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ABSTRACT: We consider the infrared sensitivity of the inclusive heavy quark decay width in perturbation theory. It is shown by explicit calculations to the second loop order (when the non-abelian nature of the QCD interactions first become apparent) that all infrared sensitive terms to logarithmic and linear accuracy cancel when the decay width is expressed in terms of the short distance mass. This in turn implies the absense of any non perturbative $1/m_Q$ power corrections to the decay width. The cancellation is shown algebraically at the level of the Feynman integrands without any use of an explicit infrared cutoff. This result is in accord with the implications of the KLN theorem. Comment: 33 pages including figures, revtex with axodraw. Submitted to Phys. Rev. D
04/1998;
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ABSTRACT: We discuss non perturbative corrections to the Coulomb-like potential of heavy quarks at short distances. We consider both the standard framework provided by infrared renormalons and the assumption that confinement does not allow weak fields to penetrate the vacuum. In the former case the leading correction at short distances turns out to be quadratic in r for static quarks. In the latter case we find a potential which is proportional to r as r→0. We point out that similar effects arise due to a new kind of non perturbative correction proportional to 1/Q2, which is unaccounted for by the operator product expansion and which was recently discussed within a different framework. Phenomenological implications of the linear correction to the potential are briefly reviewed.
Physics Letters B. 10/1997;
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ABSTRACT: We review ultraviolet-renormalon physics. This mini-review is intended to be a sequence to the review by the same authors at the “QCD ′96” conference last year.
Nuclear Physics B - Proceedings Supplements. 10/1997;
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ABSTRACT: We present a covariant formulation of the Kinoshita-Lee-Nauenberg (KLN) theorem for processes involving the radiation of soft particles. The role of the disconnected diagrams is explored and a rearrangement of the perturbation theory is performed such that the purely disconnected diagrams are factored out. The remaining effect of the disconnected diagrams results in a simple modification of the usual Feynman rules for the S-matrix elements. As an application, we show that, when combined with the Low theorem, this leads to a proof of the absence of the 1/Q corrections to inclusive processes (such as the Drell-Yan process). In this paper the Abelian case is discussed to all orders in the coupling.
Phys. Rev. D. 06/1997; 56(1).
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ABSTRACT: We argue that the appearance of the Landau pole in the running coupling of QCD introduces 1/Q^2 power corrections in current correlation functions. These terms are not accounted for by the standard operator product expansion and is the price to be paid for the lack of a unique definition of the running coupling at the 1/Q^2 level. We review also possible phenomenological implications of the 1/Q^2 terms in an alternative language of the ultraviolet renormalon. Comment: 7 pages, LaTeX
05/1997;
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ABSTRACT: We discuss the renormalon-based approach to power corrections in non-singlet deep inelastic scattering structure functions and compare it with the general operator product expansion. The renormalon technique and its variations relate the power corrections directly to infrared-sensitive parameters such as the position of the Landau pole \Lambda_{QCD} or the infinitesimal gluon mass \lambda. In terms of the standard OPE these techniques unify evaluations of the coefficient functions and of matrix elements. We argue that in case of deep inelastic scattering there is a proliferation of competeing infrared sensitive parameters. In particular we consider the gluon and quark masses, virtuality of quarks and \Lambda_{QCD} as possible infrared cut offs and compare the emerging results. In the standard renormalon technique where \Lambda_{QCD} is the infrared parameter, the argument of the running coupling is crucial to obtain the correct x dependance of the structure functions. Finally we discuss the limitations of the use of the renormalon based methods for determining of the x dependance of the power corrections.
02/1997;
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ABSTRACT: We present a covariant formulation of the Kinoshita, Lee, Nauenberg (KLN) theorem for processes involving the radiation of soft particles. The role of the disconnected diagrams is explored and a rearrangement of the perturbation theory is performed such that the purely disconnected diagrams are factored out. The remaining effect of the disconnected diagrams results in a simple modification of the usual Feynman rules for the S-matrix elements. As an application, we show that when combined with the Low theorem, this leads to a proof of the absense of the $1/Q$ corrections to inclusive processes (like the Drell-Yan process). In this paper the abelian case is discussed to all orders in the coupling. Comment: 27 pages, LaTeX, 14 figures
02/1997;
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ABSTRACT: We present a sketchy review of renormalon-based phenomenology. In particular, the leading, 1/Q corrections to various observables, KLN cancellations for power-suppressed corrections and the fixation of operator matrix elements are highlighted. Comment: 9 pages, LaTeX file, uses espcrc2.sty
10/1996;
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ABSTRACT: We consider perturbative expansions in theories with an infrared cutoff $\lambda$. The infrared sensitive pieces are defined as terms nonanalytic in the infinitesimal $\lambda^2$ and powers of this cutoff characterize the strength of these infrared contributions. It is argued that the sum over the initial and final degenerate ( as $\lambda \to 0$) states which is required by the Kinoshita - Lee - Nauenberg theorem eliminates terms of order $\lambda^0$ and $\lambda^1$. However, the quadratic and higher order terms in general do not cancel. This is investigated in simple examples of KLN cancellations, of relevance to the inclusive decay rate of a heavy particle, at the one loop level.
10/1996;
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ABSTRACT: We consider corrections to hard processes in QCD where Q is a large mass scale, concentrating on shape variables in e+e− annihilation. While the evidence for such corrections can be and has been established by means of the renormalon technique, theory can be confronted with experiment only after clarifying the properties of the corresponding non-perturbative contribution. We list predictions based on the universality of the terms, and compare them with the existing data. We also identify the scale of the non-perturbative contributions in terms of jet masses.
Nuclear Physics B. 07/1995;
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ABSTRACT: We discuss $1/Q$ corrections to hard processes in QCD where $Q$ is a large mass parameter like the total energy in $e^+e^-$ annihilation. The main problem we address ourselves to is whether these corrections to different processes (concentrating for definiteness on the Thrust and the Drell-Yan cross section) can be related to each other in a reliable way so that the phenomenology of the $1/Q$ corrections can be developed. We derive first the relation valid to lowest order using both the renormalon and finite-gauge-boson mass techniques to check its independence on the infrared cut- off procedure. We then argue that the $1/Q$ corrections are due to soft gluons which factorize into a universal factor such that the lowest order relations are preserved in higher orders. Comment: 12 pages
04/1995;
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ABSTRACT: We discuss corrections to hard processes in QCD where is a large mass parameter like the total energy in e+e− annihilation. The main problem we address ourselves to is whether these corrections to different processes (concentrating for definiteness on the certain event shape variables and the Drell-Yan cross section) can be related to each other in a reliable way so that the phenomenology of the corrections can be developed. We derive first the relation valid to lowest order using both the renormalon and finite-gauge-boson mass techniques to check its independence on the infrared cut-off procedure. We then argue that the corrections are due to soft gluons which factorize into a universal factor such that the lowest order relations are preserved in higher orders.
Physics Letters B.
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ABSTRACT: We present a sketchy review of renormalon-based phenomenology emphasizing the topics discussed in the original papers with the participation of the authors. In particular, the leading, 1/Q corrections to various observables and KLN cancellations for power-suppressed corrections are highlighted.
Nuclear Physics B - Proceedings Supplements.
