Intro to Elementary Particles”, p. 236, [7.58]:

[tex]{\bar u^T} = {({u^\dag }{\gamma _0})^T} = {\gamma _0}^T{u^\dag }^T<mathop> = \limits^{?} {\gamma _0}^T{u^*}[/tex]

But this contradicts what is written in Scadron (p. 100, [6.22], but using Griffiths definition of the adjoint, in contrast to Scadron’s p. 69, [5.29]): the transpose of the adjoint of a spinor is computed as:

[tex]\begin{array}{c}
{{\bar u}^T} = {\left( {\overline {\frac{{{p_\mu }{\gamma ^\mu } + m}}{{\sqrt {E + m} }}\left[ {\begin{array}{*{20}{c}}
{{\phi ^{(\lambda )}}({\bf{\hat p}})} \\
{\bf{0}} \\
\end{array}} \right]} } \right)^T} \\
= \frac{1}{{\sqrt {E + m} }}{\left( {\left[ {{{({p_\mu }{\gamma ^\mu })}^\dag }{\gamma _0} + m} \right]{{\left[ {\begin{array}{*{20}{c}}
{{\phi ^{(\lambda )}}({\bf{\hat p}})} \\
{\bf{0}} \\
\end{array}} \right]}^\dag }{\gamma _0}} \right)^T} \\
= \frac{1}{{\sqrt {E + m} }}{\gamma _0}{\left[ {\begin{array}{*{20}{c}}
{{\phi ^{(\lambda )}}({\bf{\hat p}})} \\
{\bf{0}} \\
\end{array}} \right]^*}\left[ {{\gamma _0}{{({p_\mu }{\gamma ^\mu })}^*} + m} \right] \\
{{\bar u}^T}<mathop> = \limits^{huh?} \frac{1}{{\sqrt {E + m} }}{\gamma _0}\left[ {{{({p_\mu }{\gamma ^\mu })}^T} + m} \right]{\left[ {\begin{array}{*{20}{c}}
{{\phi ^{(\lambda )}}({\bf{\hat p}})} \\
{\bf{0}} \\
\end{array}} \right]^*} \\
\end{array}[/tex]

As you can see: the
[tex]\sqrt {E + m} [/tex]

is trivial.
 
Last edited:
Physics news on Phys.org
  • #2
The Attempt at a SolutionI think the answer is:{\bar u^T} = {\gamma _0}^T{u^*}because this is consistent with Griffiths definition of the adjoint, and because it is also consistent with Scadron's equation (6.22).
 

What is the Dirac Spinor?

The Dirac Spinor is a mathematical object used in quantum field theory to describe the quantum state of a fermion, such as an electron or quark. It is a four-component complex vector that represents the spin and momentum of the particle.

What is the Adjoint of a Dirac Spinor?

The adjoint of a Dirac Spinor is the Hermitian conjugate of the spinor. This means that the complex conjugate of each component is taken and the order of the components is reversed. It is denoted by the symbol † and is used to construct the Dirac Lagrangian, which is an important equation in quantum field theory.

What is the Transpose of the Adjoint of a Dirac Spinor?

The transpose of the adjoint of a Dirac Spinor is obtained by swapping the rows and columns of the adjoint spinor. It is denoted by the symbol ‡ and is important in calculating the Dirac equation, which describes the behavior of fermions in a quantum field.

Why is Calculating the Transpose of the Adjoint of a Dirac Spinor Important?

Calculating the transpose of the adjoint of a Dirac Spinor is important because it allows us to manipulate and simplify mathematical expressions involving spinors. It is also necessary for solving the Dirac equation, which is a fundamental equation in quantum field theory.

How is the Transpose of the Adjoint of a Dirac Spinor Calculated?

To calculate the transpose of the adjoint of a Dirac Spinor, we first take the Hermitian conjugate of the spinor, then swap the rows and columns of the resulting matrix. This can be done using matrix algebra or by using the properties of complex conjugation and matrix transposition.

Similar threads

  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
3K
  • Advanced Physics Homework Help
Replies
0
Views
657
  • Advanced Physics Homework Help
Replies
5
Views
4K
Replies
2
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
1K
  • Differential Geometry
Replies
1
Views
1K
  • Advanced Physics Homework Help
Replies
2
Views
3K
  • Advanced Physics Homework Help
Replies
1
Views
2K
  • Advanced Physics Homework Help
Replies
1
Views
2K
Back
Top