Anisotropic bulk viscous string cosmological models of the Universe under a time-dependent deceleration parameter

Abstract

We investigate a new class of LRS Bianchi type-II cosmological models by revisiting in the paper of Mishra et al (2013) by considering a new deceleration parameter (DP) depending on the time in string cosmology for the modified gravity theory suggested by Sáez & Ballester (1986). We have considered the energy-momentum tensor proposed by Leteliar (1983) for bulk viscous and perfect fluid under some assumptions. To make our models consistent with recent astronomical observations, we have used scale factor (Sharma et al 2018; Garg et al 2019) a(t) = exp [ 1 β √ 2βt + k], where β and k are positive constants and it provides a time-varying DP. By using the recent constraints (H 0 = 73.8, and q 0 = −0.54) from SN Ia data in combination with BAO and CMB observations (Giostri et al, arXiv:1203.3213v2[astro-ph.CO]), we affirm β = 0.0062 and k = 0.000016. For these constraints, we have substantiated a new class of cosmological transit models for which the expansion takes place from early decelerated phase to the current accelerated phase. Also, we have studied some physical, kinematic and geometric behavior of the models, and have found them consistent with observations and well established theoretical results . We have also compared our present results with those of Mishra et al (2013) and observed that the results in this paper are much better, stable under perturbation and in good agreement with cosmological reflections.

An FLRW interacting dark energy model of the Universe

“…From these discussions, q may not be taken as a constant, but it should be time-dependent. Recently, many researchers [35]− [39] & [60]− [63] have used the time-dependent DP for solving various cosmological problems. So we consider q as a linear function of the Hubble function parameter which was earlier used by [64]− [66] in different context of cosmological models.…”

An Investigation into LRS Bianchi I Universe in Brans-Dicke Theory

“…Moreover, the bulk viscous coefficient has been represented as η. Besides, u i defines 4-velocity of the particle and x i is named unit space-like vector determined the string direction [21,30]. Further, the LRS Bianchi type-I space-time line element can be written as…”

String Viscous Fluid Cosmological Model in the Framework of Sen-Dunn Theory of Gravitation

“…Several researchers have investigated cosmological models that incorporate cosmic strings within the viscous fluid. Hatkar et al (11) , Mishra and Dua (12) , Santhi et al (13) , Bhoyar et al (14) , Hegazy (15) , Trivedi and Bhabor (16) , Dixit et al (17) and Mete and Deshmukh (18) . The behaviour of viscous fluid in the string cosmological model in the Lyra manifold, which takes into account the constant coefficient of bulk viscosity, has recently been explored by Mollah and Singh (19) .…”