Probing CP-violating neutral triple gauge couplings at electron-positron colliders

We study the CP-violating (CPV) neutral triple gauge couplings (nTGCs) that can be realized via dimension-8 operators in the Standard Model Effective Field Theory (SMEFT). We present a new formulation of the CPV nTGC form factors that is compatible with the spontaneous breaking of the electroweak gauge symmetry, and show how these CPV form factors can be matched consistently with the corresponding dimension-8 CPV nTGC operators in the broken phase. We then study probes of the CPV nTGCs at future high-energy e⁺e⁻ colliders with centre-of-mass energies \(\sqrt{s}=0.25,0.5,1,3,5\) TeV, respectively, demonstrating that the e^∓ beam polarizations can help to improve the sensitivities of probes of the nTGCs. We estimate that the sensitivity reaches for probing the new physics scales of nTGCs can range from O(TeV) at a 250 GeV e⁺e⁻ collider to O(10 TeV) at an e⁺e⁻ collider of energy 3–5 TeV, and that the sensitivities to the nTGC form factors vary from O(10⁻⁴) to O(10⁻⁶–10⁻⁸) for the e⁺e⁻ collision energy from 250 GeV to 3–5 TeV.