Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.

Cosmological Polytopes and the Wavefuncton of the Universe for Light States

Abstract: We extend the investigation of the structure of the late-time wavefunction of the universe to a class of toy models of scalars with time-dependent masses and polynomial couplings, which contains general massive scalars in FRW cosmologies. We associate a universal integrand to each Feynman diagram contributing to the wavefunction of the universe. For certain (light) masses, such an integrand satisfies recursion relations involving differential operators, connecting states with different masses and having, as a seed, the massless scalar (which describes a conformally coupled scalar as a special case). We show that it is a degenerate limit of the canonical form of a generalisation of the cosmological polytopes describing the wavefunction for massless scalars. Intriguingly, the flat-space scattering amplitude appears as a higher codimension face: it is encoding the leading term in the Laurent expansion as the total energy is taken to zero, with the codimension of the face providing the order of the total energy pole. The same connection between the other faces and the Laurent expansion coefficients holds for the other singularities of the wavefunction of the universe, all of them connectable to flat-space processes. As the degenerate limit is taken, some of the singularities of the canonical form of the polytope collapse onto each other generating higher order poles. Finally, we consider the mass as a perturbative coupling, showing that the contribution to the wavefunction coming from graphs with mass two-point couplings can be identified with a degenerate limit of the canonical form of the cosmological polytope, if the perturbative expansion is done around the conformally coupled state; or as double degenerate limit of the canonical form of the extension of the cosmological polytopes introduced in the present paper, if the perturbative expansion is done around minimally coupled states.

The Rise of Cosmological Complexity: Saturation of Growth and Chaos

Abstract: We compute the circuit complexity of scalar curvature perturbations on FLRW cosmological backgrounds with fixed equation of state $w$ using the language of squeezed vacuum states. Backgrounds that are accelerating and expanding, or decelerating and contracting, exhibit features consistent with chaotic behavior, including linearly growing complexity. Remarkably, we uncover a bound on the growth of complexity for both expanding and contracting backgrounds $\lambda \leq \sqrt{2} \ |H|$, similar to other bounds proposed independently in the literature. The bound is saturated for expanding backgrounds with an equation of state more negative than $w = -5/3$, and for contracting backgrounds with an equation of state larger than $w = 1$. For expanding backgrounds that preserve the null energy condition, de Sitter space has the largest rate of growth of complexity (identified as the Lyapunov exponent), and we find a scrambling time that is similar to other estimates up to order one factors.

On the Degree of Generality of Inflation in Friedmann Cosmological Models with a Massive Scalar Field

Abstract: Friedmann cosmological models with a massive minimally coupled scalar field are investigated by numerical methods. It is indicated that the majority of the solutions undergo the inflationary stage in flat and open models. In a closed model the ratio of the number of solutions without adequate inflation to the number of the total solutions are obtained numerically. I ) One oL the questions concerning this model is a generality of the inflationary solutions. We investigate this problem studying classical solutions of a homogeneous model with a massive scalar field. Among all solutions in this model some are inflationary and the others are not. If it is found that a fraction of the inflationary solutions (the ratio of the number of the inflationary solutions to the total number of solutions in some measure) is large enough, it becomes very reasonable to take such solutions for the model of our universe. For the flat Friedmann-Robertson-Walker (FRW) models, this problem was treated in the paper by Belinsky, Grishchuk, Zel'dovich and Khalatnikov. 2 ) Analyz­ ing the behavior of trajectories in the phase space of this dynamical system, they have shown that a fraction of the non-inflationary solution is the order of m/mp, mp and m being the Planck mass and a mass of the scalar field respectively. In fact, in order for the density fluctuation generated during the inflation to be small, the ratio m/mp is restricted to be smalI"such as m/mp~ 1O-5~ 10- 6 • 4 ) Therefore, at least for the flat FRW model, the overwhelming majority of the solutions are found to be inflationary. N ow, as for the open and closed FRW models, the problem was treated by the analytic method in the paper by Belinsky and Khalatnikov. 5 ) For the open model, the result is not so different from the flat model. However, for the closed model, the result is quite different: Due to the curvature effect, the expansion tends to turn into collapse. In the previous work, it was shown that the fra<;:tion of the non-inflationary solution is about 1/4 in some measure. In this paper, we investigate the evolution of the universe.modelsby an.explicit numerical computation of the phase space trajectories and have confirmed the.results of the previous work. The phase space for open and closed models is three dimen­ sional and the trajectories start from the two dimensional surface called "Quantum

Cosmological consequences in the framework of generalized Rastall theory of gravity

Abstract: The paper deals with generalized Rastall theory of gravity and its cosmological consequences in the background of homogeneous and isotropic flat FLRW model with perfect fluid as the matter context. The model shows a non singular era (emergent scenario) at the early phase of expansion for a particular choice of the Rastall parameter. Also the model finds to be equivalent to the particle creation mechanism in Einstein gravity in the framework of non-equilibrium thermodynamics. Universal thermodynamics is briefly presented and it is found that the entropy function in Rastall theory is the usual Bekenstein entropy and there is no correction to it. Finally, a complete cosmic history starting from inflation to late time acceleration is presented for suitable choices of the Rastall parameter.