ρ parameter and H 0 → ℓ i ℓ j in models with TeV sterile neutrinos

Abstract

The presence of massive sterile neutrinos N mixed with the active ones induces flavor violating processes in the charged lepton sector at the loop level. In particular, the amplitude of H 0 → ¯ ℓ i ℓ j is expected to be proportional to the product of heavy-light Yukawa couplings y i y j = 2 s ν i s ν j m 2 N / v 2 , where s ν i , j express the heavy-light neutrino mixings. Here, we revisit these Higgs decays in the most generic extension of the neutrino sector, focusing on large values of y i . We show that decoupling effects and a cancellation between the two dominant contributions to these processes makes the amplitude about 100 times smaller than anticipated. We find that perturbative values of y i giving an acceptable contribution to the ρ parameter imply B ( H 0 → ¯ ℓ i ℓ j ) < 10 − 8 for any lepton flavors, a rate that is not accessible at current colliders.