Dynamical Minimal Flavour Violating Inverse Seesaw

Abstract

The Inverse Seesaw mechanism is dynamically realised within the Minimal Lepton Flavour Violation context. Lepton number, whose breaking is spontaneously realised, is generalised to a global Abelian factor of the whole flavour symmetry, that also plays the role of the Peccei-Quinn symmetry. The associated Goldstone boson is a Majoraxion that solves the Strong CP problem and represents a Dark Matter candidate.Three distinct scenarios are identified in terms of flavour symmetry and transformation properties of the exotic neutral leptons that enrich the Standard Model spectrum. The associated phenomenology is studied, focusing on the deviations from unitarity of the PMNS mixing matrix. The strongest constraints arise from the determination of the number of active neutrinos through the invisible width of the Z, the comparison of the measured W boson mass with its prediction in terms of the Fermi constant from muon decay, and the null searches for the radiative rare muon decay and µ → e conversion in nuclei. The heavy neutral leptons may have masses of a few TeV, leaving open the possibility for a direct detection at future colliders.The impact of the recent measurement of the W mass at the CDF II detector has also been considered, which, in one of the scenarios, points to a sharp prediction for the masses of the heavy neutral leptons at about 2 − 3 TeV.

Consistency of New CDF-II W Boson Mass with 123-Model

“…Its scalar sector contains three CP-even Higgs bosons, h 1 , h 2 and h 3 , one CP-odd Higgs boson, A, a pair of charged Higgs bosons, H ± , and a pair of double-charged Higgs bosons, H ±± . Recently, several novel physics models, including the : Two-Higgs doublet model [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], Higgs triplet model [21][22][23][24][25], supersymmetry [26][27][28][29][30], leptoquark model [31][32][33], seesaw mechanism [34][35][36][37][38], vector-like leptons and/or vector-like quarks [39][40][41][42] and other SM extensions [43][44][45][46][47][48][49][50][51][52][53]…”

The Low‐Scale Seesaw Solution to the MW$M_W$ and (g−2)μ$(g-2)_\umu$ Anomalies

“…showing a 7𝜎 discrepancy relative to the SM prediction. 1 Among the numerous proposals to explain such a tension, the class of the so-called Low-Scale Seesaw (SS) mechanisms [4,5] represents a very appealing possibility, [6,7] as it also provides a description for massive neutrinos. In the generic model of this type, two kinds of exotic neutral leptons, N R and S R in the following, with opposite lepton numbers, are added to the SM spectrum.…”

“…The number of the exotic neutral leptons of each type depends on the specific realisation: for example, in Ref. [7], three N R and three S R have been considered in the exotic spectrum. In general, for an arbitrary number of N R and of S R , it is convenient to adopt a compact notation for all the neutral leptons, SM and exotic, defining a multidimensional vector in the flavour space 1 𝜒 ≡ (𝜈 L , N c R , S c R ) T , (…”

“…This is particularly interesting due to the significant induced deviation from the unitarity of the PMNS matrix, [17][18][19][20] which translates into a tree-level contribution to M W and allows to solve the CDF II anomaly, as discussed in Refs. [6,7]. Indeed, any modification of the leptonic charged current implies an additional contribution to the muon 𝛽 decay, from which the value of the Fermi Constant G F (defined as the parameter that enters the Fermi Lagrangian) is computed: labelling with G μ the parameter extracted from the muon lifetime,…”

Axion-like ALPs

“…Notice that we are considering the case of massless neutrinos, which will therefore not couple to the ALP at tree level. Examples of axion models where a Seesaw is implemented can be found in Refs [26][27][28][29][30][31][32][33][30,[35][36][37][38][39].…”