Direct searches of Type-III seesaw triplet fermions at high energy e+e- collider

The signatures of heavy fermionic isotriplets ( Σ ) are probed through their direct production and subsequent decay at high energy electron–positron colliders. Unlike the case of LHC, the production process has strong dependence on the mixing of Σ with electron ( V e ), making the leptonic collider unique to fingerprint the presence of such mixing. We establish that pair production considered at s = 2 TeV can be employed to study both the cases of V e = 0 and of V e ≠ 0 with ∼ 100 fb - 1 luminosity, while the single production can probe the latter case with a few inverse femto barn luminosity at s = 1 TeV. Exploring the mass reach, both the single and pair productions are capable of probing Σ of mass close to the kinematic limits through selected channels. Investigating simultaneous limits on the M Σ - V e parameter space, we identify suitable final states and their 3 σ reach on V e and M Σ at 300 (100) fb - 1 luminosity in the case of pair (single) Σ production.