Cosmological test on viscous bulk models using Hubble parameter measurements and type Ia supernovae data

Abstract

From a phenomenological point of view, we analyze the dynamics of the Universe at late times by introducing a polynomial and hyperbolic bulk viscosity into the Einstein field equations respectively. We constrain their free parameters using the observational Hubble parameter data and the Type Ia Supernovae dataset to reconstruct the deceleration q and the jerk j parameters within the redshift region 0 < z < 2.5. At current epochs, we obtain q 0 = −0.680 +0.085 −0.102 and j 0 = 2.782 +1.198 −0.741 for the polynomial model and q 0 = −0.539 +0.040 −0.038 (−0.594 +0.056 −0.056 ) and j 0 = 0.297 +0.051 −0.050 (1.124 +0.196 −0.178 ) for the tanh (cosh) model. Furthermore, we explore the statefinder diagnostic that gives us evident differences with respect to the concordance model (LCDM). According to our results this kind of models is not supported by the data over LCDM.

Stability analysis and constraints on interacting viscous cosmology

“…4. We estimate the current values of the cosmographic parameters as q 0 = −0.55 +0.06 −0.05 , −0.58 +0.05 −0.04 , −0.58 +0.05 −0.05 , −0.63 +0.02 −0.02 and j 0 = 0.87 +0.06 −0.09 , 0.94 +0.04 −0.06 , 0.91 +0.06 −0.10 , 1.0, for the IVM, VM, IM, and LCDM respectively, which are in agreement with those reported in the literature considering other models [12,48]. Finally, although our results on BIC suggest the models used are unfavourable over LCDM standard paradigm, they give an alternative to alleviate the CC problems by adding some degree of freedom to LCDM.…”

“…Regarding the cosmographic parameters, we obtain the deceleration one at z = 0 to be q 0 = −0.55 +0.06 −0.05 , −0.58 +0.05 −0.04 , −0.58 +0.05 −0.05 , and −0.63 +0.02 −0.02 for the IVM, VM, IM, and LCDM respectively. When we compare these results with the one obtained by [12] for the LCDM model, values with those obtained by [48] considering viscous models, we find a deviation of about 1.3σ. Additionally, we find a deviation on q 0 within 1.2σ for IVM, IV, and VM to the one value obtained in [76].…”

“…In contrast, the Eckart's scenario was the first proposal to study the relativistic dissipative processes as a first order deviations around the equilibrium and, despite the causality problem, it is widely used due to its simplicity. For instance, some works related to the Eckart's theory, have been investigated the dynamics of the Universe at late times by considering a bulk viscous coefficient with a constant [42][43][44][45], polynomial [46][47][48], and hyperbolic [48,49] forms as functions of the redshift or in terms of the energy density. Additionally, authors in [45,50] have been studied the Universe with several fluids, being a more realistic description of the Universe.…”

Constraints and cosmography of $$\Lambda $$CDM in presence of viscosity

“…where we have used E(0) = Ω(0) = 1, Ω(z) = Ω m0 (1 + z) 3 + Ω de0 , and 2 F 1 is the hypergeometric function. In this work, based on the results obtained on [48] we will set n = −2. For λ 1 = 0, we have the case when the bulk viscosity coefficient is constant; in this case, we obtain…”

“…Although, in the Eckart approach the propagation of the perturbations on the non perfect fluid occurs at infinite speed, it is a simpler theory than the IS formalism, allowing to study more complex forms of the viscosity. For instance, bulk viscosity coefficient has been modelled as a constant [30][31][32][33], polynomials [34][35][36], and hyperbolic [36,37] functions. Moreover, it allows easily to explore the presence of interacting terms in the viscous fluid [38].…”