Paper

{
  "raw_xml": "<entry>\n    <id>http://arxiv.org/abs/2602.16834v1</id>\n    <title>New Physics and Symmetry Tests with Polarized Photon Fusion and Dipole Moments</title>\n    <updated>2026-02-18T19:59:52Z</updated>\n    <link href='https://arxiv.org/abs/2602.16834v1' rel='alternate' type='text/html'/>\n    <link href='https://arxiv.org/pdf/2602.16834v1' rel='related' title='pdf' type='application/pdf'/>\n    <summary>We discuss new-physics searches and symmetry tests with dipole moments, emphasizing the role of polarization observables. As a primary benchmark, we consider polarized photon fusion in the $e^+ e^-$ environment of the Super Tau-Charm Facility (STCF) and study $γγ\\to τ^+ τ^-$ in the nearly back-to-back region, where a transverse-momentum-dependent (TMD) description provides a convenient framework for organizing polarization effects. We show that linearly polarized photons induce characteristic azimuthal asymmetries in the $τ^+ τ^-$ kinematics, enabling polarization-based observables that enhance sensitivity to the $τ$ electromagnetic dipole form factors. Moreover, $CP$-even and $CP$-odd dipole interactions can be disentangled through distinct angular structures, offering a systematic path to probe $τ$ dipole moments with improved precision at future lepton colliders. As an illustration, we obtain an improved $2σ$ reach on the anomalous magnetic dipole moment, $-4.6 \\times 10^{-3} &lt; \\mathrm{Re}(a_τ) &lt; 7.0 \\times 10^{-3}$, reaching a precision level close to the Standard Model expectation. To place these prospects in a broader context, we briefly summarize the experimental status of dipole-moment measurements across different fermionic systems and highlight their complementarity in constraining new physics. We illustrate this interplay with supersymmetric scenarios featuring $R$-parity violation, in which loop-induced dipole moments provide correlated probes of $CP$-conserving and $CP$-violating interactions. Taken together, polarized photon fusion and precision dipole measurements constitute a coherent program for testing fundamental symmetries and exploring physics beyond the Standard Model.</summary>\n    <category scheme='http://arxiv.org/schemas/atom' term='hep-ph'/>\n    <category scheme='http://arxiv.org/schemas/atom' term='hep-ex'/>\n    <published>2026-02-18T19:59:52Z</published>\n    <arxiv:comment>Proceedings for the 26th International Symposium on Spin Physics (SPIN2025), September 21-26, 2025, Qingdao, China</arxiv:comment>\n    <arxiv:primary_category term='hep-ph'/>\n    <author>\n      <name>Fang Xu</name>\n    </author>\n  </entry>"
}