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Titolo: Unstable particles and nonconserved currents: a generalization of the FermionLoop scheme
Autore: Passarino, G;
 Indirizzi:
 Univ Turin, Dipartimento Fis Teor, Turin, Italy Univ Turin Turin ItalyUniv Turin, Dipartimento Fis Teor, Turin, Italy Ist Nazl Fis Nucl, Sez Torino, I10125 Turin, Italy Ist Nazl Fis Nucl Turin Italy I10125 , Sez Torino, I10125 Turin, Italy
 Titolo Testata:
 NUCLEAR PHYSICS B
fascicolo: 12,
volume: 574,
anno: 2000,
pagine: 451  494
 SICI:
 05503213(20000515)574:12<451:UPANCA>2.0.ZU;2T
 Fonte:
 ISI
 Lingua:
 ENG
 Soggetto:
 SINGLEW PRODUCTION; MONTECARLO PROGRAM; E(+)E() COLLISIONS; 4FERMION PHYSICS; LEP; ANNIHILATION; COUPLINGS; ENERGIES; BOSONS;
 Tipo documento:
 Article
 Natura:
 Periodico
 Settore Disciplinare:
 Physical, Chemical & Earth Sciences
 Citazioni:
 30
 Recensione:
 Indirizzi per estratti:
 Indirizzo: Passarino, G Univ Turin, Dipartimento Fis Teor, Via P Giuria 1, Turin, Italy Univ Turin Via P Giuria 1 Turin Italy iuria 1, Turin, Italy



 Citazione:
 G. Passarino, "Unstable particles and nonconserved currents: a generalization of the FermionLoop scheme", NUCL PHYS B, 574(12), 2000, pp. 451494
Abstract
The incorporation of finitewidth effects in the theoretical predictions for treelevel processes e(+)e() > n fermions requires that gauge invariance must not: be violated. Among various schemes proposed in the literature, the most satisfactory, from the point of view of field theory is the socalled FermionLoop scheme. It consists in the resummation of the fermioniconeloop corrections to the vectorboson propagators and the inclusion of all remaining fermionic oneloop corrections, in particular those to the YangMills vertices, In the original formulation, the FermionLoop scheme requires that vector bosons couple to conserved currents, i.e. that the massesof all external fermions be neglected, There are several examples where fermion masses must be kept to obtain a reliable prediction. The most famous one is the socalled singleW production mechanism, the process e(+)e > e()<(nu)over bar>(e)f(1)(f) over bar(2) where the outgoing electron is collinear, within a small cone, with the incoming electron. Therefore, m(e) cannot be neglected. Furthermore, among the 20 Feynman diagrams that contribute (for e<(nu)over bar>(e)u (d) over bar final states, up to 56 for e(+)e()nu(e)<(nu)over bar>(e)) there are multiperipheral ones that require a nonvanishing mass also for the other fermions. A generalization of the FermionLoop scheme is introduced to account for external, nonconserved, currents. Dyson resummed transitions are introduced without neglecting the p(mu)p(nu)terms and including the contributions from the HiggsKibble ghosts in the 't HooftFeynman gauge. Running vector boson masses are introduced and their relation with the corresponding complex poles are investigated, It is shown that any Jmatrix element takes a very simple form when written in terms of these running masses. A special example of Ward identity, the U(1) Ward identity for singleW, is derived in a situation where all currents arenonconserved and where the top quark mass is not neglected inside loops. (C) 2000 Elsevier Science B.V. All rights reserved.
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Documento generato il 24/11/20 alle ore 22:21:52