New neutrino interactions at large colliders

Abstract

We update present bounds on the helicity of the neutrinos produced in muon decay, including e + e − → f f LEP 2 data. These significantly reduce the limits derived from all the other electroweak precision data. In Standard Model extensions designed to maximize the RH neutrino * Speaker. † This work has been partially supported by MICINN (FPA2006-05294), Junta de Andalucía (FQM 101, FQM 03048) and the European Union (MRTN-CT-2006-035505).

Multilepton and lepton jet probes of sub-weak-scale right-handed neutrinos

“…The best prospects are in the W ± → µ ± N → µ ± µ ± e ∓ ν final state, which benefits from smaller SM backgrounds due to the lack of an opposite-sign, same-flavor lepton pair. While others have considered trilepton probes of very high mass RH neutrinos, M N 100 GeV [58,59,61,[63][64][65][66][67], our proposal in Section IV is, to our knowledge, the first for the key M N < M W region of parameter space, showing trilepton searches to be potentially more powerful than the current CMS semileptonic searches [38].…”

“…In this high-mass scenario, N are produced through offshell gauge bosons and thus their decay products exhibit very different kinematics from M N < M W . Unlike many trilepton searches that are targeted at discovering Dirac neutrinos or distinguishing between various RH neutrino models [58,59,61,[63][64][65][66][67], we exploit the lepton-numberviolating character of the Majorana neutrinos in fully leptonic decays to improve sensitivity to N . Parts of the parameter space that cannot be discovered at the LHC with our proposals can potentially be probed in future lepton colliders, such as the FCC-ee [68,69].…”

Observable effects of general new scalar particles

“…This is nothing but the well-known seesaw mechanism of type II. Unless the scalar iso-triplet is very heavy (and thus does not contribute to other observables), the smallness of neutrino masses requires that either the lepton Yukawa couplings of the scalar or its linear interactions with the Higgs be tiny [22][23][24].…”

Heavy neutrinos and lepton flavor violation in left-right symmetric models at the LHC

“…Due to QCD radiation, the small inherent widths of the neutrinos of some 10 keV get broadened up to ≈ 50 GeV. As discussed above, we assume negligible left-right mixing, with ζ W , ζ Z and U LR ∼ ζ ν smaller than 10 −4 [68], such that the SM decays N R → W ℓ, Zν, Hν are sufficiently suppressed 4 . For the decays of the heavy W R boson and the neutrino we obtain the branching ratios Br(N R → ℓ qq ′ ) ≈ 83%, for q = u, c, q ′ = d, s, Br(N R → ℓ tb) ≈ 17%, and Br(W R → ℓN R ) ≈ 9% in our benchmark scenario.…”