Effective lepton flavor violating Hℓiℓj vertex from right-handed neutrinos within the mass insertion approximation

Abstract

In this work we present a new computation of the lepton flavor violating Higgs boson decays that are generated radiatively to one-loop from heavy right-handed neutrinos. We work within the context of the inverse seesaw model with three ν R and three extra singlets X, but the results could be generalized to other low scale seesaw models. The novelty of our computation is that it uses a completely different method by means of the mass insertion approximation which works with the electroweak interaction states instead of the usual 9 physical neutrino mass eigenstates of the inverse seesaw model. This method also allows us to write the analytical results explicitly in terms of the most relevant model parameters, that are the neutrino Yukawa coupling matrix Y ν and the right-handed mass matrix M R , which is very convenient for a phenomenological analysis. This Y ν matrix, being generically nondiagonal in flavor space, is the only responsible for the induced charged lepton flavor violating processes of our interest. We perform the calculation of the decay amplitude up to order O(Y 2 ν + Y 4 ν ). We also study numerically the goodness of the mass insertion approximation results. In the last part we present the computation of the relevant one-loop effective vertex H i j for the lepton flavor violating Higgs decay which is derived from a large M R mass expansion of the form factors. We believe that our simple formula found for this effective vertex can be of interest for other researchers who wish to estimate the H → i¯ j rates in a fast way in terms of their own preferred input values for the relevant model parameters Y ν and M

Search for lepton flavour violating decays of the Higgs boson to μτ and eτ in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV

“…These decays are forbidden in the SM but occur in many new physics scenarios. These include supersymmetric [5][6][7][8][9][10][11][12][13], composite Higgs [14,15], or Randall-Sundrum models [16][17][18], SM extensions with more than one Higgs boson doublet [19,20] or with flavour symmetries [21], and many other scenarios [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The presence of LFV Higgs boson couplings would allow τ → µ and τ → e to proceed via a virtual Higgs boson [37,38].…”

Flavor Techniques for LFV Processes: Higgs Decays in a General Seesaw Model

“…The full computation in the neutrino mass basis 1 was done in [9] -see also [7] -, and the final expressions after correcting some typos can be found in [79]. The MIA technique was applied to the particular case of the inverse seesaw model with three pairs of degenerate sterile fermions [13]. Here, we generalize these results to a GSS and discuss how to apply them to the particular case of low scale seesaw models, recovering the results of [13] in the proper limit.…”

“…The fundamental parameters of the model are then the neutrino Yukawa coupling Y ν , which is a 3 × N ν Ra Figure 4: Relevant (dressed) propagators and LFV mass insertion for a general seesaw. All the other Feynman rules needed for the computation of H → k¯ m at one-loop can be found in [13].…”

“…This kind of models are very well motivated from the observation of neutrino oscillations [73][74][75][76], and it is well-known that they may lead to sizable LFV transitions, see for instance the recent review [77] and references therein. Furthermore, it has been shown that the MIA works very well in this context [13,78].…”

“…Furthermore, the LHCb collaboration has also performed similar searches [6]. From the theoretical side, these observables have also been studied very actively, exploring their potential to probe BSM theories such as neutrino mass models [7][8][9][10][11][12][13][14][15], minimal flavor violation [16][17][18][19], supersymmetric models [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38], two Higgs doublet models [39][40][41][42][43], composite Higgs models [44], models with extra dimensions [45][46][47][48], effective Lagrangians [49][50][51][52][53] and ...…”