Renormalon

{{Short description|Divergence in perturbative quantum field theory}}

In physics, a renormalon (a term suggested by 't Hooft't Hooft G, in: The whys of subnuclear physics (Erice, 1977), ed. A Zichichi, Plenum Press, New York, 1979.) is a particular source of divergence seen in perturbative approximations to quantum field theories (QFT). When a formally divergent series in a QFT is summed using Borel summation, the associated Borel transform of the series can have singularities as a function of the complex transform parameter.{{cite journal|last=Beneke|first=M.|title=Renormalons|journal=Physics Reports|date=August 1999|volume=37|issue=1–2|pages=1–142|doi=10.1016/S0370-1573(98)00130-6|arxiv = hep-ph/9807443 |bibcode = 1999PhR...317....1B }} The renormalon is a possible type of singularity arising in this complex Borel plane, and is a counterpart of an instanton singularity. Associated with such singularities, renormalon contributions are discussed in the context of quantum chromodynamics (QCD) and usually have the power-like form $\left(\Lambda/Q\right)^p$ as functions of the momentum $Q$ (here $\Lambda$ is the momentum cut-off). They are cited against the usual logarithmic effects like $\ln\left(\Lambda/Q\right)$ .

Brief history

Perturbation series in quantum field theory are usually divergent as was firstly indicated by Freeman Dyson.{{cite journal | last=Dyson | first=F. J. | title=Divergence of Perturbation Theory in Quantum Electrodynamics | journal=Physical Review | publisher=American Physical Society (APS) | volume=85 | issue=4 | date=1952-02-15 | issn=0031-899X | doi=10.1103/physrev.85.631 | pages=631–632}} According to the Lipatov method,L.N. Lipatov, Zh. Eksp. Teor. Fiz. 72, 411(1977) [Sov.Phys. JETP 45, 216 (1977)]. $N$ -th order contribution of perturbation theory into any quantity can be evaluated at large $N$ in the saddle-point approximation for functional integrals and is determined by instanton configurations. This contribution behaves usually as $N!$ in dependence on $N$ and is frequently associated with approximately the same ( $N!$ ) number of Feynman diagrams. Lautrup{{cite journal | last=Lautrup | first=B. | title=On high order estimates in QED | journal=Physics Letters B | publisher=Elsevier BV | volume=69 | issue=1 | year=1977 | issn=0370-2693 | doi=10.1016/0370-2693(77)90145-9 | pages=109–111}} has noted that there exist individual diagrams giving approximately the same contribution. In principle, it is possible that such diagrams are automatically taken into account in Lipatov's calculation, because its interpretation in terms of diagrammatic technique is problematic. However, 't Hooft put forward a conjecture that Lipatov's and Lautrup's contributions are associated with different types of singularities in the Borel plane, the former with instanton ones and the latter with renormalon ones. Existence of instanton singularities is beyond any doubt, while existence of renormalon ones was never proved rigorously in spite of numerous efforts. Among the essential contributions one should mention the application of the operator product expansion, as was suggested by Parisi.{{cite journal | last=Parisi | first=G. | title=Singularities of the Borel transform in renormalizable theories | journal=Physics Letters B | publisher=Elsevier BV | volume=76 | issue=1 | year=1978 | issn=0370-2693 | doi=10.1016/0370-2693(78)90101-6 | pages=65–66}}{{cite journal | last=Parisi | first=G. | title=On infrared divergences | journal=Nuclear Physics B | publisher=Elsevier BV | volume=150 | year=1979 | issn=0550-3213 | doi=10.1016/0550-3213(79)90298-0 | pages=163–172}}

Recently a proof was suggested for absence of renormalon singularities in $\phi^4$ theory and a general criterion for their existence was formulated{{cite journal | last=Suslov | first=I. M. | title=Divergent perturbation series | journal=Journal of Experimental and Theoretical Physics | publisher=Pleiades Publishing Ltd | volume=100 | issue=6 | year=2005 | issn=1063-7761 | doi=10.1134/1.1995802 | pages=1188–1233|arxiv=hep-ph/0510142| s2cid=119707636 }} in terms of the asymptotic behavior of the Gell-Mann–Low function $\beta(g)$ . Analytical results for asymptotics of $\beta(g)$ in $\phi^4$ theory{{cite journal | last=Suslov | first=I. M. | title=Renormalization group functions of the φ⁴ theory in the strong coupling limit: Analytical results | journal=Journal of Experimental and Theoretical Physics | publisher=Pleiades Publishing Ltd | volume=107 | issue=3 | year=2008 | issn=1063-7761 | doi=10.1134/s1063776108090094 | pages=413–429|arxiv=1010.4081| s2cid=119205490 }}{{cite journal | last=Suslov | first=I. M. | title=Asymptotic behavior of the β function in the ϕ⁴ theory: A scheme without complex parameters | journal=Journal of Experimental and Theoretical Physics | volume=111 | issue=3 | year=2010 | issn=1063-7761 | doi=10.1134/s1063776110090153 | pages=450–465|arxiv=1010.4317| s2cid=118545858 }} and QED{{cite journal | last=Suslov | first=I. M. | title=Exact asymptotic form for the β function in quantum electrodynamics | journal=Journal of Experimental and Theoretical Physics | volume=108 | issue=6 | year=2009 | issn=1063-7761 | doi=10.1134/s1063776109060089 | pages=980–984|arxiv=0804.2650| s2cid=56122603 }} indicate the absence of renormalon singularities in these theories.

References

Category:Quantum chromodynamics