The large coefficient problem; can we make sense out of QCD perturbation theory
There is the possibility of an impending crisis looming on the horizon for QCD. The problem is that in many processes, large coefficients arise in the perturbation series expansion leading to serious uncertainties concerning its predictive power. Until recently most of the examples of such a phenomenon occurred in the calculation of decay rates. These were, by and large, either ignored or dismissed using possible scheme-dependence arguments as a way out. However, more recently a calculation of the 3-loop contribution to the total e{sup +}e{sup -} annihilation cross-section was performed which gave an enormous coefficient of the order of 50 times that of the 2-loop term. If correct, this would imply that the 3-loop contribution actually exceeds that of the 2-loop Thus, from a conservative viewpoint, the validity of the perturbation series expansion as an estimate for the total e{sup +}e{sup -} cross-section is called into question. Since this process has played a key role in the development and understanding of QCD and since, in many ways, it is one of the cleanest methods for extracting {alpha}{sub s} the problem can no longer be avoided. Furthermore, there is no reason to doubt that this problem should occur in all physical processes. Coming to grips with it is, of course, not only important for testing QCD but also for extracting fundamental quantities such as {alpha}{sub s}. Clearly one needs to understand the nature and origin of such large coefficients before one can confidently continue to use perturbative estimates. The purpose of this talk is to focus on these problems. I shall first review the experimental situation with some examples illustrating the problem. I shall then discuss various general components and properties of perturbation theory before attempting to give a possible resolution of the problem. 18 refs., 5 figs.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 5460862
- Report Number(s):
- LA-UR-89-3784; CONF-8907136-2; ON: DE90003212; TRN: 89-031536
- Resource Relation:
- Journal Volume: 233; Conference: NATO advanced research workshop on radiative corrections: results and perspectives, Brighton (UK), 9-14 Jul 1989
- Country of Publication:
- United States
- Language:
- English
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