Probing the coupling of axions to tops and gluons with LHC measurements

A bstract We study axion-like particles (ALPs) whose dominant interactions are with gluons and third-generation quarks, and whose couplings to light Standard Model (SM) particles arise at one loop. These loop-induced effects lead to ALP decays and production channels that can be probed at the LHC, even when tree-level couplings are absent. Using an effective field theory (EFT) description that includes momentum-dependent corrections from radiative effects, we reinterpret a wide range of LHC measurements via the Contur framework to derive model-independent constraints on the ALP parameter space. We show that LHC data place meaningful bounds in the plane of effective couplings $$ {c}_t^0/{f}_a $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>c</mml:mi> <mml:mi>t</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>f</mml:mi> <mml:mi>a</mml:mi> </mml:msub> </mml:math> and $$ {c}_{\overset{\sim }{G}}^0/{f}_a $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>c</mml:mi> <mml:mover> <mml:mi>G</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msubsup> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>f</mml:mi> <mml:mi>a</mml:mi> </mml:msub> </mml:math> , and that these limits are sensitive to the UV origin of the ALP-top and ALP-gluon couplings. We discuss representative scenarios where either $$ {c}_t^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>c</mml:mi> <mml:mi>t</mml:mi> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> or $$ {c}_{\overset{\sim }{G}}^0 $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>c</mml:mi> <mml:mover> <mml:mi>G</mml:mi> <mml:mo>~</mml:mo> </mml:mover> <mml:mn>0</mml:mn> </mml:msubsup> </mml:math> vanishes at the matching scale, and highlight the role of EFT running and mixing in generating observable signals. We also assess the domain of validity of the EFT approach by comparing the typical momentum transfer $$ \sqrt{\hat{s}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mover> <mml:mi>s</mml:mi> <mml:mo>̂</mml:mo> </mml:mover> </mml:msqrt> </mml:math> in sensitive regions to the underlying scale f a . Our results demonstrate the power of loop-aware EFT reinterpretation of SM measurements in probing otherwise elusive ALP scenarios. The framework presented here can be readily extended to include couplings to other fermions and to accommodate ALP decay or long-lived signatures.