Renormalisation group and universality limits
Research context
research method · conditional · As of 2026-10-10
Coarse-graining changes couplings while preserving long-distance observables after rescaling.
Key knowledge
Coarse-graining changes couplings while preserving long-distance observables after rescaling. Relevant directions grow near a fixed point and require tuning; irrelevant directions shrink. For short-range scalar φ⁴ criticality, four spatial dimensions is the upper critical dimension; below it the interacting fixed point corrects mean-field exponents, while d=4 has marginal logarithmic corrections.
Conditions and scope
- Equilibrium classical short-range scalar field; statements about d=4 are not a rule for all transitions.
- An ε=4−d expansion is controlled for small ε; extrapolating to d=3 or 2 requires additional evidence. Measured universality requires the correct symmetries and relevant perturbations.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected §§3.1–3.4: coarse-graining, relevant directions, upper critical dimension and Wilson–Fisher expansion; 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-renormalisation-criticality
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- Postgraduate & research reference