Browsing by Author "Hernandez-Almada, A."

Now showing 1 - 7 of 7
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    Barrow Entropy Cosmology: an observational approach with a hint of stability analysis
    (2021) Leon, Genly; Magana, Juan; Hernandez-Almada, A.; Garcia-Aspeitia, Miguel A.; Verdugo, Tomas; Motta, V
    In this work, we use an observational approach and dynamical system analysis to study the cosmological model recently proposed by Saridakis (2020), which is based on the modification of the entropy-area black hole relation proposed by Barrow (2020). The Friedmann equations governing the dynamics of the Universe under this entropy modifica-tion can be calculated through the gravity-thermo dynamics conjecture. We investigate two models, one considering only a matter component and the other including matter and ra-diation, which have new terms compared to the standard model sourcing the late cosmic acceleration. A Bayesian analysis is performed in which using five cosmological observations (observational Hubble data, type Ia supernovae, HII galaxies, strong lensing systems, and baryon acoustic oscillations) to constrain the free parameters of both models. From a joint analysis, we obtain constraints that are consistent with the standard cosmological paradigm within 2a-confidence level. In addition, a complementary dynamical system analysis using local and global variables is developed which allows obtaining a qualitative description of the cosmology. As expected, we found that the dynamical equations have a de Sitter solution at late times.
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    Cosmic acceleration in unimodular gravity
    (2019) Garcia-Aspeitia, Miguel A.; Martinez-Robles, C.; Hernandez-Almada, A.; Magana, Juan; Motta, V
    We study unimodular gravity in the context of cosmology, particularly some interesting consequences that might be able to describe the background cosmology and the late cosmic acceleration. We focus our attention on the hypothesis of nonconservation of the energy momentum tensor. This characteristic has an interesting outcome: we can obtain a modified Friedmann equation along with the acceleration equation and also new fluid equations related to a third order derivative of the scale factor, known in cosmography as the jerk parameter. As a consequence of this theory, it seems that radiation and the cosmological constant are intimately related, in agreement with what some authors have called the third coincidence problem. Their connection is the parameter z(ini), which has a value of 11.29 and coincides with the reionization epoch. As a result, we are able to explain the late acceleration as a natural consequence of the equations, associating the new fluid with radiation and, thus, eliminating the need for another component (i.e., dark energy). Finally, we interpret the results and discuss the pros and cons of using the cosmological constant under the hypothesis of nonconservation of the energy momentum tensor in the unimodular gravity scenario.
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    Generalized emergent dark energy: observational Hubble data constraints and stability analysis
    (2020) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V
    Recently, a phenomenologically emergent dark energy (PEDE) model was presented with a dark energy density evolving as (Omega) over tilde (DE)(z) = Omega(DE,0)[1 - tanh(log(10)(1 + z))], i.e. with no degree of freedom. Later on, a generalized model was proposed by adding one degree of freedom to the PEDE model, encoded in the parameter Delta. Motivated by these proposals, we constrain the parameter space (h, Omega((0))(m)) and (h, Omega((0))(m), Delta) for PEDE and generalized emergent dark energy (GEDE), respectively, by employing the most recent observational (non-)homogeneous and differential age Hubble data. Additionally, we reconstruct the deceleration and jerk parameters and estimate yield values at z = 0 of q(0) = -0.784(-0.027)(+0.028) and j(0) = 1.241(-0.149)(+0.164) for PEDE and q(0) = -0.730(-0.067)(+0.059) and j(0) = 1.293(-0.187)(+0.194) for GEDE using the homogeneous sample. We report values on the deceleration-acceleration transition redshift with those reported in the literature within 2 sigma CL. Furthermore, we perform a stability analysis of the PEDE and GEDE models to study the global evolution of the Universe around their critical points. Although the PEDE and GEDE dynamics are similar to the standard model, our stability analysis indicates that in both models there is an accelerated phase at early epochs of the Universe evolution.
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    Kaniadakis-holographic dark energy: observational constraints and global dynamics
    (2022) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V; Saridakis, Emmanuel N.; Yesmakhanova, Kuralay
    We investigate Kaniadakis-holographic dark energy by confronting it with observations. We perform a Markov Chain Monte Carlo analysis using cosmic chronometers, supernovae type Ia, and Baryon Acoustic Oscillations data. Concerning the Kaniadakis parameter, we find that it is constrained around zero, namely around the value in which Kaniadakis entropy recovers standard Bekenstein-Hawking one. Additionally, for the present matter density parameter Omega((0))(m), we obtain a value slightly smaller compared to Lambda CDM scenario. Furthermore, we reconstruct the evolution of the Hubble, deceleration, and jerk parameters extracting the deceleration-acceleration transition redshift as z(T) = 0.86(-0.14)(+0.21). Finally, performing a detailed local and global dynamical system analysis, we find that the past attractor of the Universe is the matter-dominated solution, while the late-time stable solution is the dark-energy-dominated one.
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    Observational constraints and dynamical analysis of Kaniadakis horizon-entropy cosmology
    (2022) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V; Saridakis, Emmanuel N.; Yesmakhanova, Kuralay; Millano, Alfredo D.
    We study the scenario of Kaniadakis horizon-entropy cosmology, which arises from the application of the gravity-thermodynamics conjecture using the Kaniadakis modified entropy. The resulting modified Friedmann equations contain extra terms that constitute an effective dark energy sector. We use data from cosmic chronometers, Type Ia supernova, H II galaxies, strong lensing systems, and baryon acoustic oscillation observations, and we apply a Bayesian Markov chain Monte Carlo analysis to construct the likelihood contours for the model parameters. We find that the Kaniadakis parameter is constrained around 0, namely around the value where the standard Bekenstein-Hawking is recovered. Concerning the normalized Hubble parameter, we find h = 0.708(-0.011)(+0.012), a result that is independently verified by applying the H0(z) diagnostic and, thus, we conclude that the scenario at hand can alleviate the H-0 tension problem. Regarding the transition redshift, the reconstruction of the cosmographic parameters gives z(T) = 0.715(-0.041)(+0.042). Furthermore, we apply the Akaike, Bayesian, and deviance information criteria, and we find that in most data sets the scenario is statistical equivalent to Lambda cold dark matter one. Moreover, we examine the big bang nucleosynthesis, and we show that the scenario satisfies the corresponding requirements. Additionally, we perform a phase-space analysis, and we show that the Universe past attractor is the matter-dominated epoch, while at late times the Universe results in the dark-energy-dominated solution. Finally, we show that Kaniadakis horizon-entropy cosmology accepts heteroclinic sequences, but it cannot exhibit bounce and turnaround solutions.
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    Stability analysis and constraints on interacting viscous cosmology
    (2020) Hernandez-Almada, A.; Garcia-Aspeitia, Miguel A.; Magana, Juan; Motta, V
    In this work, we study the evolution of a spatially flat Universe by considering a viscous dark matter and perfect fluids for dark energy and radiation, including an interaction term between dark matter and dark energy. In the first part, we analyze the general properties of the Universe by performing a stability analysis, and then we constrain the free parameters of the model using the latest and cosmological-independent measurements of the Hubble parameter. We find consistency between the viscosity coefficient and the condition imposed by the second law of the thermodynamics. The second part is dedicated to constraining the free parameter of the interacting viscous model (IVM) for three particular cases: the viscous model (VM), interacting model (IM), and the perfect fluid case [Lambda-Cold Dark Matter (LCDM)]. We report the deceleration parameters as q(0) = -0.54(-0.05)(+0.06)-0.58(-0.04)(+0.05), -0.58(-0.05)(+0.05), and -0.63(-0.02)(+0.02), together with the jerk parameters as j(0) = 0.87(-0.09)(+0.06), 0.94(-0.06)(+0.04), 0.91(-0.10)(+0.06), and 1.0 for the IVM, VM, IM, and LCDM respectively, where the uncertainties correspond at 68% confidence level. It is worth mentioning that all the particular cases are in good agreement with LCDM, in some cases producing even better fits, with the advantage of eliminating some problems that afflict the standard cosmological model.
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    The Universe acceleration from the Unimodular gravity view point: Background and linear perturbations
    (2021) Garcia-Aspeitia, Miguel A.; Hernandez-Almada, A.; Magana, Juan; Motta, V
    With the goal of studying the cosmological constant (CC) problem, we present an exhaustive analysis of unimodular gravity as a possible candidate to resolve the CC origin and with this, the current Universe acceleration. In this theory, a correction constant (CC-like) in the field equations sources the late cosmic acceleration. This constant is related to a new parameter, z(ini), which is interpreted as the redshift of CC-like emergence. By comparing with the CC value obtained from Planck and Supernovaes measurements, it is possible to estimate z(ini) = 11.15(-0.02)(+0.01) and z(ini) = 11.43(-0.06)(+0.03) respectively, which is close to the reionization epoch. Moreover, we use the observational Hubble data (OHD), Type Ia Supernovae (SnIa), Baryon Acoustic Oscillations (BAO) and the Cosmic Microwave Background Radiation (CMB) distance data to constrain the UG cosmological parameters. A Joint analysis (OHD+SnIa+BAO+CMB), results in z(ini) = 11.47(-0.073)(+0.074) within 1 sigma confidence level consistent with our estimation from Planck and Supernovae measurements. We also include linear perturbations, starting with scalar and tensor perturbations and complementing with the perturbed Boltzmann equation for photons. We show that the 00 term in the UG field equations and the Boltzmann equation for photons contains corrections, meanwhile the other equations are similar as those obtained in standard cosmology. (C) 2021 Elsevier B.V. All rights reserved.