English

Ghosts that Connect

History and Philosophy of Physics 2026-07-29 v1 High Energy Physics - Theory

Abstract

The Faddeev--Popov procedure poses two conceptual puzzles. \emph{Puzzle~(1)}: if gauge-equivalent configurations represent the same physics, the quotient \F/\G\F/\G should suffice to compute physical amplitudes --- yet the procedure requires anti-commuting auxiliary fields, the ghosts, with no analogue on the quotient. What structure of \F\F do they encode? \emph{Puzzle~(2)}: gauge-fixing was supposed to eliminate local gauge symmetry, yet the gauge-fixed theory retains BRST --- a residual symmetry that acts on the gauge potential as an infinitesimal gauge transformation. Why does it survive? Both puzzles dissolve together. Following \textcite{Dougherty2021} and \textcite{DoughertyRead2026}, I take ghosts to encode classical content of \F\F/\G\F \to \F/\G, but identify a different structure: a principal connection ϖ\varpi on this bundle. The ghost is ϖ\varpi; the BRST operator is the vertical exterior derivative on field space; the Maurer--Cartan equation is its vertical Cartan structure equation. The Faddeev--Popov calculus draws only on ϖ\varpi's vertical content, which the algebraic reading also captures; ϖ\varpi's horizontal content, on which the Vilkovisky--DeWitt programme rests, supplies the cross-orbit pairing that gauge-fixing, dressing-based quantisation, and counterfactual comparison require and the quotient discards. BRST is the rigid, vertical symmetry that preserves this pairing; this is why it survives gauge-fixing.

Cite

@article{arxiv.2607.27297,
  title  = {Ghosts that Connect},
  author = {Henrique Gomes},
  journal= {arXiv preprint arXiv:2607.27297},
  year   = {2026}
}