Heavy QCD axions at high-energy muon colliders

A bstract We study the physics potential of heavy QCD axions at high-energy muon colliders. Unlike typical axion-like particles, heavy QCD axions solve the strong CP problem with phenomenology driven by the anomalous gluon $$ \left( aG\overset{\sim }{G}\right) $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfenced> <mml:mrow> <mml:mi>aG</mml:mi> <mml:mover> <mml:mi>G</mml:mi> <mml:mo>~</mml:mo> </mml:mover> </mml:mrow> </mml:mfenced> </mml:math> couplings. Several ultraviolet scenarios are presented in which QCD axions with TeV-scale masses and decay constants arise consistently with a solution to both the strong CP problem and the axion quality problem. We perform a detailed collider analysis for both a 3 and 10 TeV muon collider, focusing on hadronic axion decays that gives rise to a dijet-resonance signature. Our projections for the axion discovery reach in the multi-TeV mass range demonstrate that a muon collider can significantly extend sensitivity to heavy QCD axions compared to existing experiments.