262 research outputs found
Leptogenesis in the two right-handed neutrino model revisited
We revisit leptogenesis in the minimal non-supersymmetric type I see-saw
mechanism with two right-handed (RH) neutrinos, including flavour effects and
allowing both RH neutrinos N_1 and N_2 to contribute, rather than just the
lightest RH neutrino N_1 that has hitherto been considered. By performing scans
over parameter space in terms of the single complex angle z of the orthogonal
matrix R, for a range of PMNS parameters, we find that in regions around z \sim
\pm \pi/2, for the case of a normal mass hierarchy, the N_2 contribution can
dominate the contribution to leptogenesis, allowing the lightest RH neutrino
mass to be decreased by about an order of magnitude in these regions, down to
M_1 \sim 1.3*10^11 GeV for vanishing initial N_2-abundance, with the numerical
results supported by analytic estimates. We show that the regions around z \sim
\pm \pi /2 correspond to light sequential dominance, so the new results in this
paper may be relevant to unified model building.Comment: 41 pages, 10 figures; v2 matches published version in PR
Right unitarity triangles and tri-bimaximal mixing from discrete symmetries and unification
We propose new classes of models which predict both tri-bimaximal lepton
mixing and a right-angled Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle,
alpha approximately 90 degrees. The ingredients of the models include a
supersymmetric (SUSY) unified gauge group such as SU(5), a discrete family
symmetry such as A4 or S4, a shaping symmetry including products of Z2 and Z4
groups as well as spontaneous CP violation. We show how the vacuum alignment in
such models allows a simple explanation of alpha approximately 90 degrees by a
combination of purely real or purely imaginary vacuum expectation values (vevs)
of the flavons responsible for family symmetry breaking. This leads to quark
mass matrices with 1-3 texture zeros that satisfy the phase sum rule and lepton
mass matrices that satisfy the lepton mixing sum rule together with a new
prediction that the leptonic CP violating oscillation phase is close to either
0, 90, 180, or 270 degrees depending on the model, with neutrino masses being
purely real (no complex Majorana phases). This leads to the possibility of
having right-angled unitarity triangles in both the quark and lepton sectors.Comment: 29 pages, 4 figures, version to be published in NP
Suppressed FCNC in New Physics with Shared Flavor Symmetry
Many extensions of the Standard Model(SM) generate contributions to Flavor
Changing Neutral Current(FCNC) processes that must have sufficient flavor
suppression to be consistent with experiments, if the new physics (NP) is
associated with a scale of a TeV. Here we present a mechanism for suppressing
the NP effects to FCNC processes. We consider the possibility that the source
of NP contributions to FCNC processes share the same flavor symmetry underlying
the SM source of FCNC processes which are the quark and lepton mass matrices.
We call this the principle of shared flavor symmetry. In the flavor symmetric
limit, the quark and lepton mixing matrices have fixed forms and there are no
NP FCNC processes. In the flavor symmetric limit, we take the quark mixing
matrix to be the identity matrix and the lepton mixing matrix to be given by
tri-bimaximal mixing. Realistic mixing matrices are obtained by the small
breaking of the flavor symmetry. New contributions to FCNC processes arise
because of non universal breaking of the flavor symmetry in the quark and
lepton mass matrices and the NP sources of FCNC processes. In particular, we
will focus on new FCNC effects that arise due to the breaking of flavor
symmetry only in the quark and charged lepton mass matrices but not in the NP
sector. In this scenario, NP contributions to FCNC processes is linked to the
source of flavor symmetry breaking in the quark and charged lepton mass
matrices. To demonstrate the mechanism we use a two higgs doublet model as an
example of beyond the SM physics though one should be able to adapt this
mechanism to other models of new physics.Comment: 20 pages, no figure
Starobinsky-like inflation in no-scale supergravity Wess-Zumino model with Polonyi term
We propose a simple modification of the no-scale supergravity Wess-Zumino
model of Starobinsky-like inflation to include a Polonyi term in the
superpotential. The purpose of this term is to provide an explicit mechanism
for supersymmetry breaking at the end of inflation. We show how successful
inflation can be achieved for a gravitino mass satisfying the strict upper
bound TeV, with favoured values
TeV. The model suggests that SUSY may be discovered in collider physics
experiments such as the LHC or the FCC.Comment: 13 pages, 4 figure
Large U_{e3} and Tri-bimaximal Mixing
We investigate in a model-independent way to what extent one can perturb
tri-bimaximal mixing in order to generate a sizable value of |U_{e3}|, while at
the same time keeping solar neutrino mixing near its measured value, which is
close to sin^2 theta_{12} = 1/3. Three straightforward breaking mechanisms to
generate |U_{e3}| of about 0.1 are considered. For charged lepton corrections,
the suppression of a sizable contribution to sin^2 theta_{12} can be achieved
if CP violation in neutrino oscillations is almost maximal. Generation of the
indicated value of |U_{e3}| of about 0.1 through renormalization group
corrections requires the neutrinos to be quasi-degenerate in mass. The
consistency with the allowed range of sin^2 theta_{12} together with large
running of |U_{e3}| forces one of the Majorana phases to be close to pi. This
implies large cancellations in the effective Majorana mass governing
neutrino-less double beta, constraining it to lie near its minimum allowed
value of m_0 cos 2 theta_{12}, where m_0 is greater than about 0.1 eV. Finally,
explicit breaking of the neutrino mass matrix in the inverted hierarchical and
quasi-degenerate neutrino mass spectrum cases is similarly correlated with the
effective Majorana mass, although to a lesser extent. The implied values for
the atmospheric neutrino mixing angle theta_{23} are given in all cases.Comment: 20 pages, 9 figure
Bridging flavour violation and leptogenesis in SU(3) family models
We reconsider basic, in the sense of minimal field content, Pati-Salam x
SU(3) family models which make use of the Type I see-saw mechanism to reproduce
the observed mixing and mass spectrum in the neutrino sector. The goal of this
is to achieve the observed baryon asymmetry through the thermal decay of the
lightest right-handed neutrino and at the same time to be consistent with the
expected experimental lepton flavour violation sensitivity. This kind of models
have been previously considered but it was not possible to achieve a
compatibility among all of the ingredients mentioned above. We describe then
how different SU(3) messengers, the heavy fields that decouple and produce the
right form of the Yukawa couplings together with the scalars breaking the SU(3)
symmetry, can lead to different Yukawa couplings. This in turn implies
different consequences for flavour violation couplings and conditions for
realizing the right amount of baryon asymmetry through the decay of the
lightest right-handed neutrino. Also a highlight of the present work is a new
fit of the Yukawa textures traditionally embedded in SU(3) family models.Comment: 26 pages, 5 figures, Some typos correcte
Flavor Symmetry L_mu - L_tau and quasi-degenerate Neutrinos
Current data implies three simple forms of the neutrino mass matrix, each
corresponding to the conservation of a non-standard lepton charge. While models
based on L_e and L_e - L_mu - L_tau are well-known, little attention has been
paid to L_mu - L_tau. A low energy mass matrix conserving L_mu - L_tau implies
quasi-degenerate light neutrinos. Moreover, it is mu-tau symmetric and
therefore (in contrast to L_e and L_e - L_mu - L_tau) automatically predicts
maximal atmospheric neutrino mixing and zero U_{e3}. A see-saw model based on
L_mu - L_tau is investigated and testable predictions for the neutrino mixing
observables are given. Renormalization group running below and in between the
see-saw scales is taken into account in our analysis, both numerically and
analytically.Comment: 15 pages, 2 figures. Prepared for 5th International Conference on
Nonaccelerator New Physics (NANP 05), Dubna, Russia, 20-25 Jun 200
Renormalization Group Running of Lepton Mixing Parameters in See-Saw Models with Flavor Symmetry
We study the renormalization group running of the tri-bimaximal mixing
predicted by the two typical flavor models at leading order. Although the
textures of the mass matrices are completely different, the evolution of
neutrino mass and mixing parameters is found to display approximately the same
pattern. For both normal hierarchy and inverted hierarchy spectrum, the quantum
corrections to both atmospheric and reactor neutrino mixing angles are so small
that they can be neglected. The evolution of the solar mixing angle
depends on and neutrino mass spectrum, the deviation
from its tri-bimaximal value could be large. Taking into account the
renormalization group running effect, the neutrino spectrum is constrained by
experimental data on in addition to the self-consistency
conditions of the models, and the inverted hierarchy spectrum is disfavored for
large . The evolution of light-neutrino masses is approximately
described by a common scaling factor.Comment: 23 pages, 6figure
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