Asymmetric tri-bi-maximal mixing and residual symmetries

Asymmetric tri-bi-maximal mixing is a recently proposed, grand unified theory (GUT) based, flavor mixing scheme. In it, the charged lepton mixing is fixed by the GUT connection to down-type quarks and a $\mathcal{T}_{13}$ flavor symmetry, while neutrino mixing is assumed to be tri-bi-maximal (TBM) with one additional free phase. Here we show that this additional free phase can be fixed by the residual flavor and CP symmetries of the effective neutrino mass matrix. We discuss how those residual symmetries can be unified with $\mathcal{T}_{13}$ and identify the smallest possible unified flavor symmetries, namely $(\mathbb{Z}_{13}\times\mathbb{Z}_{13})\rtimes \mathrm{D}_{12}$ and $(\mathbb{Z}_{13}\times\mathbb{Z}_{13})\rtimes \mathrm{S}_4$. Sharp predictions are obtained for lepton mixing angles, CP violating phases and neutrinoless double beta decay.Comment: 16 pages, 7 figures, 2 table

CP Violation from Flavor Symmetry in a Lepton Quarticity Dark Matter Model

We propose a simple $\Delta (27) \otimes Z_4$ model where neutrinos are predicted to be Dirac fermions. The smallness of their masses follows from a type-I seesaw mechanism and the leptonic CP violating phase correlates with the pattern of $\Delta (27)$ flavor symmetry breaking. The scheme naturally harbors a WIMP dark matter candidate associated to the Dirac nature of neutrinos, in that the same $Z_4$ lepton number symmetry also ensures dark matter stability.Comment: 16 pages, 5 figures, Dark Matter Direct Detection Constraints Updated, Conclusions Unchanged, Published Versio

Generalized Bottom-Tau unification, neutrino oscillations and dark matter: predictions from a lepton quarticity flavor approach

We propose an $A_4$ extension of the Standard Model with a Lepton Quarticity symmetry correlating dark matter stability with the Dirac nature of neutrinos. The flavor symmetry predicts (i) a generalized bottom-tau mass relation involving all families, (ii) small neutrino masses are induced a la seesaw, (iii) CP must be significantly violated in neutrino oscillations, (iv) the atmospheric angle $\theta_{23}$ lies in the second octant, and (v) only the normal neutrino mass ordering is realized.Comment: 13 pages, 3 figure

Seesaw roadmap to neutrino mass and dark matter

We describe the many pathways to generate Majorana and Dirac neutrino mass through generalized dimension-5 operators a la Weinberg. The presence of new scalars beyond the Standard Model Higgs doublet implies new possible field contractions, which are required in the case of Dirac neutrinos. We also notice that, in the Dirac neutrino case, the extra symmetries needed to ensure the Dirac nature of neutrinos can also be made responsible for stability of dark matter.Comment: 12 pages, 5 figures, published versio

Theory and phenomenology of Dirac neutrinos: Symmetry breaking patterns, flavour implications and Dark Matter

El Modelo Estándar (SM en ingles) de interacciones Electro-Débiles (EW en inglés) ha sido un gran éxito desde un punto de vista teórico y experimental. Si bien este éxito no se puede negar, es hora de avanzar y abordar las preguntas que el SM deja sin respuesta, como las masas de neutrinos, la naturaleza de la materia oscura, el problema de la jerarquía o el problema de violación de CP en el sector de las interacciones fuertes, entre otros. De hecho, el SM predice neutrinos sin masa. Sin embargo, los experimentos de oscilación de neutrinos, que ahora alcanzan la era de la precisión, muestran claramente que al menos dos neutrinos son masivos y arrojan luz sobre su patrón de mezcla. Sin embargo, las oscilaciones de neutrinos no pueden profundizar en las cuestiones más profundas de la naturaleza de los neutrinos: ¿cuál es la escala absoluta de las masas de neutrinos? ¿Su naturaleza es Dirac o Majorana? Se necesitan observaciones complementarias para responder a estas preguntas con experimentos presentes y futuros. Desde el punto de vista teórico, el SM debe ampliarse para incluir masas de neutrinos. La forma más sencilla de hacerlo es agregar el compañero diestro del campo de neutrinos. Entonces, si no se amplía el inventario de simetría del SM, se viola el número leptónico en dos unidades y los neutrinos resultan ser Majorana. Este es el llamado mecanismo de balancín tipo I, que explica elegantemente las masas de neutrinos y su pequeñez. Se han desarrollado muchos mecanismos de masas diferentes, incluidas múltiples variantes de balancín, así como modelos radiativos. Sin embargo, la comunidad generalmente asume que los neutrinos son campos de Majorana, y la opción de Dirac ha sido relativamente poco estudiada. En esta tesis nos centramos en la posibilidad de que los neutrinos sean partículas de Dirac. Comenzamos dando una definición general de un fermión de Dirac y los requisitos de simetría para tener neutrinos de Dirac. En este sentido, el patrón de ruptura del número leptónico es un concepto central para determinar si los neutrinos serán campos de Dirac. Sin embargo, tenga en cuenta que la naturaleza Dirac de los neutrinos se puede proteger con simetrías distintas del número leptónico, incluso no abelianas. Esta simetría puede desempeñar al mismo tiempo diferentes roles: puede ser la simetría PQ, estabilizar la materia oscura, explicar la jerarquía de masa de fermiones del SM, etc. Luego procedemos a revisar el zoológico del balancín de Dirac. Estos son mecanismos elegantes que pueden explicar naturalmente la pequeñez de las masas de neutrinos. Algunos de ellos son de gran escala, pero otros, como los balancines inversos o dobles, pueden tener mediadores de escala TeV y fenomenología observable. Alternativamente, la pequeñez de las masas de neutrinos puede explicarse por su origen radiativo si se generan a través de bucles cuánticos. Es en este marco que la conexión de la simetría BL con la oscuridad se vuelve más clara: puede al mismo tiempo estabilizar la materia oscura, que corre en el bucle de masa de neutrinos, proteger la Diracness de neutrinos y explicar la pequeñez de los neutrinos al prohibir el término de masa a nivel de árbol, también. como calibrado y libre de anomalías. Finalmente, mostramos dos modelos de ejemplo que presentan neutrinos de Dirac y fenomenología comprobable en predicciones de sabor para procesos de oscilación y LFV.The Standard Model (SM) of Electro-Weak (EW) interactions has been a tremendous success from a theoretical and experimental point of view. While this success cannot be denied, it is time to move forward and address the questions that the SM leaves unanswered, such as neutrino masses, the nature of dark matter, the hierarchy problem or the strong CP problem among others. Indeed, the SM predicts massless neutrinos. However, neutrino oscillation experiments, now reaching the precision era, clearly show that at least two neutrinos are massive and shed light into their mixing pattern. However, neutrino oscillations cannot delve into the deeper questions of neutrino nature: what is the absolute scale of neutrino masses? Is their nature Dirac or Majorana? Complementary observations are needed to answer these questions with present and future experiments. From the theoretical point of view, the SM must be extended to include neutrino masses. The most straightforward way of doing so is adding the right-handed partner of the neutrino field. Then, if the symmetry inventory of the SM is not extended, lepton number is violated in two units and neutrinos turn out to be Majorana. This is the so-called seesaw mechanism type I, which elegantly explains neutrino masses and their smallness. Many different mass mechanisms have been developed, including multiple seesaw variants as well as radiative models. However, the community usually assumes that neutrinos are Majorana fields, and the Dirac option has been relatively understudied. In this thesis we focus on the possibility that neutrinos are Dirac particles. We start by giving a general definition of a Dirac fermion and the symmetry requirements to have Dirac neutrinos. In this sense, the lepton number breaking pattern is a central concept to determine whether neutrinos will be Dirac fields. Note however that neutrino Diracness can be enforced with symmetries other than lepton number, even non-abelian. This symmetry can at the same time play different roles: it can be the PQ symmetry, stabilize dark matter, explain the fermion mass hierarchy of the SM etc. Then we proceed to review the Dirac seesaw zoo. These are elegant mechanisms which can naturally explain the smallness of neutrino masses. Some of them are high scale, but others, like the inverse or double seesaws, can have TeV scale mediators and observable phenomenology. Alternatively, the smallness of neutrino masses can be explained by their radiative origin if they are generated via quantum loops. It is in this framework that the B-L symmetry connection with dark becomes clearer: it can at the same time stabilize dark matter, which runs in the neutrino mass loop, protect neutrino Diracness and explain neutrino smallness by forbidding the tree level mass term, as well as being gauged and anomaly free. Finally, we show two example models which feature Dirac neutrinos and testable phenomenology in flavour predictions for oscillation and LFV processes

CDF-II W boson mass in the Dirac Scotogenic model

The Dirac scotogenic model provides an elegant mechanism which explains small Dirac neutrino masses and neutrino mixing, with a single symmetry simultaneously protecting the ``Diracness'' of the neutrinos and the stability of the dark matter candidate. Here we explore the phenomenological implications of the recent CDF-II measurement of the $W$ boson mass in the Dirac scotogenic framework. We show that, in the scenario where the dark matter is mainly a $SU(2)_L$ scalar doublet, it cannot concurrently satisfy: (a) the dark matter relic density (b) the $m_W$ anomaly and (c) the direct detection constraints. However, unlike the Majorana scotogenic model, the Dirac version also has a ``dark sector'' $SU(2)_L$ singlet scalar. We show that if the singlet scalar is the lightest dark sector particle i.e. the dark matter, then all neutrino physics and dark matter constraints along with the constraints from oblique $S$, $T$ and $U$ parameters can be concurrently satisfied for $W$ boson mass in CDF-II mass range.Comment: 18 pages, 10 figures, 2 tables. Updated to match published versio

Dirac Neutrinos and Dark Matter Stability from Lepton Quarticity

We propose to relate dark matter stability to the possible Dirac nature of neutrinos. The idea is illustrated in a simple scheme where small Dirac neutrino masses arise from a type--I seesaw mechanism as a result of a $Z_4$ discrete lepton number symmetry. The latter implies the existence of a viable WIMP dark matter candidate, whose stability arises from the same symmetry which ensures the Diracness of neutrinos.Comment: 12 pages, 6 figures, Report N IFIC/16-4

CP Symmetries as Guiding Posts: revamping tri-bi-maximal Mixing. Part II

In this follow up of arXiv:1812.04663 we analyze the generalized CP symmetries of the charged lepton mass matrix compatible with the complex version of the Tri-Bi-Maximal (TBM) lepton mixing pattern. These symmetries are used to `revamp' the simplest TBM \textit{Ansatz} in a systematic way. Our generalized patterns share some of the attractive features of the original TBM matrix and are consistent with current oscillation experiments. We also discuss their phenomenological implications both for upcoming neutrino oscillation and neutrinoless double beta decay experiments.Comment: 19 pages, 8 figures. Title change to match the first par