Modified contour-improved perturbation theory

Cvetič, Gorazd; Loewe, M.; Martínez, Cristián; Valenzuela, Cristina Ofelia

doi:10.1103/physrevd.82.093007

Cited by 46 publications

(68 citation statements)

References 36 publications

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“…The inclusion of the recently computed α 4 s correction [21] to R τ rendered the discrepancy between FOPT and CIPT even more pronounced. Since then, several works have dealt with the RG improvement of the series [18,[22][23][24][25][26]. A difficulty common to all these works is that conclusions in favour of FOPT or CIPT (or a third prescription) depend on implicit or explicit assumptions on the yet unknown higher order coefficients of the Adler function.…”

Section: Introductionmentioning

confidence: 99%

Perturbative expansion of τ hadronic spectral function moments and α s extractions

Beneke

Boito

Jamin

2013

J. High Energ. Phys.

173

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Various moments of the hadronic spectral functions have been employed in the determination of the strong coupling α s from tau decays. In this work we study the behaviour of their perturbative series under different assumptions for the large-order behaviour of the Adler function, extending previous work on the tau hadronic width. We find that the moments can be divided into a small number of classes, whose characteristics depend only on generic features of the moment weight function and Adler function series. Some moments that are commonly employed in α s analyses from τ decays should be avoided because of their perturbative instability. This conclusion is corroborated by a simplified α s extraction from individual moments. Furthermore, under reasonable assumptions for the higher-order behaviour of the perturbative series, fixed-order perturbation theory (FOPT) provides the preferred framework for the renormalization group improvement of all moments that show good perturbative behaviour. Finally, we provide further evidence for the plausibility of the description of the Adler function in terms of a small number of leading renormalon singularities.

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Section: Introductionmentioning

confidence: 99%

Perturbative expansion of τ hadronic spectral function moments and α s extractions

Beneke

Boito

Jamin

2013

J. High Energ. Phys.

173

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“…The recent calculation of the Adler function to four loops [1], the same order to which the -function of the renormalization-group (RG) equation is known [2,3], renewed interest in the determination of s ðM 2 Þ [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The intriguing remark [6] that the inclusion of a higherorder term increased, instead of reducing, the theoretical error on the resulting s ðM 2 Þ stimulated many investigations aimed at understanding this fact.…”

Section: Introductionmentioning

confidence: 99%

“…They include in general additional information about the series beyond the truncation order, known either from specific classes of Feynman diagrams or from RG invariance. Thus, a reordering of the standard contour-improved approach exploiting RG invariance was proposed in [11], and a detailed analysis of the errors of various expansions has been performed in [9].…”

Section: Introductionmentioning

confidence: 99%

Determination ofαs(Mτ2)from improved fixed order perturbation theory

2012

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We revisit the extraction of s ðM 2 Þ from the QCD perturbative corrections to the hadronic branching ratio, using an improved fixed-order perturbation theory based on the explicit summation of all renormalization-group accessible logarithms, proposed some time ago in the literature. In this approach, the powers of the coupling in the expansion of the QCD Adler function are multiplied by a set of functions D n , which depend themselves on the coupling and can be written in a closed form by iteratively solving a sequence of differential equations. We find that the new expansion has an improved behavior in the complex energy plane compared to that of the standard fixed-order perturbation theory (FOPT), and is similar but not identical to the contour-improved perturbation theory (CIPT). With five terms in the perturbative expansion we obtain in the MS scheme s ðM 2 Þ ¼ 0:338 AE 0:010, using as input a precise value for the perturbative contribution to the hadronic width of the lepton reported recently in the literature.

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“…1 (a) and (b). According to theoretical calculations, with a heavy Majorana neutrino of mass within the (2 − 4) GeV/c 2 range, the branching fractions of B + → D − ℓ + ℓ ′+ can be larger than 10 −7 [4,5] with the diagram in Fig. 1 (b) giving the dominant contribution.…”

Section: Introductionmentioning

confidence: 99%