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α s from τ decays: contour-improved versus fixed-order summation in a new QCD perturbation expansion

  • Irinel Caprini
  • Jan Fischer
Regular Article - Theoretical Physics

Abstract

We consider the determination of α s from τ hadronic decays, by investigating the contour-improved (CI) and the fixed-order (FO) renormalization-group summations in the frame of a new perturbation expansion of QCD, which incorporates in a systematic way the available information about the divergent character of the series. The new expansion functions, which replace the powers of the coupling, are defined by the analytic continuation in the Borel complex plane, achieved through an optimal conformal mapping. Using a physical model recently discussed by Beneke and Jamin, we show that the new CIPT approaches the true results with great precision when the perturbative order is increased, while the new FOPT gives a less accurate description in the regions where the imaginary logarithms present in the expansion of the running coupling are large. With the new expansions, the discrepancy of 0.024 in α s (m τ 2 ) between the standard CI and FO summations is reduced to only 0.009. From the new CIPT we predict α s (m τ 2 )=0.320 −0.009 +0.011 , which practically coincides with the result of the standard FOPT, but which has a more solid theoretical basis.

Keywords

Conformal Mapping True Result Perturbation Expansion Perturbative Order Perturbative Term 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag / Società Italiana di Fisica 2009

Authors and Affiliations

  1. 1.National Institute of Physics and Nuclear EngineeringBucharestRomania
  2. 2.Institute of PhysicsAcademy of Sciences of the Czech RepublicPrague 8Czech Republic

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