999 research outputs found

### Renormalization of the neutrino mass operators in the multi-Higgs-doublet Standard Model

We derive the renormalization group equations (RGE) for the flavour coupling
matrices of the effective dimension-five operators which yield Majorana
neutrino masses in the multi-Higgs-doublet Standard Model; in particular, we
consider the case where two different scalar doublets occur in those operators.
We also write down the RGE for the scalar-potential quartic couplings and for
the Yukawa couplings of that model, in the absence of quarks. As an application
of the RGE, we consider two models which, based on a mu-tau interchange
symmetry, predict maximal atmospheric neutrino mixing, together with U_{e3} =
0, at the seesaw scale. We estimate the change of those predictions due to the
evolution of the coupling matrices of the effective mass operators from the
seesaw scale down to the electroweak scale. We derive an upper bound on that
change, thereby finding that the radiative corrections to those predictions are
in general negligible.Comment: 16 pages, LaTe

### A non-standard CP transformation leading to maximal atmospheric neutrino mixing

We discuss a neutrino mass matrix $\mathcal{M}_\nu$ originally found by Babu,
Ma, and Valle (BMV) and show that this mass matrix can be characterized by a
simple algebraic relation. From this relation it follows that atmospheric
neutrino mixing is exactly maximal while at the same time an arbitrary mixing
angle $\theta_{13}$ of the lepton mixing matrix $U$ is allowed and--in the
usual phase convention--CP violation in mixing is maximal; moreover, neither
the neutrino mass spectrum nor the solar mixing angle are restricted. We put
forward a simple seesaw extension of the Standard Model where the family lepton
numbers are softly broken by the Majorana mass terms of the right-handed
neutrino singlets and the BMV mass matrix results from a non-standard $CP$
symmetry.Comment: 13 pages, plain LaTeX, no figures; minor modifications, final version
for Phys. Lett.

### Gauge boson families in grand unified theories of fermion masses: E_6^4 x S_4

In third quantization the origin of fermion families is easy to understand:
the electron field, the muon field and the tau field are identical fields in
precisely the same sense as three electrons are identical and undistinguishable
particles of a theory of second quantization. In both cases, the permutation of
these fields or particles leaves the lagrangian invariant. One can also extend
the concept of family to gauge bosons. This can be obtained through the
semidirect product of the gauge group with the group of permutations of n
objects. In this paper we have studied the group E_6^4 x S_4. We explain why we
have chosen E_6 as fundamental gauge group factor and why we start with a model
with four gauge boson/fermion families to accommodate and to fit the standard
model with only three fermion families. We suggest a possible symmetry breaking
pattern of E_6^4 x S_4 that could explain quark, lepton and neutrino masses and
mixings.Comment: 21 pages, no figur

### S3 x Z2 model for neutrino mass matrices

We propose a model for lepton mass matrices based on the seesaw mechanism, a
complex scalar gauge singlet and a horizontal symmetry S_3 \times
\mathbbm{Z}_2. In a suitable weak basis, the charged-lepton mass matrix and
the neutrino Dirac mass matrix are diagonal, but the vacuum expectation value
of the scalar gauge singlet renders the Majorana mass matrix of the
right-handed neutrinos non-diagonal, thereby generating lepton mixing. When the
symmetry $S_3$ is not broken in the scalar potential, the effective
light-neutrino Majorana mass matrix enjoys $\mu$--$\tau$ interchange symmetry,
thus predicting maximal atmospheric neutrino mixing together with $U_{e3} = 0$.
A partial and less predictive form of $\mu$--$\tau$ interchange symmetry is
obtained when the symmetry $S_3$ is softly broken in the scalar potential.
Enlarging the symmetry group S_3 \times \mathbbm{Z}_2 by an additional
discrete electron-number symmetry \mathbbm{Z}_2^{(e)}, a more predicitive
model is obtained, which is in practice indistinguishable from a previous one
based on the group $D_4$.Comment: 13 pages, 3 figures, final version for publication in JHE

### TeV-scale seesaw mechanism catalyzed by the electron mass

We construct a model in which the neutrino Dirac mass terms are of order the
electron mass and the seesaw mechanism proceeds via right-handed neutrinos with
masses of order TeV. In our model the spectra of the three light and of the
three heavy neutrinos are closely related. Since the mixing between light and
heavy neutrinos is small, the model predicts no effects in pp and p \bar p
colliders. Possible signatures of the model are the lepton-number-violating
process e- e- --> H- H-, where H- is a charged scalar particle,
lepton-flavour-violating decays like mu- --> e- e+ e-, or a sizable
contribution to the anomalous magnetic dipole moment of the muon.Comment: 13 pages, one figure, matches published versio

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