#### Wrichik Basu

Gold Member

2018 Award

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The authors write at the beginning of the book that ##p## means a 4-vector,

**means a 3-vector, and ##\mathbf{p}## means the magnitude of the 3-vector.**

*p*With this in place, for the Fourier decomposition of the Dirac field, the authors write:

Here, the integration variable is ##p## (the four-vector), the arguments of the creation and annihilation operators for the particle and antiparticle (##f_s## and ##\hat{f_s ^\dagger}##) and the spinors (##u_s## and ##v_s##) is

**, the 3-vector.**

*p*In the expression in the exponent, is it the 4-vectors or the 3-vectors that are being dotted?

A similar problem occurs for photon fields:

Again, is the argument in the exponent the 4-vectors or 3-vectors?

Unfortunately, at this moment I can no longer access the print book. It will be very helpful if someone clarifies the notation.