Conjectures about the Chiral Phase Transition in QCD from Anomalous Multi-Instanton Interactions

To date numerical simulations of lattice QCD have not found a chiral phase transition of first order that is expected to occur for sufficiently light pions. We show how the restoration of an exact global chiral symmetry can strongly decrease the breaking of the approximate, anomalous <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>U</a:mi><a:mi>A</a:mi></a:msub><a:mo stretchy="false">(</a:mo><a:mn>1</a:mn><a:mo stretchy="false">)</a:mo></a:math> symmetry. This is testable on the lattice through simulations for one through four flavors. In QCD a small breaking of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msub><e:mi>U</e:mi><e:mi>A</e:mi></e:msub><e:mo stretchy="false">(</e:mo><e:mn>1</e:mn><e:mo stretchy="false">)</e:mo></e:math> symmetry in the chirally symmetric phase generates novel experimental signals. Published by the American Physical Society 2024