Anisotropic Bianchi Type-VI Cosmological Models with Cosmic Strings and Domain Walls in f(R,T) Gravity

Abstract

In this work, we investigate anisotropic cosmological models of Bianchi type-VI in the framework of modified gravity described by the function F(R,T), where R is the Ricci scalar and T is the trace of the energy–momentum tensor. The cosmic matter content is modelled in two physically motivated forms, namely a cloud of cosmic strings with attached particles and thick domain walls. To obtain exact and tractable solutions of the field equations, we assume that the scalar expansion is proportional to the shear scalar and adopt Berman’s law for the variation of the Hubble parameter, which leads to a constant deceleration parameter.
Explicit solutions for the metric functions are derived, and the dynamical behavior of key physical quantities such as the expansion scalar, shear scalar, anisotropy parameter, energy density, string tension density, and pressure are examined. The resulting models exhibit accelerated expansion at late times and are free from initial singularities. It is also found that the universe remains anisotropic throughout its evolution due to the non-vanishing anisotropy parameter. Furthermore, both the energy density and the string tension (or domain wall pressure) decrease with cosmic time and tend toward negligible values in the far future.
These results indicate that Bianchi type-VI cosmological models with cosmic strings and domain walls in F(R,T) gravity provide a consistent theoretical framework for describing an anisotropic, accelerating universe and offer useful insights into the possible role of topological defects in cosmic evolution.