Reproducing lepton mixing in a texture zero model

We note that the emerging features of lepton mixing can be reproduced if, with inverted neutrino mass ordering, both the smallest neutrino mass and the $\tau\tau$ element of the neutrino mass matrix vanish. Then, the atmospheric neutrino mixing angle is less than maximal and the Dirac phase $\delta$ is close to $\pi$. We derive the correlations among the mixing parameters and show that there is a large cancellation in the effective mass responsible for neutrinoless $\beta\beta$ decay. Three simple seesaw models leading to our scenario are provided.Comment: 11 pages, 4 figure

Unitarity constraints on large multiplets of arbitrary gauge groups

We impose partial-wave unitarity on $2 \to 2$ tree-level scattering processes to derive constraints on the dimensions of large scalar and fermionic multiplets of arbitrary gauge groups. We apply our results to scalar and fermionic extensions of the Standard Model, and also to the Grand Unified Theories (GUTs) based on the groups $SU(5)$, $SO(10)$, and $E_6$. We find scenarios within the latter two GUTs that violate the unitarity condition; this may require a reevaluation of the validity of perturbation theory in those scenarios.Comment: 29 pages, 4 figures, 10 table

The ZbbˉZ b \bar b vertex in a left-right model

We consider the one-loop corrections to the $Z b \bar b$ vertex in a $CP$-conserving left--right model (LRM), $viz$. a model with gauge group $SU(2)_L \times SU(2)_R \times U(1)$. We allow the gauge coupling constants of $SU(2)_L$ and $SU(2)_R$ to be different. The spontaneous symmetry breaking is accomplished only by doublets and/or singlets of $SU(2)_L$ and $SU(2)_R$. The lightest massive neutral gauge boson of our LRM is assumed to have the same Yukawa couplings to bottom-quark pairs as the $Z$ of the Standard Model (SM); this assumption has the advantage that, then, the infrared divergences automatically cancel down in the subtraction of the $Z b \bar b$ vertex in the SM from the same vertex in the LRM. We effect a proper renormalization of the $Z b \bar b$ vertex and check explicitly both its gauge invariance and the cancellation of all the ultraviolet divergences. We find out that a LRM with the above assumptions cannot achieve a better fit to the $Z b \bar b$ vertex than a multi-Higgs extension of the SM, $viz$. both models can only achieve a decent fit when one admits scalar particles with very low masses $\lesssim 50$ GeV. This is true even when we allow for markedly different gauge coupling constants of $SU(2)_L$ and $SU(2)_R$.Comment: 57 pages, 8 figures; v2: added section 3, figure 2 and three references; v3: matches published versio

Oblique corrections from triplet quarks

We present general formulas for the oblique-correction parameters $S$, $T$, $U$, $V$, $W$, and $X$ in an extension of the Standard Model having arbitrary numbers of singlet, doublet, and triplet quarks with electric charges $-4/3$, $-1/3$, $2/3$, and $5/3$ that mix with the standard quarks of the same charge.Comment: 30 page

Zeros of the inverted neutrino mass matrix

I investigate viable textures with two texture zeros for the inverted neutrino mass matrix, and present the predictions of those textures for the neutrino masses and for lepton mixing. By using an Abelian symmetry and one or two heavy scalar singlets, I construct realizations of those textures in the context of seesaw models.Comment: 7 pages, LaTe

Estabelecimento in vitro, caracterização fitoquímica e bioatividade de extratos de Tuberaria lignosa

As plantas medicinais são um recurso cada vez mais procurado em diversas indústrias devido às suas propriedades antioxidantes, antimicrobianas e anti-inflamatórias. A Tuberaria lignosa (tradicionalmente conhecida como Erva Loba) é uma planta medicinal da família Cistaceae, rasteira e de flor amarela e está muito presente em pinhais e zonas áridas, nas regiões do Nordeste Português. As folhas da Tuberaria lignosa são uma fonte de compostos fenólicos, elagitaninos, flavonoides, açúcares e ácido ascórbico. Tem também uma ação inibitória da transcriptase reversa do HIV-1. A micropropagação de plantas é um processo importante para produzir plantas de interesse sem implicações ambientais. Desta forma é importante interligar métodos de análise de propriedades de interesse em plantas com a sua produção e comercialização de forma ininterrupta, rentável, sanificada e sem colocar em causa a extinção de espécies. Neste trabalho foram efetuadas sete tipos de extrações a partir de folhas frescas de Tuberaria lignosa (hidrodestilação, infusão, decocção, metanol 100%, etanol 96%, etanol 50% e n-Hexano) e uma a partir das flores (hidrodestilação), para posteriores testes antioxidantes (DPPH, Poder Redutor), Capacidade Redutora Total e antimicrobianos (difusão em disco e determinação dos valores da concentração mínima inibitória). Paralelamente foi iniciado um ensaio de multiplicação in vitro, pioneiro para esta espécie. Em conclusão, os extratos de Tuberaria lignosa demonstram ter propriedades interessantes sob o ponto de vista de atividade antioxidante, tendo as extrações aquosas demonstrado melhores resultados nos testes realizados. A nível antimicrobiano, o extrato da hidrodestilação das folhas apresenta um valor de MIC de 0.0195 mg/mL para a Candida albicans ATCC 90028 e para a Candida tropicalis ATCC 750, o que revela uma ligeira atividade sobre estas leveduras. O ensaio de multiplicação demonstrou que a luz LED tem uma forte influência no crescimento dos explantes e multiplicação da Tuberaria lignosa.Medicinal plants are a resource increasingly sought in various industries due to its antioxidant, antimicrobial and anti-inflammatory properties. Tuberaria lignosa (traditionally known as Erva Loba) is a medicinal ground plant of the family Cistaceae presenting yellow flower, which is often present in pine forests and arid zones in the regions of Northeast of Portugal. Tuberaria lignosa leaves are a source of phenolic compounds, elagitanins, flavonoids, sugars and ascorbic acid. It also presents an inhibitory action on HIV-1 reverse transcriptase. Micropropagation of plants is an important process to produce plants of interest without environmental implications. In this way, it is important to interconnect methods of analysis of properties of interest in plants with their production in an uninterrupted, profitable and sanitized way, together with the prevention of the extinction of species. In this work, seven types of extractions were performed from fresh leaves of Tuberaria lignosa (hydrodistillation, infusion, decoction, 100% methanol, 96% ethanol, 50% ethanol and n-Hexane) and one from flowers (hydrodistillation) to perform antioxidant tests (DPPH, Reduction Power), Total Reducing Capacity and antimicrobial activity evaluation (disk diffusion and determination of minimum inhibitory concentration). In parallel, a pioneering in vitro multiplication assay was started for this species. In conclusion, Tuberaria lignosa showed interesting antioxidant properties, with aqueous extracts showing better results in the tests performed. Regarding the antimicrobial tests, leaves hydrodistillation extract has a MIC value of 0.0195 mg/mL for Candida albicans ATCC 90028 and for Candida tropicalis ATCC 750, which reveals a slight activity on these yeasts. The multiplication test demonstrated that LED light has a strong influence on explant growth and multiplication of Tuberaria lignosa

A model realizing the Harrison-Perkins-Scott lepton mixing matrix

We present a supersymmetric model in which the lepton mixing matrix $U$ obeys, at the seesaw scale, the Harrison--Perkins--Scott \textit{Ansatz}--vanishing $U_{e3}$, maximal atmospheric neutrino mixing, and $\sin^2{\theta_\odot} = 1/3$ ($\theta_\odot$ is the solar mixing angle). The model features a permutation symmetry $S_3$ among the three lepton multiplets of each type--left-handed doublets, right-handed charged leptons, and right-handed neutrinos--and among three Higgs doublets and three zero-hypercharge scalar singlets; a fourth right-handed neutrino, a fourth Higgs doublet, and a fourth scalar singlet are invariant under $S_3$. In addition, the model has seven \mathbbm{Z}_2 symmetries, out of which six do not commute with $S_3$. Supersymmetry is needed in order to eliminate some quartic terms from the scalar potential, quartic terms which would make impossible to obtain the required vacuum expectation values of the three Higgs doublets and three scalar singlets. The Yukawa couplings to the charged leptons are flavour diagonal, so that flavour-changing neutral Yukawa interactions only arise at loop level.Comment: 16 pages, plain LaTeX, no figures; some clarifying remarks in the conclusions and references added, version accepted for publication in JHE

S3 x Z2 model for neutrino mass matrices

We propose a model for lepton mass matrices based on the seesaw mechanism, a complex scalar gauge singlet and a horizontal symmetry S_3 \times \mathbbm{Z}_2. In a suitable weak basis, the charged-lepton mass matrix and the neutrino Dirac mass matrix are diagonal, but the vacuum expectation value of the scalar gauge singlet renders the Majorana mass matrix of the right-handed neutrinos non-diagonal, thereby generating lepton mixing. When the symmetry $S_3$ is not broken in the scalar potential, the effective light-neutrino Majorana mass matrix enjoys $\mu$--$\tau$ interchange symmetry, thus predicting maximal atmospheric neutrino mixing together with $U_{e3} = 0$. A partial and less predictive form of $\mu$--$\tau$ interchange symmetry is obtained when the symmetry $S_3$ is softly broken in the scalar potential. Enlarging the symmetry group S_3 \times \mathbbm{Z}_2 by an additional discrete electron-number symmetry \mathbbm{Z}_2^{(e)}, a more predicitive model is obtained, which is in practice indistinguishable from a previous one based on the group $D_4$.Comment: 13 pages, 3 figures, final version for publication in JHE

Maximal atmospheric neutrino mixing and the small ratio of muon to tau mass

We discuss the problem of the small ratio of muon mass to tau mass in a class of seesaw models where maximal atmospheric neutrino mixing is enforced through a $\mu$--$\tau$ interchange symmetry. We introduce into those models an additional symmetry $T$ such that $m_\mu = 0$ in the case of exact $T$ invariance. The symmetry $T$ may be softly broken in the Higgs potential, and one thus achieves $m_\mu \ll m_\tau$ in a technically natural way. We speculate on a wider applicability of this mechanism.Comment: 10 pages, plain LaTeX, no figures, minor changes, final version for J. Phys.