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

We suggest a supersymmetric (SUSY) explanation of neutrino masses and mixing, where nonrenormalizable interactions in the hidden sector generate lepton number violating Majorana mass terms for both right-chiral sneutrinos and neutrinos. It is found necessary to start with a superpotential including an array of gauge singlet chiral superfields. This leads to nondiagonal ∆L = 2 mass terms and almost diagonal SUSY breaking A-terms. As a result, the observed pattern of bilarge mixing can be naturally explained by the simultaneous existence of the seesaw mechanism and radiatively induced masses. Allowed ranges of parameters in the gauge singlet sector are delineated, corresponding to each of the cases of normal hierarchy, inverted hierarchy and degenerate neutrinos.

We consider the possibility of neutrino mass generation in a supersymmetric model where lepton number can be violated by odd units. The different patterns of mixing in the quark and lepton sectors are attributed to the persence of right-chiral neutrino superfields which (a) enter into Yukawa couplings via non-renormalizable interaction with hidden sector fields, and (b) can violate lepton number by odd units. Both of these features are shown to be the result of some global quantum number which is violated when SUSY is broken in the hidden sector. It is shown how such a scenario, together with all known R-parity violating effects, can lead to neutrino masses and bilarge mixing via seesaw as well as radiative mechanisms. Some sample values of the various parameters involved, consistent with electroweak symmetry breaking constraints, are presented as illustrations.

Supersymmetry offers a cold dark matter candidate, provided that lepton number is not violated by an odd number of units. On the other hand, lepton number violation by even (two) units gives us an attractive mechanism of neutrino mass generation. Here we offer an explanation of this, in a supergravity framework underlying a supersymmetric scenario, the essential feature being particles carrying lepton numbers, which interact only gravitationally with all other known particles. It is shown that one can have the right amount of L 2 effect giving rise to neutrino masses, whereas the lifetime for L 1 decays of the lightest supersymmetric particle can be prolonged beyond the present age of the Universe.

This is the report of flavor physics and model building working group at WHEPP-9. While activities in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently.