784 research outputs found
Minimal Lepton Flavour Violation and Leptogenesis with exclusively low-energy CP Violation
We study the implications of a successful leptogenesis within the framework
of Minimal Lepton Flavour Violation combined with radiative resonant
leptogenesis and the PMNS matrix being the only source of CP violation, which
can be obtained provided flavour effects are taken into account. We find that
the right amount of the baryon asymmetry of the universe can be generated under
the conditions of a normal hierarchy of the light neutrino masses, a
non-vanishing Majorana phase, sin(theta_{13})>0.13 and m_{nu,lightest}<0.04 eV.
If this is fulfilled, we find strong correlations among ratios of charged LFV
processes.Comment: published in JHEP, small change
Leptogenesis with exclusively low-energy CP Violation in the Context of Minimal Lepton Flavour Violation
We analyze lepton flavour violation (LFV) and the generation of the observed
baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal
lepton flavour violation framework with three quasi-degenerate heavy Majorana
neutrinos. The BAU which is obtained through radiative resonant leptogenesis
can successfully be generated widely independent of the Majorana scale in this
scenario and flavour effects are found to be relevant. Then we discuss the
specific case in which CP violation is exclusively present at low-energies (a
real R matrix) in the flavour sensitive temperature regime. Successful
leptogenesis in this case leads to strong constraints on low-energy neutrino
parameters.Comment: Contrubution to the proceedings of the EPS HEP 2007 conference,
Manchester (UK). 3 pages, 3 figure
Addendum to Finite-size effects on multibody neutrino exchange
The interaction energy of the neutrons due to massless neutrino exchange in a
neutron star has recently been proved, using an effective theory, to be
extremely small and infrared-safe. Our comment here is of conceptual order: two
approaches to compute the total interaction energy density have recently been
proposed. Here, we study the connection between these two approaches. From CP
invariance, we argue that the resulting interaction energy has to be even in
the parameter , which expresses the static neutrino
potential created by a neutron medium of density .Comment: Latex file (Revtex), 9 pages, 1 figure, one reference change
On the Role of Low-Energy CP Violation in Leptogenesis
The link between low-energy CP violation and leptogenesis became more
accessible with the understanding of flavor effects. However, a definite
well-motivated model where such a link occurs was still lacking. Adjoint SU(5)
is a simple grand unified theory where neutrino masses are generated through
the Type I and Type III seesaw mechanisms, and the lepton asymmetry is
generated by the fermionic triplet responsible for the Type III seesaw. We
focus exclusively on the case of inverted hierarchy for neutrinos, and we show
that successful flavored leptogenesis in this theory strongly points towards
low-energy CP violation. Moreover, since the range of allowed masses for the
triplet is very restricted, we find that the discovery at the LHC of new states
present in the theory, together with proton decay and unification of gauge
couplings, can conspire to provide a hint in favor of leptogenesis.Comment: 12 pages, 6 figure
Study of flavour dependencies in leptogenesis
We study the impact of flavours on the efficiency factors and give analytical
and numerical results of the baryon asymmetry taking into account the different
charged lepton Yukawa contributions and the complete (diagonal and
off-diagonal) to conversion matrix. With this treatment we update
the lower bound on the lightest right-handed neutrino mass.Comment: 13 pages, 11 figures. typos corrected, some formulae modified. 2
figures and discussion adde
Neutrinos in the simplest little Higgs scenario and TeV leptogenesis
The little Higgs scenario may provide an interesting framework to accommodate
TeV scale leptogenesis because a TeV Majorana mass of the right-handed neutrino
that we employ for the latter may find a natural place near the ultraviolet
cutoff of the former. In this work we study how a light neutrino spectrum,
generated radiatively, and TeV scale leptogenesis can be embedded in the
simplest little
Higgs framework. Alternatively, we highlight how the neutrino Yukawa textures
of the latter are constrained.Comment: 10 pages, latex, v2: refs and comments added, to appear in PR
Leptogenesis in SO(10) models with a left-right symmetric seesaw mechanism
We study leptogenesis in supersymmetric SO(10) models with a left-right
symmetric seesaw mechanism, including flavour effects and the contribution of
the next-to-lightest right-handed neutrino. Assuming M_D = M_u and hierarchical
light neutrino masses, we find that successful leptogenesis is possible for 4
out of the 8 right-handed neutrino mass spectra that are compatible with the
observed neutrino data. An accurate description of charged fermion masses
appears to be an important ingredient in the analysis.Comment: Submitted for the SUSY07 proceedings, 4 pages, 9 figure
Dirac phase leptogenesis
I present here a concise summary of the preprint arXiv:0707.3024, written in
collaboration with A. Anisimov and P. Di Bari. There we discuss leptogenesis
when {\em CP} violation stems exlusively from the Dirac phase in the PMNS
mixing matrix. Under this assumption it turns out that the situation is very
constrained when a hierarchical heavy right-handed (RH) neutrino spectrum is
considered: the allowed regions are small and the final asymmetry depends on
the initial conditions. On the other hand, for a quasi-degenerate spectrum of
RH neutrinos, the {\em CP} asymmetry can be enhanced and the situation becomes
much more favorable, with no dependence on the initial conditions.
Interestingly, in the extreme case of resonant leptogenesis, in order to match
the observed baryon asymmetry of the Universe, we obtain a lower bound on \sin
\q_{13} which depends on the lightest active neutrino mass m_1.Comment: 3 pages, 2 figures, contribution to the proceedings of the TAUP 07
conference, Sep. 11-15, Sendai, Japa
Full Boltzmann equations for leptogenesis including scattering
We study the evolution of a cosmological baryon asymmetry produced via
leptogenesis by means of the full classical Boltzmann equations, without the
assumption of kinetic equilibrium and including all quantum statistical
factors. Beginning with the full mode equations we derive the usual equations
of motion for the right-handed neutrino number density and integrated lepton
asymmetry, and show explicitly the impact of each assumption on these
quantities. For the first time, we investigate also the effects of scattering
of the right-handed neutrino with the top quark to leading order in the Yukawa
couplings by means of the full Boltzmann equations. We find that in our full
Boltzmann treatment the final lepton asymmetry can be suppressed by as much as
a factor of 1.5 in the weak wash-out regime (K<1), compared to the usual
integrated approach which assumes kinetic equilibrium and neglects quantum
statistics. This suppression is in contrast with the enhancement seen in some
previous studies that considered only decay and inverse decay of the
right-handed neutrino. However, this suppression quickly decreases as we
increase K. In the strong wash-out regime (K>1), the full Boltzmann treatment
and the integrated approach give nearly identical final lepton asymmetries
(within 10 % of each other at K>3). Finally, we show that the opposing effects
of quantum statistics on decays/inverse decays and the scattering processes
tend to reduce the net importance of scattering on leptogenesis in the full
treatment compared to the integrated approach.Comment: 39 pages, 8 figures, typos corrected, replaced to match published
versio
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