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Gauge-independent off-shell fermion self-energies at two loops: The cases of QED and QCD

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Gauge-independent off-shell fermion self-energies at two loops: The cases of QED and QCD

dc.contributor.author	Binosi, Daniele
dc.contributor.author	Papavassiliou, Joannis
dc.date.accessioned	2015-04-10T08:23:50Z
dc.date.available	2015-04-10T08:23:50Z
dc.date.issued	2002
dc.identifier.uri	http://hdl.handle.net/10550/43004
dc.description.abstract	We use the pinch technique formalism to construct the gauge-independent off-shell two-loop fermion self-energy, both for Abelian (QED) and non-Abelian (QCD) gauge theories. The new key observation is that all contributions originating from the longitudinal parts of gauge boson propagators, by virtue of the elementary tree-level Ward identities they trigger, give rise to effective vertices, which do not exist in the original Lagrangian; all such vertices cancel diagrammatically inside physical quantities, such as current correlation functions or S-matrix elements. We present two different, but complementary derivations: First, we explicitly track down the aforementioned cancellations inside two-loop diagrams, resorting to nothing more than basic algebraic manipulations. Second, we present an absorptive derivation, exploiting the unitarity of the S-matrix, and the Ward identities imposed on tree-level and one-loop physical amplitudes by gauge invariance, in the case of QED, or by the underlying Becchi-Rouet-Stora symmetry, in the case of QCD. The propagator-like sub-amplitude defined by means of this latter construction corresponds precisely to the imaginary parts of the effective self-energy obtained in the former case; the real part may be obtained from a (twice subtracted) dispersion relation. As in the one-loop case, the final two-loop fermion self-energy constructed using either method coincides with the conventional fermion self-energy computed in the Feynman gauge.
dc.language.iso	eng
dc.relation.ispartof	Physical Review D, 2002, vol. 66, num. 8, p. 085003
dc.source	Binosi, Daniele Papavassiliou, Joannis 2002 Gauge-independent off-shell fermion self-energies at two loops: The cases of QED and QCD Physical Review D 66 8 085003
dc.subject	Física
dc.title	Gauge-independent off-shell fermion self-energies at two loops: The cases of QED and QCD
dc.type	journal article	es_ES
dc.date.updated	2015-04-10T08:23:50Z
dc.identifier.doi	http://dx.doi.org/10.1103/PhysRevD.65.085003
dc.identifier.idgrec	091145
dc.rights.accessRights	open access	es_ES