INVESTIGATING THE HYPERBOLIC AND HYBRID SCALAR FIELD COSMOLOGIES WITH VARYING COSMOLOGICAL CONSTANT IN F(R, T ) GRAVITY

This paper investigated two scalar field cosmological models in f (R, T) gravity with cosmic transit and varying cosmological constant Lambda(t). The cosmological constant tends to have a tiny positive value at the current epoch. The scalar field pressure p phi shows a sign flipping for normal scalar field. For the phantom field, the scalar potential V (phi) is negative and the energy density rho phi = Ek +V takes negative values when the equation of state parameter omega phi is less than 1. The WEC, rho = Sigma i rho i >= 0 and pi + rho i >= 0, is not violated but with an instability for the second model at late times. For a scalar field phi, the condition rho phi + p phi = rho phi(1 + omega phi) = 2Ek >= 0 allows both models. The cosmology in both models was studied using a given function a(t) derived from the desired cosmic behavior, which is the opposite of the traditional view.