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

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

Cantos de bodega

En número dedicado a: Zaragoz

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