11,142 research outputs found
Is U(1) a Good Family Symmetry?
We analyze U(1) as a horizontal symmetry and its possibilities to explain
the known elementary-fermion masses. We find that only two candidates, in the
context of SU(3)SU(2)U(1)U(1)
nonsupersymmetric, are able to fit the experimental result mm.Comment: 10 pages, Accepted for publication in Z. Phys.
Hydrostatic Equilibrium of a Perfect Fluid Sphere with Exterior Higher-Dimensional Schwarzschild Spacetime
We discuss the question of how the number of dimensions of space and time can
influence the equilibrium configurations of stars. We find that dimensionality
does increase the effect of mass but not the contribution of the pressure,
which is the same in any dimension. In the presence of a (positive)
cosmological constant the condition of hydrostatic equilibrium imposes a lower
limit on mass and matter density. We show how this limit depends on the number
of dimensions and suggest that is more effective in 4D than in
higher dimensions. We obtain a general limit for the degree of compactification
(gravitational potential on the boundary) of perfect fluid stars in
-dimensions. We argue that the effects of gravity are stronger in 4D than in
any other number of dimensions. The generality of the results is also
discussed
Walter KERN, René LATOURELLE, Giuseppe GROPPO, Gianni AMBROSIO, Istanze della teologia fondamentale oggi, Bologna, Istituto Trentino di Cultura («Publicazioni dell'Istituto di Scienze Religiose in Trento», 2), 1982, 167 pp., 14 x 22. [RECENSIÓN]
Aurelio FERNÁNDEZ, Nuevas estructuras de la Iglesia. Exigencias teológicas de la Comunión Eclesial, Burgos, Ed. Aldecoa, 1980, 340 pp. 18 X 25. [RECENSIÓN]
Stellar models with Schwarzschild and non-Schwarzschild vacuum exteriors
A striking characteristic of non-Schwarzschild vacuum exteriors is that they
contain not only the total gravitational mass of the source, but also an {\it
arbitrary} constant. In this work, we show that the constants appearing in the
"temporal Schwarzschild", "spatial Schwarzschild" and
"Reissner-Nordstr{\"o}m-like" exteriors are not arbitrary but are completely
determined by star's parameters, like the equation of state and the
gravitational potential. Consequently, in the braneworld scenario the
gravitational field outside of a star is no longer determined by the total mass
alone, but also depends on the details of the internal structure of the source.
We show that the general relativistic upper bound on the gravitational
potential , for perfect fluid stars, is significantly increased in
these exteriors. Namely, , and for the
temporal Schwarzschild, spatial Schwarzschild and Reissner-Nordstr{\"o}m-like
exteriors, respectively. Regarding the surface gravitational redshift, we find
that the general relativistic Schwarzschild exterior as well as the braneworld
spatial Schwarzschild exterior lead to the same upper bound, viz., .
However, when the external spacetime is the temporal Schwarzschild metric or
the Reissner-Nordstr{\"o}m-like exterior there is no such constraint: . This infinite difference in the limiting value of is because for
these exteriors the effective pressure at the surface is negative. The results
of our work are potentially observable and can be used to test the theory.Comment: 19 pages, 3 figures and caption
International briefing 34: training and development in Spain
© 2016 John Wiley & Sons Ltd This article locates training and development in Spain within the country's socio-economic context. It maps the major changes which have been introduced into the training and development system since the briefing by Escardíbul and Llinas-Audet published in this journal in 2010. It relates those changes to the ongoing economic crisis which began in 2009 and the growing emphasis on employers’ demands in the design of the training system. Finally, it identifies the challenges presented to Spanish policy-makers by a number of weaknesses in the current system. The Spanish experience is particularly relevant for countries in which social partner involvement and a significant small and medium-sized enterprise (SME) presence are important issues in the development of their training system. It is also particularly useful for those countries in Latin America whose training systems have been influenced by the Spanish model
Local dynamics for fibered holomorphic transformations
Fibered holomorphic dynamics are skew-product transformations over an
irrational rotation, whose fibers are holomorphic functions. In this paper we
study such a dynamics on a neighborhood of an invariant curve. We obtain some
results analogous to the results in the non fibered case
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