A QCD axion dynamically relaxes the strong-CP angle.

Nature contains a canonically normalized dynamical pseudoscalar a with gluonic interaction (alpha_s/(8*pi))*(theta_bar+a/fa)*G*Gtilde, where fa includes the color-anomaly coefficient. Its pure-QCD vacuum energy is minimized at theta_bar+a/fa=0 modulo 2*pi. At zero temperature its QCD-induced mass contribution obeys m_a,QCD^2*fa^2=chi_QCD, where chi_QCD is the second derivative of pure-QCD vacuum energy with respect to theta at zero. This is a statement about the QCD contribution, not an exact equality for the total mass in the presence of other potentials. Calculable weak-interaction CP-violating shifts of the total minimum are allowed; an exactly CP-conserving full Standard Model vacuum is not required. A photon-only axion-like particle is insufficient.

YES: Independent replicated measurements establish the normalized gluonic coupling and a QCD-induced potential with the stated minimum and curvature, allowing propagated theoretical/experimental uncertainties and calculated weak CP corrections. Any measured total mass must be decomposed consistently if additional potential terms are present; a mass/photon signal alone is insufficient. Each detection must reject its stated backgrounds globally at >= 5 sigma. NO: A verified microscopic account of strong CP plus independent tests excludes the specified dynamical mechanism, not merely a benchmark axion model. Searches over finite mass/coupling ranges, or discovery of another CP mechanism without excluding coexistence, leave this market UNDECIDED. Reference sources: PDG: Axions and other similar particles (https://pdg.lbl.gov/2025/reviews/rpp2025-rev-axions.pdf); Bertolini, Di Luzio and Nesti: axion-mediated forces and CP violation (https://arxiv.org/abs/2006.12508). Evidence policy: use public primary research with methods and uncertainty, plus the named reference sources below. A preprint can inform the estimate but cannot alone meet a terminal criterion; require a peer-reviewed primary result and an independent reproduction using non-overlapping observations or independently prepared samples, unless this is a mathematical proof or the specific criterion instead requires independently implemented calculations. Report data provenance, exclusions, calibration, statistical model and systematic uncertainty. Independence means different data acquisition, not two papers reanalysing the same sample. For a quantitative terminal test, both independent results must meet the stated threshold; disagreement or an interval crossing the boundary means UNDECIDED. Use the final corrected version public at the signed round's evidence cutoff (UTC); exclude later evidence until a later eligible round. Every report in a terminal round must use the same cutoff, covered by the verified signed context and enforced by the configured terminal protocol; a different cutoff requires a new eligible round, never reinterpretation of a signed report or mutation of an immutable binding. This market has no calendar expiry. Retracted findings cannot supply a terminal result. If a named source disappears, use its DOI/publisher or an archived identical version, then an equivalent primary publication applying these unchanged definitions; if none is accessible, remain UNDECIDED, never substitute a different test. Missing data, failed replication, a null search outside the specified domain, or an untested alternative is not automatically NO. These are instructions for evidence assessment, not an automatic truth oracle: scientific interpretation and systematic-error judgment remain. Settlement follows the configured platform mode: terminal mode requires one valid round with all three frozen models returning the same explicit YES or NO and criterion_met=true; any UNDECIDED, failure or disagreement leaves it unresolved. Legacy proposal/challenge mode requires its recorded review process. Model agreement does not prove scientific truth. Invalidity is not NO and this text does not authorize a refund or cancellation: only a cancellation rule disclosed before exposure, if the configured contract supports it, can apply. Otherwise pause new entries and preserve holders' existing rights. Never reinterpret terms after listing.