Cosmological constant constraints from observation-derived energy condition bounds and their application to bimetric massive gravity

Among the various possibilities to probe the theory behind the recent accelerated expansion of the universe, the energy conditions (ECs) are of particular interest, since it is possible to confront and constrain the many models, including different theories of gravity, with observational data. In this context, we use the ECs to probe any alternative theory whose extra term acts as a cosmological constant. For this purpose, we apply a model-independent approach to reconstruct the recent expansion of the universe. Using Type Ia supernova, baryon acoustic oscillations and cosmic-chronometer data, we perform a Markov Chain Monte Carlo analysis to put constraints on the effective cosmological constant $\Omega^0_{\rm eff}$. By imposing that the cosmological constant is the only component that possibly violates the ECs, we derive lower and upper bounds for its value. For instance, we obtain that $0.59 < \Omega^0_{\rm eff} < 0.91$ and $0.40 < \Omega^0_{\rm eff} < 0.93$ within, respectively, $1\sigma$ and $3\sigma$ confidence levels. In addition, about 30\% of the posterior distribution is incompatible with a cosmological constant, showing that this method can potentially rule it out as a mechanism for the accelerated expansion. We also study the consequence of these constraints for two particular formulations of the bimetric massive gravity. Namely, we consider the Visser's theory and the Hassan and Roses's massive gravity by choosing a background metric such that both theories mimic General Relativity with a cosmological constant. Using the $\Omega^0_{\rm eff}$ observational bounds along with the upper bounds on the graviton mass we obtain constraints on the parameter spaces of both theories.Comment: 11 pages, 4 figures, 1 tabl

Potencial de sequestro do carbono em solo pela incorporação de carvão das cascas de frutos da castanha-do-Brasil.

Utilizou-se um ensaio de respirometria para estimar o potencial de sequestro de carbono no solo pela incorporação de carvão das cascas de frutos da castanha-do-brasil. Os carvões produzidos a 350ºC, 450ºC e 550°C foram adicionados ao solo contendo microorganismos e paralelamente em meio abiótico, cujos frascos foram vedados para quantificação da evolução do carvão em CO2. O ensaio foi monitorado por 182 dias verificando-se taxas decrescentes de CO2, cujas curvas apresentaram formato logarítmico. Observou-se que no processo abiótico a formação de CO2 é superior quando comparada ao processo biótico, e que o carvão produzido a 550°C apresenta maior taxa de mineralização que os demais carvões. Além disso, verifica-se que todas as amostras de carvão possuem estabilidade no solo a longo prazo

The conservation of energy-momentum and the mass for the graviton

In this work we give special attention to the bimetric theory of gravitation with massive gravitons proposed by Visser in 1998. In his theory, a prior background metric is necessary to take in account the massive term. Although in the great part of the astrophysical studies the Minkowski metric is the best choice to the background metric, it is not possible to consider this metric in cosmology. In order to keep the Minkowski metric as background in this case, we suggest an interpretation of the energy-momentum conservation in Visser's theory, which is in accordance with the equivalence principle and recovers naturally the special relativity in the absence of gravitational sources. Although we do not present a general proof of our hypothesis we show its validity in the simple case of a plane and dust-dominated universe, in which the `massive term' appears like an extra contribution for the energy density.Comment: 9 pages, accepted for publishing in GR

Extra polarization states of cosmological gravitational waves in alternative theories of gravity

Cosmological Gravitational Waves (GWs) are usually associated with the transverse-traceless part of the metric perturbations in the context of the theory of cosmological perturbations. These modes are just the usual polarizations `+' and `x' which appear in the general relativity theory. However, in the majority of the alternative theories of gravity, GWs can present more than these two polarization states. In this context, the Newman-Penrose formalism is particularly suitable for evaluating the number of non-null GW modes. In the present work we intend to take into account these extra polarization states for cosmological GWs in alternative theories of gravity. As an application, we derive the dynamical equations for cosmological GWs for two specific theories, namely, a general scalar-tensor theory which presents four polarization states and a massive bimetric theory which is in the most general case with six polarization states for GWs. The mathematical tool presented here is quite general, so it can be used to study cosmological perturbations in all metric theories of gravity.Comment: 26 pages, 1 figure. Accepted for publication in Classical and Quantum Gravity

Diversidade de espécies de aves em silvicultura de eucalipto.

Com a rápida e crescente expansão da silvicultura, especialmente no Estado de São Paulo, é comum o debate sobre os impactos e possíveis benefícios de tal prática, principalmente sobre a biodiversidade. Entretanto, levantamentos de indicadores de biodiversidade nessas áreas ainda são escassos e existe uma grande lacuna de conhecimento. Este trabalho apresenta resultados sobre a caracterização da avifauna encontrada em uma propriedade de silvicultura de Eucalyptus no Município de Brotas, SP. A amostragem da avifauna foi realizada usando a metodologia de contagem por pontos. Após seis campanhas de campo foram registradas 53 espécies de aves para a área de estudo, distribuídas em 23 famílias e 11 ordens. A ordem dos Passeriformes foi a que apresentou maior número de espécies (34) e de contatos (132). De acordo com a análise da frequência de ocorrência, poucas espécies mostraram-se frequentes na região e outras apareceram em um único ponto, fato que poderia ser indicativo de grande variedade de nichos ecológicos. Análises futuras avaliarão a diversidade da fauna em relação a indicadores de ecologia da paisagem e em relação à fitossociologia do sub-bosque nas áreas de cultivo de eucalipto.bitstream/item/56791/1/015-11.pd

Saturation of Cs2 Photoassociation in an Optical Dipole Trap

We present studies of strong coupling in single-photon photoassociation of cesium dimers using an optical dipole trap. A thermodynamic model of the trap depletion dynamics is employed to extract absolute rate coefficents. From the dependence of the rate coefficient on the photoassociation laser intensity, we observe saturation of the photoassociation scattering probability at the unitarity limit in quantitative agreement with the theoretical model by Bohn and Julienne [Phys. Rev. A, 60, 414 (1999)]. Also the corresponding power broadening of the resonance width is measured. We could not observe an intensity dependent light shift in contrast to findings for lithium and rubidium, which is attributed to the absence of a p or d-wave shape resonance in cesium