Which is the difference between gauge invariance and BRST invariance? Is it the same symmetry? Is the BRST the extention of the gauge symmetry even on the ghost fields?
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Yes, the BRST symmetry encodes the gauge symmetry. Briefly speaking, the gauge parameter in the infinitesimal gauge transformation is replaced with a ghost field of opposite Grassmann parity in the BRST transformation.
Yes, the gauge transformations are usually only defined for original gauge fields, while the BRST transformations are defined also for auxiliary fields.
answered Feb 14, 2023 at 10:14