Observational constraints on late-time Lambda(t) cosmology

The cosmological constant, i.e., the energy density stored in the true vacuum state of all existing fields in the Universe, is the simplest and the most natural possibility to describe the current cosmic acceleration. However, despite its observational successes, such a possibility exacerbates the well known cosmological constant problem, requiring a natural explanation for its small, but nonzero, value. In this paper we study cosmological consequences of a scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter. We test the viability of this scenario and study a possible way to distinguish it from the current standard cosmological model by using recent observations of type Ia supernova (Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic oscillation from the Sloan Digital Sky Survey and the position of the first peak of the cosmic microwave background angular spectrum from the three-year Wilkinson Microwave Anisotropy Probe.Comment: Some important revisions. To appear in Physical Review

Active galactic nuclei, gravitational redshifts, and cosmological tensions

Gravitational redshift is a classical effect of Einstein's General Relativity, already measured in stars, quasars and clusters of galaxies. We here identify the signature of gravitational redshift in the emission lines of active galaxies due to supermassive black holes and discuss their impact on cosmological inference from type Ia supernovae. Firstly, from the full width at half maximum of $H_{\beta}$ lines of 75 Seyfert type I galaxies of the AGN Black Hole Mass Database, we derive a gravitational redshift $z_g = (2.4 \pm 0.9) \times 10^{-4}$. Expanding this analysis to 86755 quasars from DR14 of SDSS we have a mean value $z_g \approx 2.7 \times 10^{-4}$. Then, by comparing the redshifts of 34 lines measured at the central and outer regions of LINER galaxies in the SAMI survey we obtain $z_g = (0.68 \pm 0.09) \times 10^{-4}$. These numbers are compatible with central black holes of $\approx 10^9$ solar masses and broad line regions of $\approx 1$~pc. For non-AGN galaxies the gravitational redshift is compatible with zero and, as they constitute most of SNe Ia host galaxies, the impact on the cosmological parameters is negligible.Comment: 5 pages, 5 figure

Inhomogeneous vacuum energy

Vacuum energy remains the simplest model of dark energy which could drive the accelerated expansion of the Universe without necessarily introducing any new degrees of freedom. Inhomogeneous vacuum energy is necessarily interacting in general relativity. Although the four-velocity of vacuum energy is undefined, an interacting vacuum has an energy transfer and the vacuum energy defines a particular foliation of spacetime with spatially homogeneous vacuum energy in cosmological solutions. It is possible to give a consistent description of vacuum dynamics and in particular the relativistic equations of motion for inhomogeneous perturbations given a covariant prescription for the vacuum energy, or equivalently the energy transfer four-vector, and we construct gauge-invariant vacuum perturbations. We show that any dark energy cosmology can be decomposed into an interacting vacuum+matter cosmology whose inhomogeneous perturbations obey simple first-order equations.Comment: 8 pages; v2 clarified discussion of Chaplygin gas model, references adde

Evolution of density perturbations in decaying vacuum cosmology

We study cosmological perturbations in the context of an interacting dark energy model, in which the cosmological term decays linearly with the Hubble parameter, with concomitant matter production. A previous joint analysis of the redshift-distance relation for type Ia supernovas, baryonic acoustic oscillations, and the position of the first peak in the anisotropy spectrum of the cosmic microwave background has led to acceptable values for the cosmological parameters. Here we present our analysis of small perturbations, under the assumption that the cosmological term, and therefore the matter production, are strictly homogeneous. Such a homogeneous production tends to dilute the matter contrast, leading to a late-time suppression in the power spectrum. Nevertheless, an excellent agreement with the observational data can be achieved by using a higher matter density as compared to the concordance value previously obtained. This may indicate that our hypothesis of homogeneous matter production must be relaxed by allowing perturbations in the interacting cosmological term.Comment: Revised version. To appear in Physical Review

Supernova constraints on decaying vacuum cosmology

There is mounting observational evidence that the expansion of our Universe is undergoing a late-time acceleration. Among many proposals to describe this phenomenon, the cosmological constant seems to be the simplest and the most natural explanation. However, despite its observational successes, such a possibility exacerbates the well known cosmological constant problem, requiring a natural explanation for its small, but nonzero, value. In this paper we consider a cosmological scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter. We show that this model is indistinguishable from the standard one in that the early radiation phase is followed by a long dust-dominated era, and only recently the varying cosmological term becomes dominant, accelerating the cosmic expansion. In order to test the viability of this scenario we have used the most recent type Ia supernova data, i.e., the High-Z SN Search (HZS) Team and the Supernova Legacy Survey (SNLS) Collaboration data. In particular, for the SNLS sample we have found the present matter density and Hubble parameters in the intervals [0.27, 0.37] and [0.68, 0.72], respectively (at 95% c.l.), which is in good agreement with the currently accepted estimates for these parameters.Comment: Version accepted for publication in Physical Review

Observational tests for \Lambda(t)CDM cosmology

We investigate the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat \Lambda CDM case, there is only one free parameter to be adjusted by the data in this class of \Lambda(t)CDM scenarios, namely, the matter density parameter. To perform our analysis we use three of the most recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and the position of the first acoustic peak of the CMB power spectrum. We show that in terms of $\chi^2$ statistics both models provide good fits to the data and similar results. A quantitative analysis discussing the differences in parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2) is studied using the current SDSS and Constitution SNe Ia compilations. A matter power spectrum analysis using the 2dFGRS is also performed, providing a very good concordance with the constraints from the SDSS and Constitution MLCS2k2 data.Comment: Revised version, to appear in JCA

Adaptation of life-cycle inventories of sawn timber used in the structure of roofs in the state of São Paulo

Este trabalho teve como objetivo desenvolver o inventário de ciclo de vida para madeira empregada na estrutura de telhado de edificações populares do Estado de São Paulo, com base na adaptação de inventários existentes na base de dados ecoinvent (versão 3.1) para a realidade da produção madeireira no Brasil. Considerou-se como sistema de produto a produção de 1m3 de madeira serrada de cambará proveniente de manejo florestal sustentável na Amazônia, desde a extração das toras até a peça de madeira serrada estocada em São Paulo. As informações nacionais foram obtidas da literatura. A despeito das semelhanças entre o sistema de produto da base ecoinvent e a realidade nacional na extração das toras na floresta, há diferenças referentes ao transporte até a serraria, ao desdobro das toras e à geração e destinação de resíduos: no Brasil, todas as etapas são executadas próximas à região de exploração, resultando em alterações no modelo de transporte, máquinas empregadas e resíduos gerados. Além disso, os valores de consumo de diesel e eletricidade apresentaram ordens de grandeza diferentes dos ICVs de referência. Com base nessa análise, conclui-se que a estrutura de dados dos ICVs existentes na base ecoinvent auxilia a construção de inventários nacionais e que a adaptação dos inventários é imprescindível para a realização de estudos de avaliação do ciclo de vida condizentes com as condições do Brasil. Entretanto, considerando as diferenças observadas, é recomendada a apuração dos índices de consumo nacionais por meio de verificação e coleta de dados inloc