QCD running, scale and scheme conventions
Research context
postgraduate concept · conditional · As of 2026-10-10
The strong coupling α_s depends on renormalization scale and scheme.
Key knowledge
The strong coupling α_s depends on renormalization scale and scheme. With μ² differentiation, leading running is dα_s/dlnμ²=−(33−2n_f)α_s²/(12π)+higher orders for SU(3). Extraction from collider or lattice observables needs quark-threshold matching, perturbative order, nonperturbative inputs and correlated experimental uncertainties.
Values and equations
α_s=g_s²/(4π); dα_s/dlnμ²=−[(33−2n_f)/(12π)]α_s²+O(α_s³)
- α_s,g_s
- Dimensionless strong couplings
- μ
- Renormalization energy scale GeV (natural units)
- n_f
- Number of active quark flavours
Conditions and scope
- Active flavour number n_f applies between thresholds; leading formula assumes perturbative α_s and uses μ² rather than μ convention.
- Residual scale variation estimates only part of missing-order uncertainty. Different mass definitions and lattice continuum/volume extrapolations must remain identifiable.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected §§9.1.1–9.1.2, 9.2 and 9.4: scale/scheme dependence, masses, perturbative observables and coupling extraction; rolling URL checked 2026-10-10; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication.
2026-10-10 · Author source inspection of the displayed claim, model assumptions and equations; independent exact-content and branch-inventory review is a separate gate. Contemporary status is a dated snapshot, not a promise of ongoing monitoring.
Entry details
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- research-physics-qcd-running-scheme
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- research.1
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- Postgraduate & research reference