Some remarks on the observational constraints on the self-interacting scalar field model for dark energy

The dark energy component of the cosmic budget is represented by a self-interacting scalar field. The violation of the null energy condition is allowed. Hence, such component can also represent a phantom fluid. The model is tested using supernova type Ia and matter power spectrum data. The supernova test leads to preferred values for configurations representing the phantom fluid. The matter power spectrum constraints for the dark energy equation of state parameter are highly degenerated. In both cases, values for the equation of state parameter corresponding to the phantom fluid are highly admitted if no particular prior is used.Comment: Latex file, 12 pages, 12 figures in eps forma

Scalar models for the unification of the dark sector

We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity.Comment: Latex file, 8 pages, 3 figures in eps format. To appear in the proceedings of the CosmoSul conference, held in Rio de Janeiro, Brazil, 01-05 august of 201

Duality between k-essence and Rastall gravity

The k-essence theory with a power-law function of $(\partial\phi)^2$ and Rastall's non-conservative theory of gravity with a scalar field are shown to have the same solutions for the metric under the assumption that both the metric and the scalar fields depend on a single coordinate. This equivalence (called k-R duality) holds for static configurations with various symmetries (spherical, plane, cylindrical, etc.) and all homogeneous cosmologies. In the presence of matter, Rastall's theory requires additional assumptions on how the stress-energy tensor non-conservation is distributed between different contributions. Two versions of such non-conservation are considered in the case of isotropic spatially flat cosmological models with a perfect fluid: one (R1) in which there is no coupling between the scalar field and the fluid, and another (R2) in which the fluid separately obeys the usual conservation law. In version R1 it is shown that k-R duality holds not only for the cosmological models themselves but also for their adiabatic perturbations. In version R2, among other results, a particular model is singled out that reproduces the same cosmological expansion history as the standard $\Lambda$CDM model but predicts different behaviors of small fluctuations in the k-essence and Rastall frameworks.Comment: 10 pages, no figures. Two references adde

Bouncing solutions in Rastall's theory with a barotropic fluid

Rastall's theory is a modification of Einstein's theory of gravity where the covariant divergence of the stress-energy tensor is no more vanishing, but proportional to the gradient of the Ricci scalar. The motivation of this theory is to investigate a possible non-minimal coupling of the matter fields to geometry which, being proportional to the curvature scalar, may represent an effective description of quantum gravity effects. Non-conservation of the stress-energy tensor, via Bianchi identities, implies new field equations which have been recently used in a cosmological context, leading to some interesting results. In this paper we adopt Rastall's theory to reproduce some features of the effective Friedmann's equation emerging from loop quantum cosmology. We determine a class of bouncing cosmological solutions and comment about the possibility of employing these models as effective descriptions of the full quantum theory.Comment: Latex file, 14 pages, 1 figure in eps format. Typos corrected, one reference added. Published versio

Inertial-Hall effect: the influence of rotation on the Hall conductivity

Inertial effects play an important role in classical mechanics but have been largely overlooked in quantum mechanics. Nevertheless, the analogy between inertial forces on mass particles and electromagnetic forces on charged particles is not new. In this paper, we consider a rotating non-interacting planar two-dimensional electron gas with a perpendicular uniform magnetic field and investigate the effects of the rotation in the Hall conductiv

On Attitudes Toward Spanish Varieties: A Bilingual Perspective

This study explores the attitudes of 25 English-Spanish bilingual speakers from Tucson (Arizona) towards their own variety and compares them with their attitudes toward monolingual varieties of Mexican (from Hermosillo) and Peninsular Spanish (from Murcia and Madrid). Our analysis points to a clear influence of the standard language ideology (MILROY, 2001) on shaping these attitudes, escalated by a tendency among bilinguals in diglossic societies to feel insecure about their own variety as a minority language, or towards a feeling of linguistic self-hatred. - Este estudo explora as atitudes de 25 falantes bilíngues de espanhol e inglês de Tucson (Arizona) com relação à sua própria variedade linguística, comparando essas atitudes em relação ao espanhol de Hermosillo (México) e a duas variedades peninsulares: a espanhola de Múrcia e a de Madrid. Nossa análise mostra uma clara influência da ideologia da língua padrão (MILROY, 2001) em determinar essas atitudes, agravada pela tendência de os falantes bilíngues de sociedades diglóssicas se sentirem inseguros quanto à sua própria variedade como uma língua minoritária, ou relacionada a um sentimento de auto-ódio linguístico