Stable calculations for unstable particles: restoring gauge invariance

Argyres, E.N.; Beenakker, W.; Oldenborgh, Geert Jan van; Denner, Ansgar; Dittmaier, S.; Hoogland, Jiri; Kleiss, R.; Papadopoulos, Costas G.; Passarino, Giampiero

doi:10.1016/0370-2693(95)01002-8

Cited by 123 publications

(89 citation statements)

References 13 publications

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“…The following ratios give an illustration of the e ects of the nite width, the ISR, background diagrams and of non-standard couplings: R 1 = SM SM;on ; (17) R 2 = SM;ISR SM ; (18) R 3 = SM;all SM ; (19) R 4 = AN SM ; (20) R 5 = AN;all SM;all : (21) The reaction which we take as example is e e + ! e e u d: (22) The following input parameters are used …”

Section: Resultsmentioning

confidence: 99%

Anomalous four-fermion processes in electron-positron collisions

Berends

Sighem

1995

Nuclear Physics B

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This paper studies the electroweak production of all possible fourfermion states in e + e collisions with non-standard triple gauge boson couplings. All CP conserving couplings are considered. It is an extension of the methods and strategy, which were recently used for the Standard Model electroweak production of four-fermion nal states. Since the fermions are taken to be massless the matrix elements can be evaluated e ciently, but certain phase space cuts have to be imposed to avoid singularities. Experimental cuts are of a similar nature. With the help of the constructed event generator a number of illustrative results is obtained for W -pair production. These show on one hand the distortions of the Standard Model angular distributions caused by either o -shell e ects or initial state radiation. On the other hand, also the modi cations of distributions due to anomalous couplings are presented, considering either signal diagrams or all diagrams.

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Section: Resultsmentioning

confidence: 99%

Anomalous four-fermion processes in electron-positron collisions

Berends

Sighem

1995

Nuclear Physics B

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“…refs. [96][97][98][99][100][101]), the inclusion of NLO effects complicates things further. Currently, the most pragmatic and widely-used solution is the so-called complex mass scheme [102,103], that basically amounts to an analytic continuation in the complex plane of the parameters that enter the SM Lagrangian, and which are related to the masses of the unstable particles.…”

Section: Jhep07(2014)079mentioning

confidence: 99%

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

Alwall

Frederix

Frixione

et al. 2014

J. High Energ. Phys.

6,093

5,572

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We discuss the theoretical bases that underpin the automation of the computations of tree-level and next-to-leading order cross sections, of their matching to parton shower simulations, and of the merging of matched samples that differ by light-parton multiplicities. We present a computer program, MadGraph5 aMC@NLO, capable of handling all these computations -parton-level fixed order, shower-matched, merged -in a unified framework whose defining features are flexibility, high level of parallelisation, and human intervention limited to input physics quantities. We demonstrate the potential of the program by presenting selected phenomenological applications relevant to the LHC and to a 1-TeV e + e − collider. While next-to-leading order results are restricted to QCD corrections to SM processes in the first public version, we show that from the user viewpoint no changes have to be expected in the case of corrections due to any given renormalisable Lagrangian, and that the implementation of these are well under way.

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“…The schemes developed in [8][9][10][11] for the introduction of the finite width effects, while keeping electromagnetic gauge invariance, are based in two main observations: In quantum field theory the width is naturally included in the imaginary part of the self-energy of the particles and, the Ward identity is respected at all orders in perturbation theory. These facts are exploited in those schemes by including the resummation of the fermion/boson loops in the propagator and the corrections in the electromagnetic vertices.…”

Section: Finite Width Effectsmentioning

confidence: 99%

“…To do so, several schemes have been developed, we can mention, for example, the so called fermion loop scheme [8][9][10] and the boson loop scheme [11] (suitable for the W and ρ bosons respectively), which consider that Γ is naturally included in the calculations by taking into account the absortive contributions in the electromagnetic vertex and in the propagator. Under these schemes, the electromagnetic vertex V V γ is modified respect to the tree level form in a non-trivial way.…”

Section: Introductionmentioning

confidence: 99%

Finite width induced modification to the electromagnetic form factors of spin-1 particles

Gudiño

Sánchez

2010

Phys. Rev. D

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The inclusion of the unstable features of a spin-1 particle, without breaking the electromagnetic gauge invariance, can be properly accomplished by including higher order contributions as done in the so-called fermion loop scheme (for the W gauge boson), and the boson loop scheme (for vector mesons). This induces a non trivial modification to the electromagnetic vertex of the particle, which must be considered in addition to any other contribution computed as stable particles. Considering the modified electromagnetic vertex, we obtain general expressions for the corresponding corrections to the multipoles as a function of the mass of the particles in the loop. For the W gauge boson no substantial deviations from the stable case is observed. For the ρ and K * mesons the mass of the particles in the loop makes a significant effect, and can be comparable with corrections of different nature .

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Stable calculations for unstable particles: restoring gauge invariance

Cited by 123 publications

References 13 publications

Anomalous four-fermion processes in electron-positron collisions

Anomalous four-fermion processes in electron-positron collisions

The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations

Finite width induced modification to the electromagnetic form factors of spin-1 particles

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