Neutral triple gauge couplings (nTGCs) are absent in the standard model effective theory up to dimension-6 operators, but could arise from dimension-8 effective operators. In this work, we study the pure gauge operators of dimension-8 that contribute to nTGCs and are independent of the dimension-8 operator involving the Higgs doublet. We show that the pure gauge operators generate both $Zgamma Z^*$ and $Zgammagamma^*$ vertices with rapid energy dependence $propto E^5$, which can be probed sensitively via the reaction $e^+e^- to Zgamma$. We demonstrate that measuring the nTGCs via the reaction $e^+e^- to Zgamma$ followed by $Z to qbar{q}$ decays can probe the new physics scales of dimension-8 pure gauge operators up to the range $(1-5)$TeV at the CEPC, FCC-ee and ILC colliders with $sqrt{s}=(0.25-1)$TeV, and up to the range $(10-16)$TeV at CLIC with $sqrt{s}=(3-5)$TeV, assuming in each case an integrated luminosity of 5/ab. We compare these sensitivities with the corresponding probes of the dimension-8 nTGC operators involving Higgs doublets and the dimension-8 fermionic contact operators that contribute to the $e^+e^-Zgamma$ vertex.
تحميل البحث