Bianchi type-I cosmology in f(R,T) gravity

We investigate the exact solutions of a Bianchi type-I space-time in the context of f(R, T) gravity [1], where f(R, T) is an arbitrary function of the Ricci scalar R and the trace of the energy-momentum tensor T. For this purpose, we find two exact solutions using the assumption of a constant deceleration parameter and the variation law of the Hubble parameter. The obtained solutions correspond to two different models of the Universe. The physical behavior of these models is also discussed.     

Commentary on "Mechanical properties of monodomain side-chain nematic elastomers" by P. Martinoty, P. Stein, H. Finkelmann, H. Pleiner and H.R. Brand

We discuss the background to static and dynamic soft elasticity. The evidence in the static case and the symmetry basis for soft and semi-soft elasticity is well understood. By contrast the dynamic analogy is less clear. Lack of clean time scale separation clouds the interpretation of director relaxation keeping up, or not, with imposed strains. However, the reduction in modulus between geometries obtaining at low frequencies and being lost at high frequencies confirms that director reaction indeed determines dynamical semi-softness.     

$${f(\mathcal R)}$$ quantum cosmology

We have quantized a flat cosmological model in the context of the metric models, using the causal Bohmian quantum theory. The equations are solved and then we have obtained how the quantum corrections influence the classical equations.     

Relativistic kinetics and cosmology. I

A study is made of the problem of describing the cosmological expansion of a plasma in the framework of Chernikov's relativistic kinetic theory. It is shown that from the point of view of relativistic kinetics there are two stages in the evolution of the Universe in which thermodynamic equilibrium of the plasma is attained asymptotically: 1) the earliest ultrarelativistic stage, and 2) the nonrelativistic stage of the expansion, when the radiation is decoupled from the matter. It is shown that the relativistic kinetics of the plasma expansion at the time of decoupling of the radiation from the matter leads to transfer of energy from the photon component of the plasma to the electron component.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 42–47, August, 1980.     

Space, time, and velocity in cosmology

In the limit of negligible gravity, a transformation that relates physical quantities at different cosmic times, similar to the Lorentz transformation which relates measurments at different velocities, is derived.     

Bouncing cosmology inspired by regular black holes

In this article, we present a bouncing cosmology inspired by a family of regular black holes. This scale-dependent cosmology deviates from the cosmological principle by means of a scale factor which depends on the time and the radial coordinate as well. The model is isotropic but not perfectly homogeneous. That is, this cosmology describes a universe almost homogeneous only for large scales, such as our observable universe.