406 research outputs found
Leptogenesis in the presence of exact flavor symmetries
In models with flavor symmetries in the leptonic sector leptogenesis can take
place in a very different way compared to the standard leptogenesis scenario.
We study the generation of a asymmetry in these kind of models in the
flavor symmetric phase pointing out that successful leptogenesis requires (i)
the right-handed neutrinos to lie in different representations of the flavor
group; (ii) the flavons to be lighter at least that one of the right-handed
neutrino representations. When these conditions are satisfied leptogenesis
proceeds due to new contributions to the CP violating asymmetry and -depending
on the specific model- in several stages. We demonstrate the validity of these
arguments by studying in detail the generation of the asymmetry in a
scenario of a concrete flavor model realization.Comment: 25 pages, 7 figures; version 2: A few clarifications added. Version
matches publication in JHE
Experimental tests for the Babu-Zee two-loop model of Majorana neutrino masses
The smallness of the observed neutrino masses might have a radiative origin.
Here we revisit a specific two-loop model of neutrino mass, independently
proposed by Babu and Zee. We point out that current constraints from neutrino
data can be used to derive strict lower limits on the branching ratio of
flavour changing charged lepton decays, such as .
Non-observation of Br() at the level of would rule
out singly charged scalar masses smaller than 590 GeV (5.04 TeV) in case of
normal (inverse) neutrino mass hierarchy. Conversely, decay branching ratios of
the non-standard scalars of the model can be fixed by the measured neutrino
angles (and mass scale). Thus, if the scalars of the model are light enough to
be produced at the LHC or ILC, measuring their decay properties would serve as
a direct test of the model as the origin of neutrino masses.Comment: 14 pages, 16 figure
Towards spin injection from silicon into topological insulators: Schottky barrier between Si and Bi2Se3
A scheme is proposed to electrically measure the spin-momentum coupling in
the topological insulator surface state by injection of spin polarized
electrons from silicon. As a first approach, devices were fabricated consisting
of thin (<100nm) exfoliated crystals of Bi2Se3 on n-type silicon with
independent electrical contacts to silicon and Bi2Se3. Analysis of the
temperature dependence of thermionic emission in reverse bias indicates a
barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky
barrier opens the possibility of novel device designs based on sub-band gap
internal photoemission from Bi2Se3 into Si
Efecto del polimorfismo de interleuquina 1-beta en el tiempo de tratamiento de pacientes sometidos a una técnica de piezocisión modificado
Objetivo: Evaluar la correlación entre el polimorfismo de la IL1-ß (interleukin 1 beta [Homo sapiens (human)]+3954) y la velocidad de movimiento dentario expresada en tiempo total de tratamiento, y tiempo total de alineamiento, en un grupo de pacientes sometidos a técnicas de aceleración de movimiento (Decorticación alveolar selectiva en abordaje tipo piezocisión con y sin el uso de una matriz colágenas 3D de origen porcino (Mucograft®). Diseño: Anidado a un ensayo clínico controlado, con 40 pacientes voluntarios sanos, estables periodontalmente, que presentaban maloclusión de Clase I con apiñamiento grado II o III y que requerían tratamiento de ortodoncia. Se aisló el ADN de una muestra de sangre mediante el estuche Quick DNA miniprep plus (Zymo D4068). Para detectar el polimorfismo genético del nucleótido +3954 C>T en el gen de la interleuquina 1 beta (IL-1ß), se utilizó un ensayo de PCR en tiempo real prediseñado TaqMan® de genotipificación de polimorfismo de nucleótico único (SNP) para IL-1 ß (rs1143634) de Applied Biosystems (ABI). Resultados: 37 participantes completaron el estudio, con edad promedio de 25.45±6.23 y el 29.73% fueron mujeres. La duración media de tratamiento ortodóntico completo fue 409.62±120.29 días. En 11 individuos el alelo 2 (T) fue heterocigota junto con el alelo 1 (T/C) y 26 individuos todos fueron homocigotos para el alelo 1 (C/C). Ningún sujeto resultó homocigoto para el SNP (T/T). Las características inmunológicas del paciente permiten el diagnóstico y posible manejo terapéutico genético son el futuro de tratamientos ortodónticos más exitosos centrados en los pacientes y sus necesidades.MaestríaMAGISTER EN CIENCIAS ODONTOLÓGICA
Reactor mixing angle from hybrid neutrino masses
In terms of its eigenvector decomposition, the neutrino mass matrix (in the
basis where the charged lepton mass matrix is diagonal) can be understood as
originating from a tribimaximal dominant structure with small deviations, as
demanded by data. If neutrino masses originate from at least two different
mechanisms, referred to as "hybrid neutrino masses", the experimentally
observed structure naturally emerges provided one mechanism accounts for the
dominant tribimaximal structure while the other is responsible for the
deviations. We demonstrate the feasibility of this picture in a fairly
model-independent way by using lepton-number-violating effective operators,
whose structure we assume becomes dictated by an underlying flavor
symmetry. We show that if a second mechanism is at work, the requirement of
generating a reactor angle within its experimental range always fixes the solar
and atmospheric angles in agreement with data, in contrast to the case where
the deviations are induced by next-to-leading order effective operators. We
prove this idea is viable by constructing an -based ultraviolet
completion, where the dominant tribimaximal structure arises from the type-I
seesaw while the subleading contribution is determined by either type-II or
type-III seesaw driven by a non-trivial singlet (minimal hybrid model).
After finding general criteria, we identify all the symmetries
capable of producing such -based minimal hybrid models.Comment: 18 pages, 5 figures. v3: section including sum rules added, accepted
by JHE
Neutrino masses in with adjoint flavons
We present a supersymmetric model for neutrino masses
and mixings that implements the seesaw mechanism by means of the heavy SU(2)
singlets and triplets states contained in three adjoints of SU(5). We discuss
how Abelian symmetries can naturally yield non-hierarchical light
neutrinos even when the heavy states are strongly hierarchical, and how it can
also ensure that --parity arises as an exact accidental symmetry. By
assigning two flavons that break to the adjoint representation of
SU(5) and assuming universality for all the fundamental couplings, the
coefficients of the effective Yukawa and Majorana mass operators become
calculable in terms of group theoretical quantities. There is a single free
parameter in the model, however, at leading order the structure of the light
neutrinos mass matrix is determined in a parameter independent way.Comment: 16 pages, 9 figures. Included contributions to neutrino masses from
the triplet states contained in the three adjoints of SU(5
Neutrino masses beyond the tree level
Models for Majorana neutrino masses can be classified according to the level
in perturbation theory at which the effective dimension five operator is
realized. The possibilities range from the tree-level up to the three-loop
level realizations. We discuss some general aspects of this approach and
speculate about a model independent classification of the possible cases. Among
all the realizations, those in which the effective operator is induced by
radiative corrections open the possibility for lepton number violation near -or
at- the electroweak scale. We discuss some phenomenological aspects of two
generic radiative realizations: the Babu-Zee model and supersymmetric models
with bilinear R-parity violation.Comment: 7 pages, 3 figures. Contribution to the workshop "30 years of strong
interactions", Spa, Belgium, 6-8 April 201
Minimal lepton flavor violating realizations of minimal seesaw models
We study the implications of the global U(1)R symmetry present in minimal
lepton flavor violating implementations of the seesaw mechanism for neutrino
masses. In the context of minimal type I seesaw scenarios with a slightly
broken U(1)R, we show that, depending on the R-charge assignments, two classes
of generic models can be identified. Models where the right-handed neutrino
masses and the lepton number breaking scale are decoupled, and models where the
parameters that slightly break the U(1)R induce a suppression in the light
neutrino mass matrix. We show that within the first class of models,
contributions of right-handed neutrinos to charged lepton flavor violating
processes are severely suppressed. Within the second class of models we study
the charged lepton flavor violating phenomenology in detail, focusing on mu to
e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable
contributions to these processes are naturally obtained for right-handed
neutrino masses at the TeV scale. We then discuss the interplay with the
effects of the right-handed neutrino interactions on primordial B - L
asymmetries, finding that sizable right-handed neutrino contributions to
charged lepton flavor violating processes are incompatible with the requirement
of generating (or even preserving preexisting) B - L asymmetries consistent
with the observed baryon asymmetry of the Universe.Comment: 21 pages, 4 figures; version 2: Discussion on possible generic models
extended, typos corrected, references added. Version matches publication in
JHE
Phonon assisted dynamical Coulomb blockade in a thin suspended graphite sheet
The differential conductance in a suspended few layered graphene sample is
fou nd to exhibit a series of quasi-periodic sharp dips as a function of bias
at l ow temperature. We show that they can be understood within a simple model
of dyn amical Coulomb blockade where energy exchanges take place between the
charge carriers transmitted trough the sample and a dissipative electromagnetic
envir onment with a resonant phonon mode strongly coupled to the electrons
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