Retrieving "Qcd Sum Rules" from the archives

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1. Quark Condensate

   Linked via "QCD sum rules"

   The relationship between the condensate and the vacuum energy density is complex and often tied to phenomenological models that incorporate aspects of Quantum Electrodynamics (QED)/) polarization. It is generally accepted that the non-zero condensate contributes a substantial, negative component to the vacuum energy density. While the precise calculation remains an outstanding challenge, early estimations based on the [Witten-Veneziano sum rules](/entries/…