Effects of quark family nonuniversality in SU(3)_c X SU(4)_L X U(1)_x models

Flavour changing neutral currents arise in the $SU(3)_c\otimes SU(4)_L\otimes U(1)_X$ extension of the standard model because anomaly cancellation among the fermion families requires one generation of quarks to transform differently from the other two under the gauge group. In the weak basis the distinction between quark families is meaningless. However, in the mass eigenstates basis, the Cabibbo-Kobayashi-Maskawa mixing matrix motivates us to classify left-handed quarks in families. In this sense there are, in principle, three different assignments of quark weak eigenstates into mass eigenstates. In this work, by using measurements at the Z-pole, atomic parity violation data and experimental input from neutral meson mixing, we examine two different models without exotic electric charges based on the 3-4-1 symmetry, and address the effects of quark family nonuniversality on the bounds on the mixing angle between two of the neutral currents present in the models and on the mass scales $M_{Z_2}$ and $M_{Z_3}$ of the new neutral gauge bosons predicted by the theory. The heaviest family of quarks must transform differently in order to keep lower bounds on $M_{Z_2}$ and $M_{Z_3}$ as low as possible without violating experimental constraints.Comment: 27 pages, 10 tables, 2 figures. Equation (19) and typos corrected. Matches version to appear in Phys. Rev.

Fertilización de pastos. Cartilla 8

La cartilla describe el concepto de fertilización, las recomendaciones básicas para fertilizar los pastos, elementos nutritivos que requieren las plantas, fertilizantes y aplicación del fertilizanteThe primer describes the concept of fertilization, the basic recommendations for fertilizing pastures, nutritious elements required by plants, fertilizers and application of fertilizerElementos nutritivos requeridos por las plantas – Fertilicemos los pastos – Aplicación del fertilizante33 página

First report of Carybdea xaymacana Conant, 1897 (Cnidaria, Cubozoa, Carybdeida) in Colombia

Carybdea xaymacana Conant, 1897 is a box jellyfish belonging to the family Carybdeidae and is currently recorded from the Mexican Caribbean (State of Quintana Roo), Puerto Rico, the Bahamas, Jamaica, Panama, and Venezuela. Here, we report for the first time the presence of this species in Colombia, based on collections made in three departments of the Colombian Caribbean. Documenting the extension in the distribution range of this species is of great importance due to its ecological role in regional ecosys-tems