Majorana vs Pseudo-Dirac Neutrinos at the ILC

Neutrino masses could originate in seesaw models testable at colliders, with light mediators and an approximate lepton number symmetry. The minimal model of this type contains two quasi-degenerate Majorana fermions forming a pseudo-Dirac pair. An important question is to what extent future colliders will have sensitivity to the splitting between the Majorana components, since this quantity signals the breaking of lepton number and is connected to the light neutrino masses. We consider the production of these neutral heavy leptons at the ILC, where their displaced decays provide a golden signal: a forward-backward charge asymmetry, which depends crucially on the mass splitting between the two Majorana components. We show that this observable can constrain the mass splitting to values much lower than current bounds from neutrinoless double beta decay and natural loop corrections.Comment: 16 pages, 5 figures; v2: Minor changes, version accepted for publication in EPJ

Social representation of the environment and air pollution: effect of overlap of two objects

International audienceSocial representations are forms of social thought, socially built and therefore with a practical use. In the environmental field, this theory has shown a greater interest in understanding the sociocognitive basis underlying to different behaviors and positions of that object of social interest. This study starts from the hypothesis that different environmental objects (water, air, environmental risks, sustainable development), work as a network of representations for being overlapped or anchored in the environment social representation as a policy framework. 305 people participated in the study, half of an urban population exposed to high levels of of the air pollution (Medellin center = exposed) and the other half living in an area with negative indices of the air pollution (Municipality Girardota= unexposed). Through various analyzes that identify the internal organization of environment and air pollution social representations, we try to empirically show the central role of the "risk" factor in the first one. An effect of exposure to air pollution sources is evidence for the second object (air pollution), specifically in the attribution of causes of pollution.Las representaciones sociales son formas de pensamiento social, socialmente construidas y, en consecuencia, con una utilidad práctica. En el campo ambiental esta teoría ha demostrado un interés mayor en la comprensión de la base sociocognitiva subyacente a diferentes comportamientos y tomas de posición frente a este objeto de interés social. Este estudio parte de la hipótesis de que los diferentes objetos ambientales (agua, aire, riesgos ambientales, desarrollo sostenible), funcionan como una red de representaciones por el hecho de estar imbricados o anclados en la representación social del medio ambiente como marco normativo. 305 personas participaron al estudio, la mitad habitantes de una zona urbana expuesta a altos índices de polución (Medellín centro=expuestos) del aire y la otra mitad habitantes de una zona con índices negativos de polución (Municipio de Girardota=no expuestos). A través de diferentes análisis que buscan hacer hipótesis sobre la organización interna de las representaciones sociales del medio ambiente y de la contaminación del aire, se muestra empíricamente el rol central del componente “riesgo” en la primera. Un efecto de exposición a fuentes de polución del aire se evidencia para el segundo objeto (contaminación del aire), específicamente en la atribución de causas de la misma

Análisis psicosocial de los conflictos de uso del agua: percepciones y atribuciones entre categorías de usuarios de un mismo recurso

International audienceThis study aimed at exploring the perceptions, evaluations and attributions regarding water usage in a context of tension and conflict between different categories of users of the same river basin. To this end, 201 people who use one basin originating in the northern slope of the Sierra Nevada de Santa Marta (SNSM) were interviewed. The interviewees belonged to different sociocultural categories: Colombian natives, city dwellers, and peasants. Four points were assessed: attributions of the causes of water misuse, estimation of the amount of water used, types of perceived and/or attributed uses for water and judgements regarding water usage among the groups of users. It is concluded that tension exists between users living in the city and those living in the countryside. The former are considered to be responsible for misusing and contaminating water. This evaluation is essentially based on the types of use perceived. We confirmed the initial hypothesis that is based on the influence of the living environment in social representations, perceptions, and judgments about an environmental object and on the intergroup relationships of those who share a territory and its resources.El presente estudio buscaba explorar las percepciones, las evaluaciones y las atribuciones en relación al uso del agua en un contexto de tensión y conflicto entre diferentes categorías de usuarios de una misma cuenca. Para ello se entrevistaron 201 personas usuarios de la misma cuenca proveniente de la vertiente norte de la Sierra Nevada de Santa Marta (SNSM), diferenciados por pertenecer a diferentes categorías socioculturales y territoriales: Urbanos y rurales (Indígenas y campesinos. Se evaluaron cuatro aspectos: Atribución de causas del mal uso del agua, estimación de la cantidad de agua utilizada, tipos de usos del agua percibidos y/o atribuidos y los juicios sobre el uso del agua entre grupos de usuarios. Se concluye que existe una tensión entre los usuarios que habitan en zona urbana con los habitantes de zona rural, los primeros considerados responsables de malos usos y contaminación del recurso. La base de esta valoración son fundamentalmente los tipos de uso percibidos. Se confirma la hipótesis de partida que se basa en la influencia que tiene el entorno de vida en las representaciones sociales, las percepciones y los juicios sobre un objeto medioambiental así como en las relaciones intergrupales de quienes comparten un territorio y sus recursos

Dark matter as a dynamic effect due to a non-minimal gravitational coupling with matter

In this work the phenomenology of models possessing a non-minimal coupling between matter and geometry is discussed, with a particular focus on the possibility of describing the flattening of the galactic rotation curves as a dynamically generated effect derived from this modification to General Relativity. Two possibilities are discussed: firstly, that the observed discrepancy between the measured rotation velocity and the classical prediction is due to a deviation from geodesic motion, due to a non-(covariant) conservation of the energy-momentum tensor; secondly, that even if the principle of energy conservation holds, the dynamical effects arising due to the non-trivial terms in the Einstein equations of motion can give rise to an extra density contribution that may be interpreted as dark matter. The mechanism of the latter alternative is detailed, and a numerical session ascertaining the order of magnitude of the relevant parameters is undertaken, with possible cosmological implications discussed.Comment: Talk given at First Mediterranean Conference on Classical and Quantum Gravity, Kolymbari, Greece, 14-18 September 2009