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 $B-L$ 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 $B-L$ asymmetry in a scenario of a concrete $A_4$ flavor model realization.Comment: 25 pages, 7 figures; version 2: A few clarifications added. Version matches publication in JHE

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

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 $A_4$ 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 $A_4$-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 $A_4$ singlet (minimal hybrid model). After finding general criteria, we identify all the $\mathbb{Z}_N$ symmetries capable of producing such $A_4$-based minimal hybrid models.Comment: 18 pages, 5 figures. v3: section including sum rules added, accepted by JHE

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

Muon spin rotation study of magnetism and superconductivity in Ba(Fe1-xCox)2As2 single crystals

Using muon spin rotation (muSR) we investigated the magnetic and superconducting properties of a series of Ba(Fe1-xCox)2As2 single crystals with 0 =< x =< 0.15. Our study details how the antiferromagnetic order is suppressed upon Co substitution and how it coexists with superconductivity. In the non-superconducting samples at 0 < x < 0.04 the antiferromagnetic order parameter is only moderately suppressed. With the onset of superconductivity this suppression becomes faster and it is most rapid between x = 0.045 and 0.05. As was previously demonstrated by muSR at x = 0.055 [P. Marsik et al., Phys. Rev. Lett. 105, 57001 (2010)], the strongly weakened antiferromagnetic order is still a bulk phenomenon that competes with superconductivity. The comparison with neutron diffraction data suggests that the antiferromagnetic order remains commensurate whereas the amplitude exhibits a spatial variation that is likely caused by the randomly distributed Co atoms. A different kind of magnetic order that was also previously identified [C. Bernhard et al., New J. Phys. 11, 055050 (2009)] occurs at 0.055 < x < 0.075 where Tc approaches the maximum value. The magnetic order develops here only in parts of the sample volume and it seems to cooperate with superconductivity since its onset temperature coincides with Tc. Even in the strongly overdoped regime at x = 0.11, where the static magnetic order has disappeared, we find that the low energy spin fluctuations are anomalously enhanced below Tc. These findings point toward a drastic change in the relationship between the magnetic and superconducting orders from a competitive one in the strongly underdoped regime to a constructive one in near optimally and overdoped samples.Comment: 33 Pages, 9 Figure

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 $LLHH$ 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

PRE-NEOGENE DEFORMATION OF THE EASTERN CORDILLERA, AS EVIDENCED BY FORELAND STRATA

&nbsp; Cuatro pulsos de deformación, previo al evento Andino post-Mioceno Medio, se han definido para la Cordillera Oriental a partir de la integración de modelos estratigráficos, de procedencia, estructurales y geodinámicos. Los primeros dos pulsos, de edad Maastrichtiano Tardío y Paleoceno Tardío, fueron definidos por el cambio de patrón de acumulación y procedencia de los sedimentos en la cuenca de antepaís. El tercer pulso de edad Eoceno Temprano-Medio tiene como zona de deformación el flanco occidental de la Cordillera Oriental y el Valle del Magdalena, generando poco espacio de acomodación hacia el este donde se acumularon las formaciones Mirador-Picacho. El cuarto pulso de edad Eoceno tardío-Mioceno Medio se documenta en la zona norte del piedemonte por estratos de crecimientos, en la zona central por el abrupto cambio de espesor de los estratos, y por el inicio de la acumulación en la zona sur de los Llanos. El modelamiento geodinámico permitió establecer tanto la posición de las cargas como su magnitud con respecto al evento de deformación Andino post-Mioceno Medio. Estos cuatro pulsos pre-Mioceno Medio deben considerarse en futuros programas de exploración minera y de hidrocarburos. &nbsp; Palabras clave: cuenca antepaís, Llanos, Cordillera Oriental, historia de levantamiento &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; Strata architecture, provenance, structural and Geodynamic analyses constrain the identification of 4 pulses of deformation,prior to the post-middle Miocene Andean pulse. Change of strata pattern of deposition and provenance in the foreland basin document the first two pulses during the late Maastrichtian-Paleocene time. In the Magdalena Valley and western flank of the Eastern Cordillera concentrated deformation of the third pulse, whereas amalgamated fluvial Mirador- Picacho sandstones accumulated in areas with low-accommodation space patterns. Late Eocene-Middle Miocene strata along the Llanos foothills and Llanos basins record, from north to south, growth strata patterns, abrupt lateral changes of thickness, and diachronous onset of deposition of synorogenic strata. Location of tectonic loads for each pulse was determined based on geodynamic modeling; this approach also allows us to quantify the amount of loading with respect to Andean tectonic loading. These four events of deformation should be considered in future hydrocarbon and mining exploration programs. &nbsp; Keywords: foreland, Llanos, Eastern Cordillera, uplift histor

Relativistic graphene ratchet on semidisk Galton board

Using extensive Monte Carlo simulations we study numerically and analytically a photogalvanic effect, or ratchet, of directed electron transport induced by a microwave radiation on a semidisk Galton board of antidots in graphene. A comparison between usual two-dimensional electron gas (2DEG) and electrons in graphene shows that ratchet currents are comparable at very low temperatures. However, a large mean free path in graphene should allow to have a strong ratchet transport at room temperatures. Also in graphene the ratchet transport emerges even for unpolarized radiation. These properties open promising possibilities for room temperature graphene based sensitive photogalvanic detectors of microwave and terahertz radiation.Comment: 4 pages, 4 figures. Research done at Quantware http://www.quantware.ups-tlse.fr/. More detailed analysis is give

PRE-NEOGENE DEFORMATION OF THE EASTERN CORDILLERA, AS EVIDENCED BY FORELAND STRATA

&nbsp; Cuatro pulsos de deformación, previo al evento Andino post-Mioceno Medio, se han definido para la Cordillera Oriental a partir de la integración de modelos estratigráficos, de procedencia, estructurales y geodinámicos. Los primeros dos pulsos, de edad Maastrichtiano Tardío y Paleoceno Tardío, fueron definidos por el cambio de patrón de acumulación y procedencia de los sedimentos en la cuenca de antepaís. El tercer pulso de edad Eoceno Temprano-Medio tiene como zona de deformación el flanco occidental de la Cordillera Oriental y el Valle del Magdalena, generando poco espacio de acomodación hacia el este donde se acumularon las formaciones Mirador-Picacho. El cuarto pulso de edad Eoceno tardío-Mioceno Medio se documenta en la zona norte del piedemonte por estratos de crecimientos, en la zona central por el abrupto cambio de espesor de los estratos, y por el inicio de la acumulación en la zona sur de los Llanos. El modelamiento geodinámico permitió establecer tanto la posición de las cargas como su magnitud con respecto al evento de deformación Andino post-Mioceno Medio. Estos cuatro pulsos pre-Mioceno Medio deben considerarse en futuros programas de exploración minera y de hidrocarburos. &nbsp; Palabras clave: cuenca antepaís, Llanos, Cordillera Oriental, historia de levantamiento &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; Strata architecture, provenance, structural and Geodynamic analyses constrain the identification of 4 pulses of deformation,prior to the post-middle Miocene Andean pulse. Change of strata pattern of deposition and provenance in the foreland basin document the first two pulses during the late Maastrichtian-Paleocene time. In the Magdalena Valley and western flank of the Eastern Cordillera concentrated deformation of the third pulse, whereas amalgamated fluvial Mirador- Picacho sandstones accumulated in areas with low-accommodation space patterns. Late Eocene-Middle Miocene strata along the Llanos foothills and Llanos basins record, from north to south, growth strata patterns, abrupt lateral changes of thickness, and diachronous onset of deposition of synorogenic strata. Location of tectonic loads for each pulse was determined based on geodynamic modeling; this approach also allows us to quantify the amount of loading with respect to Andean tectonic loading. These four events of deformation should be considered in future hydrocarbon and mining exploration programs. &nbsp; Keywords: foreland, Llanos, Eastern Cordillera, uplift histor