Dark energy, matter creation and curvature

Cárdenas, Víctor H.

doi:10.1140/epjc/s10052-012-2149-0

Cited by 50 publications

(15 citation statements)

References 36 publications

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“…Therefore, the mechanism is capable to accelerate the Universe, without the need of an additional dark energy component. An alternative cosmological model, which assumes the existence of gravitational particle creation was studied in [27]. The model fits well the supernova observations.…”

Section: +007mentioning

confidence: 72%

Thermodynamic interpretation of the generalized gravity models with geometry-matter coupling

2014

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Modified gravity theories with geometry -matter coupling, in which the action is an arbitrary function of the Ricci scalar and the matter Lagrangian (f (R, Lm) gravity), and of the Ricci scalar and of the trace of the matter energy-momentum tensor (f (R, T ) gravity), respectively, have the intriguing property that the divergence of the matter energy -momentum tensor is nonzero. In the present paper, by using the formalism of open thermodynamic systems, we interpret the generalized conservation equations in these gravitational theories from a thermodynamic point of view as describing irreversible matter creation processes, which could be validated by fundamental particle physics. Thus particle creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents, with the second law of thermodynamics requiring that space-time transforms into matter. The equivalent particle number creation rates, the creation pressure and the entropy production rates are obtained for both f (R, Lm) and f (R, T ) gravity theories. The temperature evolution laws of the newly created particles are also obtained. In the case of the f (R, T ) gravity theory the open irreversible thermodynamic interpretation of a simple cosmological model is presented in detail. It is also shown that due to the geometry-matter coupling, during the cosmological evolution a large amount of comoving entropy could be produced.

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Section: +007mentioning

confidence: 72%

Thermodynamic interpretation of the generalized gravity models with geometry-matter coupling

2014

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“…Particle creation models [9,10,[12][13][14][15][16][17][18], as the one treated in this work, should also not be confused with other cosmological scenarios where particle production is present, like, e.g., in warm inflation [19]. In warm inflation models the inflationary evolution can be strongly influenced by relativistic (radiation) particle production.…”

Section: Introductionmentioning

confidence: 99%

Matter creation and cosmic acceleration

2014

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We investigate the creation of cold dark matter (CCDM) cosmology as an alternative to explain the cosmic acceleration. Particular attention is given to the evolution of density perturbations and constraints coming from recent observations. By assuming negligible effective sound speed we compare CCDM predictions with redshift-space-distortion based f(z) sigma_8(z) measurements. We identify a subtle issue associated with which contribution in the density contrast should be used in this test and then show that the CCDM results are the same as those obtained with LambdaCDM. These results are then contrasted with the ones obtained at the background level. For the background tests we have used type Ia supernovae data (Union 2.1 compilation) in combination with baryonic acoustic oscillations and cosmic microwave background observations and also measurements of the Hubble parameter at different redshifts. As a consequence of the studies we have performed at both the background and perturbation levels, we explicitly show that CCDM is observationally degenerate with respect to LambdaCDM (dark degeneracy). The need to overcome the lack of a fundamental microscopic basis for the CCDM is the major challenge for this kind of model.Comment: 12 pages, 5 png figure

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“…This section is based on case studies on Colombian agricultural cooperatives, specifically Dávila (1996Dávila ( , 2002Dávila ( , 2004, Coque et al (2000), Ariza and Lobo (2002), Bucheli (2002) and Medina (2002). Furthermore, it analyses recent literature (FAO and CAF 2007;Kalmanovitz and López, 2006), empirical studies (Cárdenas, 2009;Orozco et al, 2013), reports (Confecoop, 2006(Confecoop, , 2007(Confecoop, , 2008(Confecoop, , 2008a(Confecoop, , 2010(Confecoop, , 2011(Confecoop, , 2013DANE, 2009;Econometría, 2011;PNUD, 2011PNUD, , 2012 and public data (MADR, 2010; Supersolidaria, 2011) on rural cooperatives and smallholder farming in Colombia.…”

Section: Introductionmentioning

confidence: 99%

Smallholders’ Agricultural Cooperatives in Colombia: ¿Vehicles for Rural Development?

Rodríguez¹

2014

DyS

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This article focuses on assessing whether the main conditions required for smallholders' agricultural cooperatives to successfully develop are currently met in Colombia. The main objective is to formulate policy implications on how the State may contribute to facilitate that these organizations constitute vehicles for rural development. The article argues that the conditions that facilitate the development of agricultural cooperatives are not adequately achieved in Colombia. Furthermore, it suggests that the State and other external agents may have an important role to play in advancing these conditions. In short, it proposes the formulation of policies that allow the State to exert a facilitating role that aims to "midwife" the formation and development of self-reliant grassroots organizations. This "facilitatory" role would represent a third-way between two previous approaches that have failed in Colombia in the past: the "top-down" interventions on farmer enterprises devised by the State in the 1 Is a Lawyer from Javeriana University. He holds a Master in Law and Economics from

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Dark energy, matter creation and curvature

Cited by 50 publications

References 36 publications

Thermodynamic interpretation of the generalized gravity models with geometry-matter coupling

Thermodynamic interpretation of the generalized gravity models with geometry-matter coupling

Matter creation and cosmic acceleration

Smallholders’ Agricultural Cooperatives in Colombia: ¿Vehicles for Rural Development?

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