New Cosmic Accelerating Scenario without Dark Energy

We propose an alternative, nonsingular, cosmic scenario based on gravitationally induced particle production. The model is an attempt to evade the coincidence and cosmological constant problems of the standard model ($\Lambda$CDM) and also to connect the early and late time accelerating stages of the Universe. Our space-time emerges from a pure initial de Sitter stage thereby providing a natural solution to the horizon problem. Subsequently, due to an instability provoked by the production of massless particles, the Universe evolves smoothly to the standard radiation dominated era thereby ending the production of radiation as required by the conformal invariance. Next, the radiation becomes sub-dominant with the Universe entering in the cold dark matter dominated era. Finally, the negative pressure associated with the creation of cold dark matter (CCDM model) particles accelerates the expansion and drives the Universe to a final de Sitter stage. The late time cosmic expansion history of the CCDM model is exactly like in the standard $\Lambda$CDM model, however, there is no dark energy. This complete scenario is fully determined by two extreme energy densities, or equivalently, the associated de Sitter Hubble scales connected by $\rho_I/\rho_f=(H_I/H_f)^{2} \sim 10^{122}$, a result that has no correlation with the cosmological constant problem. We also study the linear growth of matter perturbations at the final accelerating stage. It is found that the CCDM growth index can be written as a function of the $\Lambda$ growth index, $\gamma_{\Lambda} \simeq 6/11$. In this framework, we also compare the observed growth rate of clustering with that predicted by the current CCDM model. Performing a $\chi^{2}$ statistical test we show that the CCDM model provides growth rates that match sufficiently well with the observed growth rate of structure.Comment: 12 pages, 3 figures, accepted for publication by Phys. Rev. D. (final version, some references have corrected). arXiv admin note: substantial text overlap with arXiv:1106.193

Analysing and controlling the tax evasion dynamics via majority-vote model

Within the context of agent-based Monte-Carlo simulations, we study the well-known majority-vote model (MVM) with noise applied to tax evasion on simple square lattices, Voronoi-Delaunay random lattices, Barabasi-Albert networks, and Erd\"os-R\'enyi random graphs. In the order to analyse and to control the fluctuations for tax evasion in the economics model proposed by Zaklan, MVM is applied in the neighborhod of the noise critical $q_{c}$. The Zaklan model had been studied recently using the equilibrium Ising model. Here we show that the Zaklan model is robust and can be reproduced also through the nonequilibrium MVM on various topologies.Comment: 18 pages, 7 figures, LAWNP'09, 200

Impacts of a specific soil database on streamflow simulation with SWAT in an experimental rural catchment of the Brazilian savanna.

This study aimed to evaluate the impacts of using a specific soil database on streamflow simulation with SWAT model in an experimental rural catchment of the Brazilian savana (Cerrado biome). In order to accomplish that, two soil databases were tested, one generated by data measured in the studied area (Sim1), and the other from literature (Sim2). The Upper Jardim Experimental River Basin (105 km2), located in a rural zone of the Brazilian Federal District, due to this remarkable soil database, was chosen as the study area. Streamflow simulations were performed for two consecutive years (2006-2008), on a daily basis. No calibration was performed to make it possible to analyze the impact of the soil database on the first simulation, what is relevant mainly for ungagged basins. Even having better physical basis, the results obtained by Sim1 (NSE = -10.81) was worse than the ones generated by Sim2 (NSE = -6.15). The negative NSE values indicate that both simulations failed to represent observed data. Analyzing the hydrographs, it is noticed that: (i) both simulations underestimated baseflow during the dry season; (ii) both simulations overestimated streamflow peaks, but Sim1 presented higher (worst) values; (iii) during the rainy season, the baseflow simulation of Sim1 was satisfactory, while it was overestimated in Sim2. The results reinforce that the model is sensible to soil information, but it shows that it is still necessary more studies about other SWAT parameters, as the ones that control runoff generation

Constraints on Cold Dark Matter Accelerating Cosmologies and Cluster Formation

We discuss the properties of homogeneous and isotropic flat cosmologies in which the present accelerating stage is powered only by the gravitationally induced creation of cold dark matter (CCDM) particles ($\Omega_{m}=1$). For some matter creation rates proposed in the literature, we show that the main cosmological functions such as the scale factor of the universe, the Hubble expansion rate, the growth factor and the cluster formation rate are analytically defined. The best CCDM scenario has only one free parameter and our joint analysis involving BAO + CMB + SNe Ia data yields ${\tilde{\Omega}}_{m}= 0.28\pm 0.01$ ($1\sigma$) where $\tilde{{\Omega}}_{m}$ is the observed matter density parameter. In particular, this implies that the model has no dark energy but the part of the matter that is effectively clustering is in good agreement with the latest determinations from large scale structure. The growth of perturbation and the formation of galaxy clusters in such scenarios are also investigated. Despite the fact that both scenarios may share the same Hubble expansion, we find that matter creation cosmologies predict stronger small scale dynamics which implies a faster growth rate of perturbations with respect to the usual $\Lambda$CDM cosmology. Such results point to the possibility of a crucial observational test confronting CCDM with $\Lambda$CDM scenarios trough a more detailed analysis involving CMB, weak lensing, as well as the large scale structure.Comment: 12 pages, 3 figures, Accepted for publication by Physical Rev.

Hydrological modelling in representative catchments in Brazil using the SWAT model: the experience of the REHIDRO network.

Experimental and numerical studies in Experimental and Representative Basins are essential for water resources planning and for hydrological processes analysis due to land use changes and climate change scenarios. This work presents comparative analysis among diferente catchments in the Brazilian semiarid, and the Cerrado Biome. The Hydrological Network REHIDRO funded by the Brazilian Government (FINEP) has been focused on developing joint hydrological studies, involving the Federal Rural University of Pernambuco State (UFRPE), the Federal University of Pernambuco State (UFPE), the University of Brasília (UnB), and the Brazilian Corporation for Agricultural Research (EMBRAPA Cerrados). Numerical simulation analysis will be discussed, applying the SWAT model for three representative catchments: The Tapacurá Representative Catchment has been studied by UFPE. It is one of the main sub- catchments that supply the Recife Metropolitan Region, northeastern Brazil. The Tapacurá catchment covers an area of about 470 km2. Monitoring and modeling studies have been carried out on stream flow data from January 1997, using the data from a gauging station. The results show that the most sensitive hydrological parameters are the base flow, time of concentration and soil evaporation, which affect the catchment hydrology. The Ipanema catchment is part of the São Francisco River basin, and it is located in the Brazilian drought polygon. The São Francisco Basin has an area representing 8% of Brazilian territory. Na representative (Mimoso) catchment has been monitored as part of the network by the UFRPE, in the Pernambuco State. The study area of UnB research Group is part of the contribution área of the Descoberto reservoir. The Descoberto reservoir is responsible for 63% of the urban water supply of the Brazilian Federal District. The Descoberto reservoir basin has an area of about 420 km2 and the main tributary river has an area of about 114 km2. Flow, rainfall, sediments and nutrient loads has been collected at the main tributary rivers. Six sub-basins have been investigated and monitored, with areas ranging from 16 km2 to 114 km2. The Upper Jardim Experimental River Basin covers an area of about 105 km2, and is located in a rural zone of the Federal District, Brazil, in the core region of the Cerrado biome (Brazilian savanna). Since 2001, in order to generate a database to support hydrological studies in a typical rural catchment of the Brazilian savanna, EMBRAPA Cerrados (Savannas Agricultural Research Center), in partnership with the University of Brasilia (UNB), and other institutions, has intensively characterized and monitored this area. Comparative hydrology is discussed, mainly addressing SWAT parameters sensitivity analysis

A higher quantum bound for the V\'ertesi-Bene-Bell-inequality and the role of POVMs regarding its threshold detection efficiency

Recently, V\'{e}rtesi and Bene [Phys. Rev. A. {\bf 82}, 062115 (2010)] derived a two-qubit Bell inequality, $I_{CH3}$, which they show to be maximally violated only when more general positive operator valued measures (POVMs) are used instead of the usual von Neumann measurements. Here we consider a general parametrization for the three-element-POVM involved in the Bell test and obtain a higher quantum bound for the $I_{CH3}$-inequality. With a higher quantum bound for $I_{CH3}$, we investigate if there is an experimental setup that can be used for observing that POVMs give higher violations in Bell tests based on this inequality. We analyze the maximum errors supported by the inequality to identify a source of entangled photons that can be used for the test. Then, we study if POVMs are also relevant in the more realistic case that partially entangled states are used in the experiment. Finally, we investigate which are the required efficiencies of the $I_{CH3}$-inequality, and the type of measurements involved, for closing the detection loophole. We obtain that POVMs allow for the lowest threshold detection efficiency, and that it is comparable to the minimal (in the case of two-qubits) required detection efficiency of the Clauser-Horne-Bell-inequality.Comment: 11 Pages, 16 Figure

Accelerating Cold Dark Matter Cosmology (ΩΛ≡0\Omega_{\Lambda}\equiv 0)

A new kind of accelerating flat model with no dark energy that is fully dominated by cold dark matter (CDM) is investigated. The number of CDM particles is not conserved and the present accelerating stage is a consequence of the negative pressure describing the irreversible process of gravitational particle creation. A related work involving accelerating CDM cosmology has been discussed before the SNe observations [Lima, Abramo & Germano, Phys. Rev. D53, 4287 (1996)]. However, in order to have a transition from a decelerating to an accelerating regime at low redshifts, the matter creation rate proposed here includes a constant term of the order of the Hubble parameter. In this case, $H_0$ does not need to be small in order to solve the age problem and the transition happens even if the matter creation is negligible during the radiation and part of the matter dominated phase. Therefore, instead of the vacuum dominance at redshifts of the order of a few, the present accelerating stage in this sort of Einstein-de Sitter CDM cosmology is a consequence of the gravitational particle creation process. As an extra bonus, in the present scenario does not exist the coincidence problem that plagues models with dominance of dark energy. The model is able to harmonize a CDM picture with the present age of the universe, the latest measurements of the Hubble parameter and the Supernovae observations.Comment: 9 pages, 6 figures, typos corrected, references added, discussion in Appendix B extende