Neutrino masses and lepton-number violation in the littlest Higgs scenario

Abstract

We investigate the sources of neutrino mass generation in Little Higgs theories, by confining ourselves to the "Littlest Higgs" scenario. Our conclusion is that the most satisfactory way of incorporating neutrino masses is to include a lepton-number violating interaction between the scalar triplet and lepton doublets. The tree-level neutrino masses generated by the vacuum expectation value of the triplet are found to dominate over contributions from dimension-five operators so long as no additional large lepton-number violating physics exists at the cut-off scale of the effective theory. We also calculate the various decay branching ratios of the charged and neutral scalar triplet states, in regions of the parameter space consistent with the observed neutrino masses, hoping to search for signals of lepton-number violating interactions in collider experiments. Little Higgs theories [1, 2, 3] represent a new attempt to address the problem of quadratic divergence in the mass of the Higgs boson responsible for electroweak symmetry breaking. This approach treats the Higgs boson as part of an assortment of pseudo-Goldstone bosons, arising from a global symmetry spontaneously broken at an energy scale Λ, typically on the order of 10 TeV. There is also an explicit breakdown of the overseeing global symmetry via gauge and Yukawa interactions, thereby endowing the Goldstone bosons with a Coleman-Weinberg potential and making them massive. The Higgs mass is thus protected by the global symmetries of the theory and only arises radiatively due to the gauge and Yukawa interactions. As an effective theory valid up to the scale Λ, the model is rather economical in terms of the new fields introduced in order to fulfill the necessary cancellation for the quadratic divergence at the one-loop level. The model requires, in addition to new gauge bosons and vectorlike fermions, the existence of additional scalars belonging to certain representations of the Standard Model (SM) gauge group.Aside from the crucial vector-like T -quark, the fermionic sector can essentially have the

LeptonicCPviolation

“…Provided the triplet VEV is small enough, the decays of ∆ ±± → l ± l ± are dominant over ∆ ++ → ∆ + ∆ + , ∆ ++ → ∆ + W + and ∆ ++ → W + W + . In this case, the decay of the ∆ ±± pair into four charged leptons gives a very clear signature, which is almost free of any SM background (del Aguila and Aguilar-Saavedra, 2009; Han et al, 2005).…”

“…In particular, if the neutrino mass mechanism operates at scales not far from the electroweak scale, then new phenomena can manifest in colliders. Most of the research performed in this direction concerns the study of new signals, which result from decays of the seesaw mediators (del Aguila and AguilarSaavedra, 2009; Akeroyd et al, 2008;Han et al, 2005;Kadastik et al, 2008). Although these decays do not lead to explicit CPV effects, the presence of CPV phases affects the decay rates, since the couplings of the SM particles to the seesaw mediators depend on the phases α 1,2 and δ of the lepton mixing matrix U.…”

Doubly charged scalar decays in a type II seesaw scenario with two Higgs triplets

“…Alternatively, the decay into a pair of same-sign W bosons, i.e. ∆ ++ → W + W + , is dominant in a complementary region of the parameter space, which -though more challenging from the viewpoint of background elimination -can unravel a doubly-charged scalar [14][15][16][17][18][19][20][21][22][23].…”

Flavor physics of leptons and dipole moments

“…An important open issue to address in the context of Little Higgs models is the origin of non-zero neutrino masses [642][643][644][645][646]. The neutrino mass mechanism which naturally occurs in these models is the triplet Higgs mechanism [234] which employs a scalar with the SU (2) L U (1) Y quantum numbers T (3;2).…”