Probing New Physics in Dimension-8 Neutral Gauge Couplings at $e^+e^-$ Colliders

Understand

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 $\propto E^5$, which can be probed sensitively via the reaction $e^+e^- \to Z\gamma$.
• We demonstrate that measuring the nTGCs via the reaction $e^+e^- \to Z\gamma$ followed by $Z \to q\bar{q}$ 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.