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I'm tring to check some calculations of the propagator of a gauge field using the [itex]R_\xi[/itex] gauge fixing.

Since the propagator has a matricial structure,

[itex]\Delta_{\mu\nu}=\frac{1}{(p^0)^2+E_p^2}\left[\delta_{\mu\nu}-\frac{1-\xi}{(p^0)^2+E_p^2}p_\mu p_\nu\right], [/itex]

I'd like to check it using that fact. Using the command line

Array[(KroneckerDelta[#1,#2]-(1- xi) p[#1] p[#2]/(p[0]^2+ep^2))/(p[0]^2+ep^2) & , {4,4}, {0,0}]

I was able to write the needed expression, but then I'd like to compute the residues of ANY component... without losing the matricial structure. Is this possible?

All my guesses are fraud.For example.... if I try to give a name to the array

M=Array[(...)]

it does not recognize the matrix structure.

Whatever help is useful. Thanks.

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# How do I use tensors in Mathematica 7?

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