Probing new physics in dimension-8 neutral gauge couplings at e+e- colliders

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 Z gamma Z* and Z gamma gamma* vertices with rapid energy dependence proportional to E-5, which can be probed sensitively via the reaction e(+)e(-) -> Z gamma. We demonstrate that measuring the nTGCs via the reaction e(+)e(-) -> Z gamma followed by Z -> q (q) over bar 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 root s = (0.25-1) TeV, and up to the range (10-16) TeV at CLIC with root s = (3-5) TeV, assuming in each case an integrated luminosity of 5 ab(-1). 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(-) Z gamma vertex.

Automated summary

The study demonstrates that dimension-8 pure gauge operators can be sensitively probed through specific reactions, with the potential to detect new physics scales in different ranges at different colliders.