Testing the equation of state for viscous dark energy

Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on some considerations related to hydrodynamics, two different equations of state for dark energy are assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested with the latest astronomical data from type Ia supernovae (Pantheon sample), measurements of the Hubble parameter HðzÞ, baryon acoustic oscillations and cosmic microwave background radiation. In comparison with the ΛCDM model, some different results are obtained and their viability is discussed. The power-law model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic scenario provide good fits in comparison to the ΛCDM model.Ministerio de Economía, Industria y Competitividad (project FIS2016-76363-P)Agencia de Gestión de Ayudas Universitarias y de Investigación (project 2017 SGR 247)CANTATA COST action (grant CA15117

Is exponential gravity a viable description for the whole cosmological history?

Here we analysed a particular type of $F(R)$ gravity, the so-called exponential gravity which includes an exponential function of the Ricci scalar in the action. Such term represents a correction to the usual Hilbert-Einstein action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic Microwave Background and $H(z)$ data, the free parameters of the model are well constrained. The results show that such corrections to General Relativity become important at cosmological scales and at late-times, providing an alternative to the dark energy problem. In addition, the fits do not determine any significant difference statistically with respect to the $\Lambda$CDM model. Finally, such model is extended to include the inflationary epoch in the same gravitational Lagrangian. As shown in the paper, the additional terms can reproduce the inflationary epoch and satisfy the constraints from Planck data.Comment: 20 pages, 6 figures, analysis extended, version published in EPJ

Early Dark Energy with Power-law F(R) Gravity

We study a power-law $F(R)$ gravity with an early dark energy term, that can describe both the early-time and the late-time acceleration of the Universe. We confront this scenario with recent observational data including the Pantheon Type Ia supernovae, measurements of the Hubble parameter $H(z)$ (Cosmic Chronometers), data from Baryon Acoustic Oscillations and standard rulers data from the Cosmic Microwave Background (CMB) radiation. The model demonstrates some achievements in confronting with these observations and can be compared with the $\Lambda$-Cold-Dark-Matter model. In particular, in both models we obtain very close estimates for the Hubble constant $H_0$, but it is not true for $\Omega_m^0$. The early dark energy term supports viability of the considered $F(R)$ gravity model.Comment: PLB Accepte

Exponential F(R) gravity with axion dark matter

The cosmological evolution within the framework of exponential $F(R)$ gravity is analysed by assuming two forms for dark matter: (a) a standard dust-like fluid and (b) an axion scalar field. As shown in previous literature, an axion-like field oscillates during the cosmological evolution but can play the role of dark matter when approaching the minimum of its potential. Both scenarios are confronted with recent observational data including the Pantheon Type Ia supernovae, Hubble parameter estimations (Cosmic Chronometers), Baryon Acoustic Oscillations and Cosmic Microwave Background distances. The models show great possibilities in describing these observations when compared with the $\Lambda$CDM model, supporting the viability of exponential $F(R)$ gravity. The differences between both descriptions of dark matter is analysed.Comment: 13 pages, 3 figures. To be published in Phys. Dark Univers

Modified Equations of State for Dark Energy and Observational Limitations

Cosmological models with variable and modified equations of state for dark energy are confronted with observational data, including Type Ia supernovae, Hubble parameter data H(z) from different sources, and observational manifestations of cosmic microwave background radiation (CMB). We consider scenarios generalizing the ΛCDM, wCDM, and Chevallier–Polarski–Linder (CPL) models with nonzero curvature and compare their predictions. The most successful model with the dark energy equation of state w=w0+w1(1−a2)/2 was studied in detail. These models are interesting in possibly alleviating the Hubble constant H0 tension, but they achieved a modest success in this direction with the considered observational data

Early dark energy with power-law F(R) gravity

We study a power-law F(R) gravity with an early dark energy term, that can describe both the early-time and the late-time acceleration of the Universe. We confront this scenario with recent observational data including the Pantheon Type Ia supernovae, measurements of the Hubble parameter H(z) (Cosmic Chronometers), data from Baryon Acoustic Oscillations and standard rulers data from the Cosmic Microwave Background (CMB) radiation. The model demonstrates some achievements in confronting with these observations and can be compared with the Λ-Cold-Dark-Matter model. In particular, in both models we obtain very close estimates for the Hubble constant H0, but it is not true for Ωm0. The early dark energy term supports viability of the considered F(R) gravity model

Early dark energy with power-law F(R) gravity

We study a power-law F (R) gravity with an early dark energy term, that can describe both the earlytime and the late-time acceleration of the Universe. We confront this scenario with recent observational data including the Pantheon Type Ia supernovae, measurements of the Hubble parameter H(z) (Cosmic Chronometers), data from Baryon Acoustic Oscillations and standard rulers data from the Cosmic Microwave Background (CMB) radiation. The model demonstrates some achievements in confronting with these observations and can be compared with the -Cold-Dark-Matter model. In particular, in both models we obtain very close estimates for the Hubble constant H0, but it is not true for 0m. The early dark energy term supports viability of the considered F (R) gravity model.This work was partially supported by MICINN (Spain), project PID2019-104397GB-I00 and by the program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M, Spain (SDO).Peer reviewe

Testing viable extensions of Einstein–Gauss–Bonnet gravity

Some models within the framework of Gauss–Bonnet gravities are considered in the presence of a non-minimally coupled scalar field. By imposing a particular constraint on the scalar field coupling, a class of these theories called Einstein–Gauss–Bonnet gravity keeps the correct speed of propagation for gravitational waves. The cosmological evolution for this viable class of models is studied and compared with observational data (BAO, CMB, Sne Ia,.), where we obtain the corresponding bounds for these theories and show that such theories fit well the data and provide a well-behaved cosmological evolution in comparison to the standard model of cosmology. Some statistical parameters show that the goodness of the fits are slightly better than those for ΛCDM model.This work was supported in part by MCIN/AEI/10.13039/501100011033 (Spain), projects PID2019-104397GB-I00 (SDO) and PID2020-117301GA-I00 (DS-CG) and was partially supported by the program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M (SDO). DS-CG is funded by the University of Valladolid (Spain) Ref. POSTDOC UVA20

Exponential F(R) gravity with axion dark matter

The cosmological evolution within the framework of exponential () gravity is analysed by assuming two forms for dark matter: (a) a standard dust-like fluid and (b) an axion scalar field. As shown in previous literature, an axion-like field oscillates during the cosmological evolution but can play the role of dark matter when approaching the minimum of its potential. Both scenarios are confronted with recent observational data including the Pantheon Type Ia supernovae, Hubble parameter estimations (Cosmic Chronometers), Baryon Acoustic Oscillations and Cosmic Microwave Background distances. The models show great possibilities in describing these observations when compared with the CDM model, supporting the viability of exponential () gravity. The differences between both descriptions of dark matter is analysed.This work was partially supported by projects Ref. PID2019-104397GB-I00 (SDO) and Ref. PID2020-117301GA-I00 (DS-CG) funded by MCIN/AEI/10.13039/501100011033 (“ERDF A way of making Europe” and “PGC Generación de Conocimiento”, Spain) and also by the program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M, Spain (SDO).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001058-M).Peer reviewe