The present neutrino oscillation data are compatible with tri-bimaximal mixing, to leading order. The addition of an A₄ family symmetry and extended Higgs sector to the Standard Model can generate this mixing pattern, assuming the correct vacuum expectation value alignment of Higgs scalars. The effect of deviating this alignment is studied, for different types of A₄ models, with a phenomenological emphasis: the effect of perturbations on the model predictions for the neutrino oscillation and neutrino mass observables. The standard theoretical description of neutrino oscillations is presented, along with a summary of the past, present and future experimental efforts aimed at measuring the neutrino mixing parameters. Additionally, the current constraints on the sum of absolute neutrino masses and the amplitude for neutrinoless double beta decay, which is yet to be observed, are discussed. These constraints provide a model-independent test of family symmetery models. The Standard Model is reviewed, and extensions to the Standard Model such as the seesaw mechanism(s) are discussed: these are designed to endow neutrinos with mass, and can be incorporated into A₄ symmetry models. Models with different A₄ particle assignments are analysed for deviations from tribimaximal mixing. There are nine models presented in Chapter 5, with lepton doublets transforming as 3 (underlined) and right-handed charged leptons transforming as 1, 1', 1" (all underlined) ; five of these include right-handed neutrinos transforming as 3 (underlined) and make use of the seesaw mechanism. Chapter 6 contains the analysis of six models that assign all leptons to the 3 (underlined) representation, with four of these utilising the seesaw mechanism. The models are tested for any degree of fine tuning of the parameters that define the mass matrices. The effect of perturbations on the mixing angle observables, in particular sin² ∅₁₃ and sin² ∅₂₃, is studied, as well as the effect on the Jarlskog invariant, Jcp. Investigations of the (Mee)- ∑Mv parameter space allow for comparison with current data, and can lead to the possible exclusion of a particular model by constraints from future data.

The neon-sodium cycle (NeNa cycle) of hydrogen burning is active in stars of the Asymptotic Giant Branch, in classical novae, and in supernovae of type Ia. The thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction is determined by a large number of resonances, and it represents the most uncertain rate in the NeNa cycle. This PhD thesis reports on an experiment to study tentative 22Ne(p,γ)23Na resonances at Elab = 71 and 105 keV, as well as the direct capture component of the reaction rate for Elab ≤ 400 keV. The measurements were performed deep underground at the Laboratory for Un- derground Nuclear Astrophysics - LUNA (Gran Sasso, Italy), taking advantage of the strong reduction in the cosmic ray induced background. The LUNA-400-kV electrostatic accelerator and a differentially pumped, windowless gas target of iso- topically enriched 22Ne gas were used. The γ-rays from the reaction were detected with a 4π bismuth germanate scintillator. The data show upper limits on the strengths of the resonances at Elab = 71 and 105 keV of 5.8 × 10−11 and 7.0 × 10−11 eV respectively. The resonances at Elab = 156.2, 189.5 and 259.7 keV have been re-studied and show 20% higher strength than the literature. The present experiment did not show any evidence for the direct capture process at the low energies studied. In addition to the experimental work at LUNA, the 3He(α, γ)7Be and 7Be(p, γ)8B reactions were studied using the most recent solar neutrino data available. Based on the standard solar model and the experimentally measured fluxes of solar 7Be and 8B neutrinos, the astrophysical S-factors of both reactions were evaluated directly in the solar Gamow peak.

The anomalous Low Energy Excess (LEE) of electron neutrinos and antineutrinos in MiniBooNE has inspired both theories and entire experiments to probe the heart of its mystery. One such experiment is MicroBooNE. This dissertation presents an important facet of its LEE investigation: how a powerful systematic can be levied on this signal through parallel study of a highly correlated channel in muon neutrinos. This constraint serves to strengthen MicroBooNE's ability to confirm or validate the cause of the LEE and will lay the groundwork for future oscillation experiments in Liquid Argon Time Projection Chamber (LArTPC) detector experiments like SBN and DUNE. In addition, this muon channel can be used to test oscillations directly, demonstrated through the world's first muon neutrino disappearance search with LArTPC data.

No description available.

No description available.

While the standard model is enormously successful and internally self consistent, it does not explain a great number of phenomena and is far from a complete theory of particle interactions. Among these missing pieces are a particle theory of dark matter and the Strong CP problem in Quantum Chromodynamics (QCD). A hypothetical axion-like particle (ALP) is a prospective solution to both problems and can be searched for at accelerator produced beam dump experiments. Neutrino detectors can be used for such a search, due to the similar energy regimes and interactions channels of such detections. The Coherent CAPTAIN Mills (CCM) experiment at the Los Alamos Neutron Science Center (LANCSE) has carried out a search for these ALPs across a number of theoretical models, including dark sector variants and the light QCD axion. An initial run with 120 photomultiplier tubes (PMTs) was used to identify 95\% confidence limits placed across parameter space using an engineering run, which identified several paths to improvement for a longer term search to probe the majority of theoretically motivated parameter space.

Una serie de experimentos con neutrinos ha establecido que estos tienen masa, existiendo una mezcla entre sus autoestados de sabor. La mezcla genera una oscilación entre estos autoestados durante la propagación de los neutrinos, descrita por una serie de parámetros y por la diferencia cuadrada de las masas. La propuesta con mayor sensibilidad en la medición de los parámetros de oscilación radica en futuras instalaciones llamadas "fábricas de neutrinos". Estas producirán un alto flujo de neutrinos a partir del decaimiento del muón, siendo capaces de medir una gran variedad de canales de oscilación.

In this thesis, we focus on analyzing the different ways in which new physics scenarios, such as Violation of the Equivalence Principle (VEP) and Quantum Decoherence, can manifest themselves in the context of the neutrino oscillation phenomenon. Within the framework of the DUNE experiment, we examine several effects of the VEP, such as the possibility of getting a misconstructed neutrino oscillation parameter region provoked by our ignorance of VEP in nature, as well as the impact on the DUNE sensitivity for CPV and mass hierarchy. Additionally, we set limits for the different textures of the gravitational matrix and the diverse scenarios of energy dependencies associated with the Lorentz Violation. On the other hand, we demonstrate that the quantum decoherence phenomenon applied to the neutrino system leads us to fascinating phenomenological scenarios. One of the scenarios analyzed, within the context of quantum decoherence, is the one that breaks the fundamental CPT symmetry. For the latter, we identify what textures that include certain nondiagonal elements of the decoherence matrix are necessary. In this line, we propose a way to measure the CPT violation in the DUNE experiment using the muon neutrino and antineutrino channels for different energy dependencies. Another intriguing effect of considering the neutrino as an open quantum system is the possibility of discovering the neutrino nature by measuring the Majorana phase at the DUNE experiment achieving a competitive precision. As a consequence of the latter, we find that the crucial measurement of the CP violation phase (δCP), planned to be performed at the DUNE experiment, can be spoiled by the introduction of the decoherence and the Majorana phases in nature. Thus, a signature of a non-null Majorana phase is a sizable distortion in the measurement of the Dirac CP violation phase δCP at DUNE when compared with T2HK measurement. Subsequently, via simulation, we measured the Majorana phase for values of ϕ1/π = ±0.5 and decoherence parameter Γ = 4.5(5.5) × 10−24GeV, reaching a precision of 23 (21) %. This precision is consistent with the corresponding to the Dirac CP phase at T2K experiment. / En la presente tesis, nos enfocamos en analizar las diferentes formas en que los escenarios de física nueva, como la Violación del Principio de Equivalencia (VEP) y la Decoherencia Cuántica, pueden manifestarse en el contexto del fenómeno de oscilación de neutrinos. En el marco del experimento DUNE, examinamos distintos efectos de VEP, como la posibilidad de obtener una región de parámetros de oscilación de neutrinos mal construida debido a no considerar VEP en la naturaleza, el impacto en la sensitividad del experimento DUNE para CPV y la determinación de la jerarquía de masas. Adicionalmente, establecemos límites para las diferentes texturas de la matriz gravitacional y los diversos escenarios con distintas dependencias energéticas asociadas a la Violación de Lorentz. Por otro lado, demostramos que el fenómeno de la decoherencia cuántica aplicado al sistema de neutrinos nos conduce a fascinantes escenarios fenomenológicos. Uno de los escenarios analizados, dentro del contexto de la decoherencia cuántica, es el de la ruptura de la simetría fundamental CPT. Para esto último, identificamos que son necesarias texturas que incluyan ciertos elementos no diagonales de la matriz de decoherencia. En esta línea, proponemos una forma de medir la violación de CPT en el experimento DUNE utilizando los canales de neutrinos y antineutrinos muónicos para diferentes dependencias energéticas. Otro efecto interesante de considerar al neutrino como un sistema cuántico abierto es la posibilidad de descubrir la naturaleza del neutrino midiendo la fase de Majorana en el experimento DUNE con una precisión competitiva. Como consecuencia de lo último, encontramos que la medición de la fase de violación de CP (δCP), planificada para realizarse en el experimento DUNE, puede verse afectada por la introducción de la decoherencia y las fases de Majorana en la naturaleza. Por lo tanto, en el marco de la decoherencia, mostramos que una señal de una fase de Majorana no nula, es la observación de una distorsión considerable en la medición de la fase de violación CP δCP en DUNE en comparación con la medición realizada por T2HK. Posteriormente, mediante simulación, medimos la fase Majorana para valores de ϕ1/π = ±0.5 y el parámetro de decoherencia Γ = 4.5(5.5) × 10−24GeV, alcanzando una precisión de 23 (21) %. Esta precisión es consistente con la medida correspondiente a la fase CP de Dirac en el experimento T2K.

En general, se sabe que una gran variedad de sistemas abiertos pueden ser descritos como subsistemas en interacción con un sistema más grande, llamado ambiente o entorno [1]-[4]. El entorno suele ser considerado un sistema mucho más grande, prácticamente imperturbable ante las interacciones con el sistema abierto, por lo cual, es tomado como invariante en el tiempo. Esto concentra el interés, exclusivamente, en la evolución del subsistema abierto o también llamado reducido. El sistema total, suma del subsistema reducido y entorno, se considera que es un sistema aislado que sigue las reglas usuales de la mecánica cuántica, es decir, realiza una evolución unitaria que conserva la probabilidad. Sin embargo, la evolución del subsistema abierto, sin el entorno, ya no es unitaria, porque al existir interacción con el otro subsistema se desarrollan efectos de dispersión e irreversibilidad. Cuando no hay una correlación inicial entre el subsistema, el entorno y sus interacciones se la considera débil y puede ser descrita en términos de los llamados semigrupos dinámicos cuánticos. Estos son mapeos de la evolución en el tiempo que encierran requerimientos físicos generales como: incremento en la entropía, la composición del tiempo (propiedad de los semigrupos) y positividad completa. La descripción de sistemas abiertos originalmente fue desarrollada para sistemas ópticos-cuánticos. Sin embargo, en este trabajo, nos serviremos de esta teoría para estudiar efectos de decoherencia, en el marco de partículas elementales.

The discovery of neutrino mixing provides the possibility of a non vanishing CP violating phase in the neutrino mixing matrix. CP violation in the leptonic sector can be large enough to explain the matter-antimatter asymmetry in the universe. An indirect probe of CP violation is the experimental measurement of Electric Dipole Moment (EDM). CP violation has been discovered in the quark sector,but it contributes to lepton EDM at the 3-loop level. Neutrino masses can be generated in the standard model via the see-saw mechanism where heavy right-handed neutrinos mix with the weak-basis states. The Majorana nature of the seesaw type neutrinos generates new 2-loop diagrams that lead to a non-vanishing lepton EDM. Only estimates of the resulting EDM have been done in the literature. A full calculation of the 2-loop diagrams and the exact result is presented. / Ph. D.