Density Perturbations in the Brans-Dicke Theory

We analyse the fate of density perturbation in the Brans-Dicke Theory, giving a general classification of the solutions of the perturbed equations when the scale factor of the background evolves as a power law. We study with details the cases of vacuum, inflation, radiation and incoherent matter. We find, for the a negative Brans-Dicke parameter, a significant amplification of perturbations.Comment: 26 pages, latex fil

wd=−1w_d=-1 in interacting quintessence model

A model consisting of quintessence scalar field interacting with cold dark matter is considered. Conditions required to reach $w_d=-1$ are discussed. It is shown that depending on the potential considered for the quintessence, reaching the phantom divide line puts some constraints on the interaction between dark energy and dark matter. This also may determine the ratio of dark matter to dark energy density at $w_d=-1$.Comment: 10 pages, references updated, some notes added, minor changes applied, accepted for publication in Eur. Phys. J.

Angular Conditions,Relations between Breit and Light-Front Frames, and Subleading Power Corrections

We analyze the current matrix elements in the general collinear (Breit) frames and find the relation between the ordinary (or canonical) helicity amplitudes and the light-front helicity amplitudes. Using the conservation of angular momentum, we derive a general angular condition which should be satisfied by the light-front helicity amplitudes for any spin system. In addition, we obtain the light-front parity and time-reversal relations for the light-front helicity amplitudes. Applying these relations to the spin-1 form factor analysis, we note that the general angular condition relating the five helicity amplitudes is reduced to the usual angular condition relating the four helicity amplitudes due to the light-front time-reversal condition. We make some comments on the consequences of the angular condition for the analysis of the high-$Q^2$ deuteron electromagnetic form factors, and we further apply the general angular condition to the electromagnetic transition between spin-1/2 and spin-3/2 systems and find a relation useful for the analysis of the N-$\Delta$ transition form factors. We also discuss the scaling law and the subleading power corrections in the Breit and light-front frames.Comment: 24 pages,2 figure

Influência de diferentes sistemas de uso e manejo na coesão, resistência ao cisalhamento e óxidos de Fe, Si E Al em solo de tabuleiro costeiro de Alagoas Influence of different use and management systems on cohesion, shear strength and Fe, Si and Al oxides in coastal tableland soils of Alagoas state, Brazil

A tensão de cisalhamento e a coesão do solo constituem importantes propriedades físicas do solo, podendo ser influenciadas pelo sistema de manejo e óxidos de Fe, Si e Al do solo. Os efeitos de diferentes sistemas de manejo de solo cultivado com cana-de-açúcar na tensão de cisalhamento, ângulo de atrito interno, coesão do solo e nos teores de óxidos de Fe, Si e Al de um Argissolo Amarelo Coeso foram estudados em quatro áreas da Usina Triunfo, no Estado de Alagoas. Os tratamentos abrangeram: uma área irrigada, uma área não irrigada, uma com aplicação de vinhaça e uma sob floresta nativa, como condição original. Amostras foram tiradas de cada área a 0,2-0,4 m e 0,4-0,8 m de profundidade. Os sistemas sequeiro e irrigado promoveram os maiores aumentos na coesão, ângulo de atrito interno e resistência ao cisalhamento do solo. Os teores de água e de óxidos no solo influíram nos valores de coesão do solo, tendo sido os maiores valores deste atributo obtidos em solos com teores de água mais baixos e solos com maiores teores de óxidos.<br>The shear tension and soil cohesion are important soil physical properties. They are affected by management systems and the content of Fe, Si and Al oxides in the soil. The effects of different sugarcane management systems on the shear tension, angle of internal friction, soil cohesion, and the contents of Fe, Si and Al oxides in a Cohesive Yellow Argisol were studied in four areas of the Triunfo mill in Alagoas State, Brazil. The treatments consisted of an area cultivated with irrigation and another without irrigation, a site with vinasse application. A native forest area was included as reference for the original conditions. Samples were collected from each site at depths of 0.2-0.4 m and 0.4-0.8 m. The areas cultivated with and without irrigation promoted the greatest increase in soil cohesion, angle of internal friction and soil shear strength. The water and oxide contents affected the soil cohesion; the highest soil cohesion values were obtained in soils with the lowest water and the highest oxide contents