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In QED, the photon field has the following commutation relations: \begin{equation} [A^{\mu}(t,\vec{x}),A^{\nu}(t,\vec{y})]=0, \tag{1} \end{equation} where $A^{\mu}(t,\vec{x})$ is the photon filed. As for QCD, I can not find similar relations for gluon, can we have \begin{equation} [A_a^{\mu}(t,\vec{x}),A_a^{\nu}(t,\vec{y})]=0 \, \, \, \, \, (2) \end{equation} for gluon field with color index $a$? Or do we have the following equation \begin{equation} [A_a^{\mu}(t,\vec{x}),A_a^{\nu}(t,\vec{x})]=0 \, \, \, \, \, (3) \end{equation} for gluon at same $x$? From the definition of gluon field-strength tensor \begin{equation} F^{\mu \nu}=\partial^{\mu}A^{\nu}-\partial^{\nu}A^{\mu}-ig[A^{\mu},A^{\nu}], \, \, \, \, \, (4) \end{equation} where $A^{\mu}=A_a^{\mu}t^a$, the last term of Eq.(4) is often reexpressed as \begin{equation} [A^{\mu},A^{\nu}]=A_a^{\mu}A_b^{\nu}t^a t^b-A_b^{\nu}A_a^{\mu}t^bt^a=A_a^{\mu}A_b^{\nu} [t^a, t^b].\, \, \, \, \, (5) \end{equation} Does Eq.(5) implies that \begin{equation} A_a^{\mu}A_b^{\nu}=A_b^{\nu}A_a^{\mu} \, \, \, \, \, (6) \end{equation} thus gluon commutes at the same position. Could someone tell me which of the above equations are not correct, or how do we understand the commutation relations of gluon?

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    $\begingroup$ It would be nice if you referenced (1); the ET commutator vanishes because the structure of coefficients of the constituent oscillators lacks the "interesting snag" of canonically conjugate fields. (Practice with scalar QFT first, abelian and non-abelian). The interesting pieces, however, are the ones involving fields and field momenta, which contain the singularities... Do you want an answer for scalar fields, eschewing the irrelevant complexities? $\endgroup$ Commented Jun 26 at 14:35
  • $\begingroup$ Thanks very much, Eq.(1) is from Eq.(6.93b) of the book "Field quantization, greiner", what am I interested is the hadronic matrix element of the vector field $A^{\mu} A^{\nu}$, I guess that singularities do not contribute? $\endgroup$ Commented Jun 26 at 14:45
  • $\begingroup$ I don't have his book, but, indeed, there are no equal time singularities, for the analogous reason there are no φφ ones... The singularities emerge for combinations of a field with its canonical conjugate... $\endgroup$ Commented Jun 26 at 15:00
  • $\begingroup$ Since, the fields decouple for different colors, the analog of (1) is (2), where the color indices a are not summed over. Again, singularities only emerge for canonical momentum involvement, the analog of (6.93a). With the suitable equal time indices inserted, (6) comports with (2). $\endgroup$ Commented Jun 27 at 14:36
  • $\begingroup$ Thanks very much for your comment, Eq. (6) is equal time commutation, and I also find two papers on the gluon commutation relations, they are: doi.org/10.1103/PhysRevD.1.2901; doi.org/10.1103/PhysRevD.8.2736. I am studing those papers now, and it seems that the commutation relations are complicated for gluons. $\endgroup$ Commented Jun 27 at 17:17

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