Probing ALP lepton flavor violation at μTRISTAN

This is the authors' abstract. We don't add key points for this paper.

Axionlike particles (ALPs) with lepton flavor-violating (LFV) interactions are predicted within a wide range of flavored ALP models. The proposed <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>μ</a:mi><a:mi>TRISTAN</a:mi></a:math> high-energy <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msup><c:mi>e</c:mi><c:mo>−</c:mo></c:msup><c:msup><c:mi>μ</c:mi><c:mo>+</c:mo></c:msup></c:math> and <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:msup><e:mi>μ</e:mi><e:mo>+</e:mo></e:msup><e:msup><e:mi>μ</e:mi><e:mo>+</e:mo></e:msup></e:math> collider will provide a good opportunity to explore flavor physics in the charged lepton sector. In this work, based on a model-independent effective Lagrangian describing the ALP leptonic interactions, we investigate the potential of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>μ</g:mi><g:mi>TRISTAN</g:mi></g:math> to probe ALP LFV couplings. We analyze the testability of selected ALP production channels with potential sensitivity at <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>μ</i:mi><i:mi>TRISTAN</i:mi></i:math>, considering different beams and collision energies, including <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:msup><k:mi>e</k:mi><k:mo>−</k:mo></k:msup><k:msup><k:mi>μ</k:mi><k:mo>+</k:mo></k:msup><k:mo stretchy="false">→</k:mo><k:mi>a</k:mi><k:mi>γ</k:mi></k:math>, <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msup><n:mi>e</n:mi><n:mo>−</n:mo></n:msup><n:msup><n:mi>μ</n:mi><n:mo>+</n:mo></n:msup><n:mo stretchy="false">→</n:mo><n:msup><n:mi>e</n:mi><n:mo>−</n:mo></n:msup><n:msup><n:mi>τ</n:mi><n:mo>+</n:mo></n:msup><n:mi>a</n:mi></n:math>, <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:msup><q:mi>μ</q:mi><q:mo>+</q:mo></q:msup><q:msup><q:mi>μ</q:mi><q:mo>+</q:mo></q:msup><q:mo stretchy="false">→</q:mo><q:msup><q:mi>μ</q:mi><q:mo>+</q:mo></q:msup><q:msup><q:mi>τ</q:mi><q:mo>+</q:mo></q:msup><q:mi>a</q:mi></q:math>, and <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:msup><t:mi>e</t:mi><t:mo>−</t:mo></t:msup><t:msup><t:mi>μ</t:mi><t:mo>+</t:mo></t:msup><t:mo stretchy="false">→</t:mo><t:msup><t:mi>τ</t:mi><t:mo>−</t:mo></t:msup><t:msup><t:mi>μ</t:mi><t:mo>+</t:mo></t:msup><t:mi>a</t:mi></t:math>. The produced ALP <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline"><w:mi>a</w:mi></w:math> is either long-lived or can promptly decay to flavor-violating or flavor-conserving charged lepton final states. In particular, combining the above LFV ALP production modes with a suitable LFV decay mode, one can identify signatures that are virtually free of Standard Model background. We show the resulting sensitivity of <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"><y:mi>μ</y:mi><y:mi>TRISTAN</y:mi></y:math> to LFV ALP couplings and compare it with multiple low-energy leptonic constraints and the future improvements thereof. We find that <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mi>μ</ab:mi><ab:mi>TRISTAN</ab:mi></ab:math> can be generally complementary to searches for low-energy LFV processes and measurements of the leptonic magnetic dipole moments and has the capability to explore unconstrained parameter space for ALP masses in the <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"><cb:mrow><cb:mi mathvariant="script">O</cb:mi><cb:mo stretchy="false">(</cb:mo><cb:mn>1</cb:mn><cb:mo stretchy="false">)</cb:mo><cb:mi>–</cb:mi><cb:mi mathvariant="script">O</cb:mi><cb:mo stretchy="false">(</cb:mo><cb:mn>100</cb:mn><cb:mo stretchy="false">)</cb:mo><cb:mtext> </cb:mtext><cb:mtext> </cb:mtext><cb:mi>GeV</cb:mi></cb:mrow></cb:math> range. In the light ALP regime, however, the parameter space that <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"><kb:mi>μ</kb:mi><kb:mi>TRISTAN</kb:mi></kb:math> is sensitive to has been already excluded by low-energy searches for LFV decays.