250 research outputs found
A relation between CP violation of low energy and leptogenesis
We discuss how CP violation generating lepton number asymmetry can be related
to CP violation in low energy.Comment: A poster Talk presented at KEKTC5, submitted to the proceeding
Higgs Sector of the Minimal Left-Right Symmetric Model
We perform an exhaustive analysis of the most general Higgs sector of the
minimal left-right symmetric model (MLRM). We find that the CP properties of
the vacuum state are connected to the Higgs spectrum: if CP is broken
spontaneously, the MLRM does not approach the Standard Model in the limit of a
decoupling left-right symmetry breaking scale. Depending on the size of the CP
phases scenarios with extra non-decoupling flavor-violating doublet Higgses or
very light SU(2) triplet Higgses emerge, both of which are ruled out by
phenomenology. For zero CP phases the non-standard Higgses decouple only if a
very unnatural fine-tuning condition is fulfilled. We also discuss
generalizations to a non-minimal Higgs sector.Comment: brief discussion of non-minimal Higgs sectors added, journal versio
Complex CKM from Spontaneous CP Violation Without Flavor Changing Neutral Current
We analyse the general constraints on unified gauge models with spontaneous
CP breaking that satisfy the conditions that (i) CP violation in the quark
sector is described by a realistic complex CKM matrix, and (ii) there is no
significant flavor changing neutral current effects in the quark sector. We
show that the crucial requirement in order to conform to the above conditions
is that spontaneous CP breaking occurs at a very high scale by complex vevs of
standard model singlet Higgs fields. Two classes of models are found, one
consisting of pure Higgs extensions and the other one involving fermionic
extensions of the standard model. We give examples of each class and discuss
their possible embeddings into higher unified theories. One of the models has
the interesting property that spontaneous CP violation is triggered by
spontaneous P violation, thereby linking the scale of CP violation to the
seesaw scale for neutrino masses.Comment: Latex file ; 18 pages; No figures; some typos correcte
MeV neutrinos in double beta decay
The effect of Majorana neutrinos in the MeV mass range on the double beta
decay of various isotopes is studied on pure phenomenological arguments. By
using only experimental half life data, limits on the mixing parameter
of the order 10 can be derived. Also the possible
achievements of upcoming experiments and some consequences are outlined.Comment: 7 pages, 6 uudecoded EPS-figure
Possible Z-width probe of a "brane-world" scenario for neutrino masses
The possibility that the accurately known value of the Z width might furnish
information about the coupling of two neutrinos to the Majoron (Nambu-Goldstone
boson of spontaneous lepton number violation) is proposed and investigated in
detail. Both the "ordinary" case and the case in which one adopts a "brane"
world picture with the Majoron free to travel in extra dimensions are studied.
Bounds on the dimensionless coupling constants are obtained, allowing for any
number of extra dimensions and any intrinsic mass scale. These bounds may be
applied to a variety of different Majoron models. If a technically natural
see-saw model is adopted, the predicted coupling constants are far below these
upper bounds. In addition, for this natural model, the effect of extra
dimensions is to decrease the predicted partial Z width, the increase due to
many Kaluza-Klein excitations being compensated by the decrease of their common
coupling constant.Comment: RevTeX, 12 pages, 3 figure
The Problem of Large Leptonic Mixing
Unlike in the quark sector where simple permutation symmetries can
generate the general features of quark masses and mixings, we find it
impossible (under conditions of hierarchy for the charged leptons and without
considering the see-saw mechanism or a more elaborate extension of the SM) to
guarantee large leptonic mixing angles with any general symmetry or
transformation of only known particles. If such symmetries exist, they must be
realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure
Testing quark mass matrices with right-handed mixings
In the standard model, several forms of quark mass matrices which correspond
to the choice of weak bases lead to the same left-handed mixings ,
while the right-handed mixings are not observable quantities. Instead, in
a left-right extension of the standard model, such forms are ansatze and give
different right-handed mixings which are now observable quantities. We
partially select the reliable forms of quark mass matrices by means of
constraints on right-handed mixings in some left-right models, in particular on
. Hermitian matrices are easily excluded.Comment: 12 pages RevTex, no figures. Minor corrections. Comment on SO(10)
changed and one reference adde
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 is not broken in the scalar potential, the effective
light-neutrino Majorana mass matrix enjoys -- interchange symmetry,
thus predicting maximal atmospheric neutrino mixing together with .
A partial and less predictive form of -- interchange symmetry is
obtained when the symmetry 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 .Comment: 13 pages, 3 figures, final version for publication in JHE
Neutrino masses and mixing with seesaw mechanism and universal breaking of extended democracy
In the framework of a minimal extension of the SM, where the only additional
fields are three right-handed neutrinos, we suggest that the charged lepton,
the Dirac neutrino and the right-handed Majorana neutrino mass matrices are
all, to leading approximation, proportional to the democratic matrix. With the
further assumption that the breaking of this extended democracy is universal
for all leptonic mass matrices, a large mixing in the 2-3 sector can be
obtained and is linked to the seesaw mechanism, together with the existence of
a strong hierarchy in the masses of right-handed neutrinos. The structure of
the resulting effective mass matrix of light neutrinos is stable against the
RGE evolution, and a good fit to all solar and atmospheric neutrino data is
obtained.Comment: LaTeX, 17 pages, 2 eps figures. A section on RGE evolution and a few
references added; minor typos correcte
Low scale gravity as the source of neutrino masses?
We address the question whether low-scale gravity alone can generate the
neutrino mass matrix needed to accommodate the observed phenomenology. In
low-scale gravity the neutrino mass matrix in the flavor basis is characterized
by one parameter (the gravity scale M_X) and by an exact or approximate flavor
blindness (namely, all elements of the mass matrix are of comparable size).
Neutrino masses and mixings are consistent with the observational data for
certain values of the matrix elements, but only when the spectrum of mass is
inverted or degenerate. For the latter type of spectra the parameter M_{ee}
probed in double beta experiments and the mass parameter probed by cosmology
are close to existing upper limits.Comment: 10 pages, 1 figur
- âŠ