Searches for heavy neutrinos at a 3 TeV CLIC in fat jet final states

Heavy Majorana neutrinos ($N$) are predicted in many models of physics beyond the Standard Model. In this work, we explore the production and detection prospects of TeV-scale heavy neutrinos ($m_N \gtrsim 1$ TeV) at a future 3 TeV Compact Linear Collider (CLIC). We focus on two distinct decay topologies: (i) $N \to \ell^{\pm} W^{\mp}$ with hadronic $W$ boson decay, leading to a final state with one charged lepton and a hadronic fat-jet $J_W$; and (ii) $N \to νh$ with subsequent Higgs decay $h \to b\bar{b}$, yielding a Higgs-tagged fat-jet $J_h$ and $\slashed{E}_T$. Based on comprehensive detector-level simulations and background analysis, we present both $2σ$ exclusion limits and $5σ$ discovery reaches in the $m_N$-$|V_{\ell N}|^2$ plane. We further extract 95\% confidence level upper limits on the mixing parameter $|V_{\ell N}|^2$, and perform a detailed comparison with existing constraints from direct searches at future colliders and indirect global fits. Our findings demonstrate that a 3 TeV CLIC can improve the sensitivity to $|V_{\ell N}|^2$ by about two orders of magnitude compared to the projected reaches of future hadron colliders, while remaining competitive with other CLIC search channels.