Phenomenological viability of orbifold models with three Higgs families

We discuss the phenomenological viability of string multi-Higgs doublet models, namely a scenario of heterotic $Z_3$ orbifolds with two Wilson lines, which naturally predicts three supersymmetric families of matter and Higgs fields. We study the orbifold parameter space, and discuss the compatibility of the predicted Yukawa couplings with current experimental data. We address the implications of tree-level flavour changing neutral processes in constraining the Higgs sector of the model, finding that viable scenarios can be obtained for a reasonably light Higgs spectrum. We also take into account the tree-level contributions to indirect CP violation, showing that the experimental value of $\epsilon_K$ can be accommodated in the present framework.Comment: 31 pages, 12 figures. Comments and references added. Final version to be published in JHE

Noncommutative QCD, first-order-in-theta-deformed instantons and 't Hooft vertices

For commutative Euclidean time, we study the existence of field configurations that {\it a)} are formal power series expansions in h\theta^{\m\n}, {\it b)} go to ordinary (anti-)instantons as h\theta^{\m\n}\to 0, and {\it c)} render stationary the classical action of Euclidean noncommutative SU(3) Yang-Mills theory. We show that the noncommutative (anti-)self-duality equations have no solutions of this type at any order in h\theta^{\m\n}. However, we obtain all the deformations --called first-order-in-$\theta$-deformed instantons-- of the ordinary instanton that, at first order in h\theta^{\m\n}, satisfy the equations of motion of Euclidean noncommutative SU(3) Yang-Mills theory. We analyze the quantum effects that these field configurations give rise to in noncommutative SU(3) with one, two and three nearly massless flavours and compute the corresponding 't Hooft vertices, also, at first order in h\theta^{\m\n}. Other issues analyzed in this paper are the existence at higher orders in h\theta^{\m\n} of topologically nontrivial solutions of the type mentioned above and the classification of the classical vacua of noncommutative SU(N) Yang-Mills theory that are power series in h\theta^{\m\n}.Comment: Latex. Some macros. No figures. 42 pages. Typos correcte

In vitro exposure of acer negundo pollen to atmospheric levels of SO2 and NO2: effects on allergenicity and germination

In the last years, a rising trend of pollen allergies in urban areas has been attributed to atmospheric pollution. In this work, we investigated the effects of SO2 and NO2 on the protein content, allergenicity, and germination rate of Acer negundo pollen. A novel environmental chamber was assembled to exposure pollen samples with SO2 or NO2 at two different levels: just below and two times the atmospheric hour-limit value acceptable for human health protection in Europe. Results showed that protein content was lower in SO2- exposed pollen samples and slightly higher in NO2-exposed pollen compared to the control sample. No different polypeptide profiles were revealed by SDSPAGE between exposed and nonexposed pollen, but the immunodetection assays indicated higher IgE recognition by all sera of sensitized patients to Acer negundo pollen extracts in all exposed samples in comparison to the nonexposed samples. A decrease in the germination rate of exposed in contrast to nonexposed pollen was verified, which was more pronounced for NO2-exposed samples. Our results indicated that in urban areas, concentrations of SO2 and NO2 below the limits established for human protection can indirectly aggravate pollen allergy on predisposed individuals and affect plant reproduction

Composición química de semillas de cacahuete aborigen (Arachis hypogaea L.) de Uruguay.

Oil, protein, carbohydrate and ash contents, iodine value, and fatty acid and sterol compositions were studied in seed of 9 aboriginal (Arachis hypogaea subsp. fastigiata var. vulgaris cultivars originating from Uruguay. They showed a high protein level as other varieties of the subspecie fastigiata (these protein percentages are higher than varieties of subspecie (hypogaea ). Palmitic (16:0), stearic (18:0), oleic (18:1), linoleic (18:2), arachidic (20:0), eicosenoic (20:1), behenic (22:0), and lignoceric (24:0) acids were detected. The cultivar 7 Uv showed higher oleic acid content (42.53%) and 0/L ratio (1.09). The cultivars 2 Uv and 5 Uv had higher percentage in linoleic acid (43.67% and 43.40%, respectively). The cultivar 3 Uv and 4 Uv exhibited lower iodine value (104.90 and 104.73, respectively). Cholesterol, campesterol, stigmasterol, β-sitosterol, Δ5-avenasterol, Δ7-estigmasteroI and Δ7-avenasterol were detected in the sterols, β-sitosterol was the most abundant. Significant difference was only found for stigmasterol. The chemical quality of these seeds is characterized by higher protein levels and oils with lower O/L ratio and higher iodine value.Se han estudiado los contenidos en aceite, proteína, hidrato de carbono y ceniza, índice de yodo y composición en ácidos grasos y esteroles en semillas de 9 cultivares aborígenes (Arachis hypogaea subsp. fastigiata var. vulgaris originarios de Uruguay. Estos mostraron un nivel alto en proteína como las otras variedades de la subespecie fastigiata (estos porcentajes en proteína son mayores que en las variedades de la subespecie (hypogaea ). Se detectaron los ácidos palmítico (16:0), esteárico (18:0), oleico (18:1), linoleico (18:2), araquídico (20:0), eicosenoico (20:1), behénico (22:0) y lignocérico (24:0). El cultivar 7 Uv mostró el mayor contenido en ácido oleico (42. 53%) y en la relación oleico/linoleico (1.09). Los cultivares 2 Uv y 5 Uv tuvieron los mayores porcentajes en ácido linoleico (43.67% y 43.40%, respectivamente). El cultivar 3 Uv y el 4 Uv exhibieron los más bajos índices de yodo (104.90 y 104.73, respectivamente). En los esteroles se detectaron colesterol, campesterol, estigmasterol, β-sitosterol, Δ5-avenasterol, Δ7-estigmasteroI y Δ7-avenasterol; siendo el β-sitosterol el más abundante. Sólo se encontró diferencias significativas para el estigmasterol. La calidad química de estas semillas se caracterizó por sus mayores niveles en proteína y aceites con la más baja relación oleico/linoleico y los mayores índices de yodo

Calidad del agua en el tramo bajo del Río Negro (Chaco, Argentina)

Las principales características físicas, químicas y biológicas fueron medidas entre noviembre de 1999 y mayo de 2002 en 4 sitios ubicados en el cauce principal del río Negro. En los sitios 1 y 2 los humedales y bosques con baja ocupación humana constituyen el paisaje característico que bordea al curso principal. Los sitios 3 y 4 están afectados por descargas domésticas e industriales, aunque la producción de tanino fue de menor volumen en los últimos años. La composición química del agua superficial estuvo influenciada por la estacionalidad de las lluvias y el lavado de suelos ricos en sales de los humedales hacia el canal del río. La conductividad eléctrica del agua durante las sequías fue más alta que la registrada después de las lluvias. La salinidad fluctuó de manera semejante entre 82,7 mg.l-1 y 6500 mg.l-1. La concentración promedio de fósforo total fue alta (1053 µg.l-1) y el pH neutro o ligeramente alcalino. En el sitio 4, el contenido de materia orgánica (DQO=385 mg.l-1) aumentó significativamente durante el periodo de aguas bajas. No se encontraron residuos de 27 plaguicidas y compuestos organoclorados en los sedimentos del fondo de los sitios muestreados. El contenido de Plomo y Cadmio de los sedimentos estuvo debajo del límite de detección. Los valores de Cromo varió entre 14 y 22 µg.g de sedimento seco, dependiendo del sitio estudiado. Diez especies de plantas acuáticas fueron recolectadas en el Sitio 1 que se caracterizó por baja velocidad de flujo. La riqueza de macrófitas disminuyó aguas abajo. La ocurrencia de algunas especies, tales como Hydrocotyle ranunculoides y Ceratophyllum demersum, estuvo relacionada con la buena disponibilidad de fósforo. La biomasa de algas indicada por la concentración de clorofila a fue baja en todos los sitios estudiados (inferior a 20 µg.l-1)

Dynamical Supersymmetry Breaking in Standard-like Models with Intersecting D6-branes

We address dynamical supersymmetry breaking within a N=1 supersymmetric Standard-like Model based on a Z_2 x Z_2 Type IIA orientifold with intersecting D6-branes. The model possesses an additional, confining gauge sector with the USp(2)_A x USp(2)_B x USp(4) gauge group, where the gaugino condensation mechanism allows for the breaking of supersymmetry and stabilizes moduli. We derive the leading contribution to the non-perturbative effective superpotential and determine numerically the minima of the supergravity potential. These minima break supersymmetry and fix two undetermined moduli, which in turn completely specify the gauge couplings at the string scale. For this specific construction the minima have a negative cosmological constant. We expect that for other supersymmetric Standard-like models with intersecting D6-branes, which also possess confining gauge sectors, the supersymmetry breaking mechanism would have qualitatively similar features.Comment: 19 pages, 1 figur

Neutralino-Nucleon Cross Section and Charge and Colour Breaking Constraints

We compute the neutralino-nucleon cross section in several supersymmetric scenarios, taking into account all kind of constraints. In particular, the constraints that the absence of dangerous charge and colour breaking minima imposes on the parameter space are studied in detail. In addition, the most recent experimental constraints, such as the lower bound on the Higgs mass, the $b\to s\gamma$ branching ratio, and the muon $g-2$ are considered. The astrophysical bounds on the dark matter density are also imposed on the theoretical computation of the relic neutralino density, assuming thermal production. This computation is relevant for the theoretical analysis of the direct detection of dark matter in current experiments. We consider first the supergravity scenario with universal soft terms and GUT scale. In this scenario the charge and colour breaking constraints turn out to be quite important, and \tan\beta\lsim 20 is forbidden. Larger values of $\tan\beta$ can also be forbidden, depending on the value of the trilinear parameter $A$. Finally, we study supergravity scenarios with an intermediate scale, and also with non-universal scalar and gaugino masses where the cross section can be very large.Comment: Final version to appear in JHE

Anomalous U(1) D-term Contribution in Type I String Models

We study the $D$-term contribution for anomalous U(1) symmetries in type I string models and derive general formula for the $D$-term contribution, assuming that the dominant source of SUSY breaking is given by $F$-terms of the dilaton, (overall) moduli or twisted moduli fields. On the basis of the formula, we also point out that there are several different features from the case in heterotic string models. The differences originate from the different forms of K\"ahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models.Comment: 16 pages, latex, no figur

String instantons, fluxes and moduli stabilization

We analyze a class of dual pairs of heterotic and type I models based on freely-acting $\mathbb{Z}_2 \times \mathbb{Z}_2$ orbifolds in four dimensions. Using the adiabatic argument, it is possible to calculate non-perturbative contributions to the gauge coupling threshold corrections on the type I side by exploiting perturbative calculations on the heterotic side, without the drawbacks due to twisted moduli. The instanton effects can then be combined with closed-string fluxes to stabilize most of the moduli fields of the internal manifold, and also the dilaton, in a racetrack realization of the type I model.Comment: 1+49 page