Exotic properties of neutrinos using effective Lagrangians and specific models

En este trabajo doctoral estudiamos algunas propiedades no estándar de los neutrinos a través de las sinergias entre teorías de campos efectivas y modelos. Los fenómenos elegidos son analizados, en una primera etapa, a través de operadores efectivos, lo cual permite estudiar sus consecuencias sin especificar los detalles de su origen y, a la vez, derivar algunas estimaciones sobre la escala de masas de las partículas que serían necesarias para producir los nuevos fenómenos. En una segunda etapa proponemos modelos concretos que dan lugar a esas interacciones efectivas; los modelos contienen más información que la teoría efectiva y nos permiten poner a prueba las conclusiones que habíamos extraído en primera instancia, demostrando que no contenían ambigüedades; además, los modelos también permiten explorar los aspectos del fenómeno en cuestión que quedan fuera del alcance de la teoría efectiva -- aunque, eso sí, las consecuencias que se extraigan en este caso se circunscribirán sólo al modelo considerado, y no al fenómeno en su conjunto. El texto está dividido en dos partes: en la primera aplicamos estas ideas a una interacción efectiva que genera momentos dipolares magnéticos para neutrinos dextrógiros, y en la segunda analizamos una familia de operadores sin quarks que violan el número lepónico y que pueden generar, a la vez, masas de neutrinos pequeñas y tasas altas de desintegración doble beta sin neutrinos. Los momentos magnéticos de neutrinos dextrógiros pueden potencialmente manifestarse en una plétora de diferentes escenarios, y el hecho de que no los hayamos observado permite acotar su valor, y por ende las masas de las nuevas partículas asociadas. Los operadores analizados en la segunda parte del texto tienen potencial para dominar el proceso de desintegración doble beta sin neutrinos y para arrojar señales en diferentes experimentos en el futuro inmediato; estos operadores se pueden clasificar según la quiralidad de los leptones involucrados, y las masas de neutrinos que inducen presentan claras jerarquías relacionadas con los valores de las masas de los leptones cargados. En ambos casos proporcionamos modelos de ejemplo que dan lugar a esta fenomenología, y analizamos su observabilidad en experimentos presentes y planeados para un futuro próximo.This doctoral dissertation presents several works on nonstandard properties of neutrinos exploiting the synergies between effective field theory and models. The phenomena are first analysed by means of effective operators, which allow to discuss their phenomenological consequences and to derive estimations about the mass scale of the heavy particles needed to induce the new interactions. In a second phase we propose models that realise the effective operators, allowing us to check the conclusions of effective field theory as well as to extract new phenomenological features of the scenarios considered. The text is divided into two parts: in the first one we apply these ideas to an effective interaction that generates magnetic dipole moments for right-handed neutrinos, and in the second one we discuss a family of operators that violate lepton number without quarks, and which can allow for large rates of neutrinoless double beta decay and small neutrino masses. The right-handed neutrino magnetic moments have the potential to show up in many different scenarios, and the nonobservation of the associated phenomenology allows to constrain their value, and therefore the associated new physics scale. The operators discussed in the second part of the text can potentially dominate neutrinoless double beta decay and provide signals in the next generation of experiments; they can be classified according to the chirality of the two final-state leptons, and induce neutrino mass matrices with a well-defined hierarchy related to that of the charged lepton masses. In both cases we provide example models that realise the phenomenology and we discuss their observability in ongoing and near-future experiments

A realistic model of neutrino masses with a large neutrinoless double beta decay rate

The minimal Standard Model extension with the Weinberg operator does accommodate the observed neutrino masses and mixing, but predicts a neutrinoless double beta ($0\nu\beta\beta$) decay rate proportional to the effective electron neutrino mass, which can be then arbitrarily small within present experimental limits. However, in general $0\nu\beta\beta$ decay can have an independent origin and be near its present experimental bound; whereas neutrino masses are generated radiatively, contributing negligibly to $0\nu\beta\beta$ decay. We provide a realization of this scenario in a simple, well defined and testable model, with potential LHC effects and calculable neutrino masses, whose two-loop expression we derive exactly. We also discuss the connection of this model to others that have appeared in the literature, and remark on the significant differences that result from various choices of quantum number assignments and symmetry assumptions. In this type of models lepton flavor violating rates are also preferred to be relatively large, at the reach of foreseen experiments. Interestingly enough, in our model this stands for a large third mixing angle, $\sin^2\theta_{13} \gtrsim 0.008$, when $\mu \rightarrow eee$ is required to lie below its present experimental limit.Comment: Published extended version with further reference

Implications of new generations on neutrino masses

We explore the possible implications that new families, that are being searched for at the LHC, would have on neutrino masses. In particular, we have explored the possibility that the smallness of the observed neutrino masses is naturally understood in a modified version of the Standard Model (SM) with complete extra generations of fermions, i.e., that have right-handed neutrinos, in which neutrino masses are generated at two loops. With one extra family it is not possible to fit the observed spectrum of masses and mixings. However, the radiative mass generated provides an important constraint in these kind of models, so the neutrino masses do not exceed their cosmological bound. Within the context of two extra families, we analyse the allowed parameter space and the possible phenomenological signals

Neutrinoless double β decay with small neutrino masses

If the only contribution to neutrinoless double beta decay (0νβ β) are neutrino masses its discovery may be very difficult, especially if neutrinos present a normal hierarchy spectrum. However, this is not the only possibility; 0νβ β can in general produce electrons of either chirality, in contrast with the neutrino induced 0νβ β which predicts two left-handed electrons. Using an effective Lagrangian approach we classify the lepton number violating (LNV) effective operators with two leptons of either chirality but no quarks, ordered according to the magnitude of their contribution to 0νβ β. We point out that, for each of the three chirality assignments, eLeL, eLeR and eReR , there is only one LNV operator of the corresponding type to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino masses are always induced by these extra operators but can be delayed to one (dimension 7) or two loops (dimension 9). Under the assumption that 0νβ β is dominated by the operators of dimension 7 or 9 we find that the scale of new physics should be relatively low (. 30 TeV). We also list the SM additions generating these operators upon integration of the heavy modes, and discuss simple realistic examples of renormalizable theories for each case. The phenomenology of a model giving rise to the dimension 9 operator has been analyzed with some detail: if 0νβ β is going to be seen in the next round of experiments, the doubly charged scalars of the model could be seen at the LHC and lepton flavour violating (LFV) rates could be at the reach of foreseen experiments. Moreover neutrino masses, which arise at two loops, display a very particular structure and are strongly constrained, in fact, sin2 θ13 & 0.008, when µ → eee is required to lie below its present experimental limit

Neutrinoless double β decay with small neutrino masses

Proceedings of the Corfu Summer Institute 2012 "School and Workshops on Elementary Particle Physicsand Gravity", September 8-27, 2012, Corfu (Greece). PoS(Cofu2012)028.If the only contribution to neutrinoless double beta decay (0vββ) are neutrino masses its discovery may be very difficult, especially if neutrinos present a normal hierarchy spectrum. However, this is not the only possibility; 0nbb can in general produce electrons of either chirality, in contrast with the neutrino induced 0vββ which predicts two left-handed electrons. Using an effective Lagrangian approach we classify the lepton number violating (LNV) effective operators with two leptons of either chirality but no quarks, ordered according to the magnitude of their contribution to 0vββ. We point out that, for each of the three chirality assignments, eLeL;eLeR and eReR , there is only one LNV operator of the corresponding type to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino masses are always induced by these extra operators but can be delayed to one (dimension 7) or two loops (dimension 9). Under the assumption that 0nbb is dominated by the operators of dimension 7 or 9 we find that the scale of new physics should be relatively low (< 30 TeV). We also list the SM additions generating these operators upon integration of the heavy modes, and discuss simple realistic examples of renormalizable theories for each case. The phenomenology of a model giving rise to the dimension 9 operator has been analyzed with some detail: if 0vββ is going to be seen in the next round of experiments, the doubly charged scalars of the model could be seen at the LHC and lepton flavour violating (LFV) rates could be at the reach of foreseen experiments. Moreover neutrino masses, which arise at two loops, display a very particular structure and are strongly constrained, in fact, sin2 ϴ13 > 0,008, when μ --> eee is required to lie below its present experimental limit

New rurality and generation of social discourses from the productive sphere: shepherding meanings (Castellón, Spain)

Los espacios rurales resisten en variadas formas a la despoblación y aquellos que allí desarrollan -parcial o totalmente- sus vidas redefinen su posición en unos territorios de intensa movilidad. En este artículo se plantea cómo dicha redefinición ideológica genera discursos que construyen y contrastan el concepto de nueva ruralidad. Se analizan aquí los discursos de una serie de propuestas productivas del espacio rural de Castellón (España) definidas por sus rasgos como nueva ruralidad y que, expuestas en el seno de unas jornadas de reflexión y debate, apuntan hacia ideas emergentes que pueden aportar claves para las políticas de desarrollo rural.Rural spaces resist depopulation in various ways and those who develop, partially or totally, their lives redefine their position in territories of intense mobility. In this article, we propose how this ideological redefinition generates discourses that construct and contrast the concept of new rurality. The discourses of a series of productive proposals of the rural area of Castellón (Spain) are analyzed here, defined by their features as new rurality and that, exposed in a few days of reflection and debate conference, point towards emerging ideas that can contribute keys elements for the policies of rural development

A model for right-handed neutrino magnetic moments

A simple extension of the Standard Model providing Majorana magnetic moments to right-handed neutrinos is presented. The model contains, in addition to the Standard Model particles and right-handed neutrinos, just a singly charged scalar and a vector-like charged fermion. The phenomenology of the model is analysed and its implications in cosmology, astrophysics and lepton flavour violating processes are extracted. If light enough, the charged particles responsible for the right-handed neutrino magnetic moments could copiously be produced at the LHC.Comment: 16 pages, 5 figure

Right-handed neutrino magnetic moments

We discuss the phenomenology of the most general effective Lagrangian, up to operators of dimension 5, build with standard model fields and interactions including right-handed neutrinos. In particular we find there is a dimension 5 electroweak moment operator of right-handed neutrinos, not discussed previously in the literature, which could have interesting phenomenological consequences.Comment: 34 pages, 8 figure

On the nature of the fourth generation neutrino and its implications

We consider the neutrino sector of a Standard Model with four generations. While the three light neutrinos can obtain their masses from a variety of mechanisms with or without new neutral fermions, fourth-generation neutrinos need at least one new relatively light right-handed neutrino. If lepton number is not conserved this neutrino must have a Majorana mass term whose size depends on the underlying mechanism for lepton number violation. Majorana masses for the fourth generation neutrinos induce relative large two-loop contributions to the light neutrino masses which could be even larger than the cosmological bounds. This sets strong limits on the mass parameters and mixings of the fourth generation neutrinos.Comment: To be published. Few typos corrected, references update

Neutrino masses from new generations

We reconsider the possibility that Majorana masses for the three known neutrinos are generated radiatively by the presence of a fourth generation and one right-handed neutrino with Yukawa couplings and a Majorana mass term. We find that the observed light neutrino mass hierarchy is not compatible with low energy universality bounds in this minimal scenario, but all present data can be accommodated with five generations and two right-handed neutrinos. Within this framework, we explore the parameter space regions which are currently allowed and could lead to observable effects in neutrinoless double beta decay, $\mu - e$ conversion in nuclei and $\mu \rightarrow e \gamma$ experiments. We also discuss the detection prospects at LHC.Comment: 28 pages, 4 figures. Version to be published. Some typos corrected. Improved figures 3 and