I heard in a conference that gravity forbids to construct local gauge invariants like [itex]Tr-\frac14 F^{\mu\nu}_aF_{\mu\nu}^a[/itex] and only allows non-local gauge invariant quantities like Wilson Loops: [itex]Tr P e^{\oint_{\gamma} A_a dx^a}[/itex]. Could someone explain me where does it come from? I have a basis knowledge of QFT and GR. If you could had a reference it would be great!(adsbygoogle = window.adsbygoogle || []).push({});

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# Why does gravity forbid local observables?

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