The 4PI effective action for theory
Department of Physics, Brandon University, R7A 6A9, Brandon, Manitoba, Canada
2 Winnipeg Institute for Theoretical Physics, Winnipeg, Manitoba, Canada
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Published online: 26 May 2004
We work with theory and study the 4PI effective action at 3-loop order. We discuss the relation between the equations of motion obtained by taking functional derivatives of the effective action with respect to the variational parameters, and the Schwinger-Dyson (SD) equations. We show that the equation obtained by differentiating with respect to the connected 2-point function is identical to the SD equation for the truncated 2-point function; differentiating with respect to the connected 3-point function reproduces the SD equation for the truncated 3-point function, up to 1-loop order; and differentiating with respect to the connected 4-point function reproduces the SD equation for the truncated 4-point function, at the tree level. These results establish a connection between two techniques for performing non-equilibrium calculations, and provide a starting place for a study of the gauge dependence of quantities derived from an nPI effective action.
© Springer-Verlag, 2004