1,763 research outputs found
Dark Energy in vector-tensor theories of gravity
We consider a general class of vector-tensor theories of gravity and show
that solutions with accelerated expansion and a future type III singularity are
a common feature in these models. We also show that there are only six
vector-tensor theories with the same small scales behavior as General
Relativity and, in addition, only two of them can be made completely free from
instabilities. Finally, two particular models as candidates for dark energy are
proposed: on one hand, a cosmic vector that allows to alleviate the usual
naturalness and coincidence problems and, on the other hand, the
electromagnetic field is shown to give rise to an effective cosmological
constant on large scales whose value can be explained in terms of inflation at
the electroweak scale.Comment: 4 pages, 1 table. Contribution to the proceedings of Spanish
Relativity Meeting 2009, Bilbao, Spain, 7-11 September 200
Invariant Sylow subgroups and solvability of finite groups
Let A and G be finite groups of relatively prime orders and
assume that A acts on G via automorphisms. We study how certain conditions
on G imply its solvability when we assume the existence of a
unique A-invariant Sylow p-subgroup for p equal to 2 or 3.This research is supported by Universitat Jaume I, Grant P11B2012-05, and by the Valencian Government, Proyecto PROMETEOII/2015/011
Iconografía numástica: retratos de los barkidas en las monedas cartaginesas de plata de Cartagena
Invariant complements normalized by the fixed point subgroup
Abstract. Let A and G be finite groups and assume that A acts on G by automorphisms with (|A|, |G|) = 1. Let CG(A) be the fixed point subgroup and fix a prime
number p. We prove that if G possesses an A-invariant p-complement that is normalized
by CG(A), then G is p-solvable. We also extend Frobenius criterion for p-nilpotency, in
the coprime action setting, for the primes 2 and 3
A cosmic vector for dark energy
In this work we show that the presence of a vector field on cosmological
scales could explain the present phase of accelerated expansion of the
universe. The proposed theory contains no dimensional parameters nor potential
terms and does not require unnatural initial conditions in the early universe,
thus avoiding the so called cosmic coincidence problem. In addition, it fits
the data from high-redshift supernovae with excellent precision, making
definite predictions for cosmological parameters. Upcoming observations will be
able to clearly discriminate this model from standard cosmology with
cosmological constant.Comment: 5 pages, 3 figures, 1 table. New comments and references included.
Final version to appear in Phys. Rev.
HYDROGEN-BONDED SUPRAMOLECULAR ARRAY IN THE CRYSTAL STRUCTURE OF ETHYL 7-HYDROXY-2-OXO-2H-CHROMENE-3-CARBOXYLATE MONOHYDRATE
Indexación: Web of Science; ScieloThe crystal structure of ethyl 7-hydroxy-2-oxo-2H-chromene-3-carboxylate monohydrate (1), C12H10O5.H2O, was established by X-ray crystallographic analysis. The molecule of the title compound is essentially planar except for the carboxylate substituent group. The crystal packing supramolecular array arises from hydrogen bonds and intermolecular C-H - O=C contacts of the organic molecules and solvent water molecules, with graph-set descriptor R24 (8), R21 (6), R44 ( 20) and C (5) motifs. The water molecules are involved as donors and acceptors. The hydrogen bond and intermolecular interaction network is reinforced by stacking of the sheet through p-p interactions.http://ref.scielo.org/qhfkn
Galileu i el telescopi. Saber i veure
Galileo and the Telescope. Knowing and Seeing.The astronomical discoveries made by Galileo using the telescope transformed astronomy. Galileo presented them as clear evidence of the Copernican theory. However, proponents of traditional Christianized cosmology attacked him from all sides, especially theologians. The Church condemned the theory and the Jesuits, obedient to their superiors, undertook the task of providing theoretical legitimacy, a task which persists even today
El ara romana del Museo de Barcelona y su relación con el culto de la salud y Esculapio en Carthago Nova
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