Global constraints on a heavy neutrino

Abstract

We estimate constraints on the existence of a heavy, mostly sterile neutrino with mass between 10 eV and 1 TeV. We improve upon previous analyses by performing a global combination and expanding the experimental inputs to simultaneously include tests for lepton universality, lepton flavor violating processes, electroweak precision data, dipole moments, and neutrinoless double beta decay. Assuming the heavy neutrino and its decay products are invisible to detection, we further include, in a self-consistent manner, constraints from direct kinematic searches, the kinematics of muon decay, cosmology, and neutrino oscillations, in order to estimate constraints on the values of |Ue4| 2 , |Uµ4| 2 , and |Uτ4| 2 .

Fully automated precision predictions for heavy neutrino production mechanisms at hadron colliders

“…Extended neutrino mass models [2][3][4][5][6][7][8][9][10] based on the Type I [11][12][13][14][15][16][17][18][19][20], Inverse [21][22][23], and Linear Seesaw Mechanisms [24,25], feature heavy mass eigenstates N i that couple to electroweak (EW) bosons via mixing with left-handed (LH) neutrinos ν L . In these TeVscale scenarios, active-sterile mixing can be as large as |V ℓNi | ∼ 10 −3 − 10 −2 , and consistent with oscillation and EW data [26][27][28], as well as direct searches by the Large Hadron Collider (LHC) experiments [29][30][31]. Thus, if kinematically accessible, hadron colliders can produce heavy neutrinos that decay to lepton number-and/or flavor-violating final states with observable rates.…”

“…Precise values of V ℓN are model-dependent and are constrained by oscillation and collider experiments, tests of lepton universality, and 0νββ-decay [26][27][28]. However, V ℓN factorize in N production cross sections such that…”

Perspectives for tests of neutrino mass generation at the GeV scale: Experimental reach versus theoretical predictions

“…Accelerator-based experiments probe the mass range MeV-TeV depending on the center-of-mass energy available and the process investigated [28][29][30][31][32], just to mention some examples. Additionally, global analyses have investigated the parameter space of the active-sterile mixing in the GeV-TeV range by the use of electroweak (EW) precision observables [33][34][35][36][37][38].…”

Effects of Majorana physics on the UHE $$\nu _{\tau }$$ ν τ flux traversing the Earth

“…As the mixing parameters for the second fermion family with a sterile Majorana neutrino ν μ − ν s are strongly constrained within the framework of 3 + 1 scenarios [7,19], and motivated by the lack of tau-neutrinos in the UHE cosmic flux in IceCube, in this work we study the possibilities that UHE tau-neutrinos from astrophysical sources may provide a signature for Majorana neutrino production by giving a surviving flux after traversing the Earth which may differ from the standard one. In particular the non-observation of a ν τ going up signal could be a manifestation of a sterile neutrino modifying the ν τ flux.…”

“…For Yukawa couplings of order Y ∼ 1, we need a Majorana mass scale of order M N ∼ 10 15 GeV to account for a light ν mass compatible with the current neutrino data (m ν ∼ 0.01 eV), and this fact leads to the decoupling of the Majorana neutrinos. On the other hand, for smaller Yukawa couplings, of the order Y ∼ 10 −8 -10 −6 , sterile neutrinos with masses a e-mail: lduarte@fing.edu.uy b e-mail: sampayo@mdp.edu.ar around M N ∼ (1-1000) GeV could exist, but in the simplest Type-I seesaw scenario with sterile Majorana neutrinos, this leads to a negligible left-right neutrino mixing U 2 lN ∼ m ν /M N ∼ 10 −14 -10 −10 [7][8][9]. Thus, as suggested in [9], the detection of Majorana neutrinos (N ) would be a signal of physics beyond the minimal seesaw mechanism, and its interactions could be better described in a model-independent approach based on an effective theory, considering a scenario with only one Majorana neutrino N and negligible mixing with the ν L .…”