Emergent universe revisited through the CSL theory

In this work we analyze how the spectrum of primordial scalar perturbations is modified, within the emergent universe scenario, when a particular version of the Continuous Spontaneous Localization (CSL) model is incorporated as the generating mechanism of initial perturbations, providing also an explanation to the quantum-to-classical transition of such perturbations. On the other hand, a phase of super-inflation, prior to slow-roll inflation, is a characteristic feature of the emergent universe hypothesis. In recent works, it was shown that the super-inflation phase could generically induce a suppression of the temperature anisotropies of the CMB at large angular scales. We study here under what conditions the CSL maintains or modifies these characteristics of the emergent universe and their compatibility with the CMB observations.

The Relevance of Thomas Berry for 21st Century Catholicity

The ecological crisis continues to be identified as the most significant social breakdown in the world. One of the important foundational influences on the development of an adequate religious response is the thought of cultural historian Thomas Berry. He affirmed the critical role that the world’s religions have in developing a spirituality that supports the sacrifices, visions, and dreams needed to live in an integral way with the Earth’s community of life. Such a spirituality provides the psychic energies we need to adequately respond to the crisis. The author of this article argues that Berry’s thoughts continue to be relevant, especially in the context of the emergence of a renewed sense of Catholicity. This article presents an overview of the breadth and depth of the study that led to Berry’s articulation of a new human orientation needed to reverse the path of devastation. It offers Berry’s insights into the reasons why it is difficult for Christianity to effectively respond to the present crisis and calls for a new Catholicity that functions out of the comprehensive context of an evolutionary and emergent universe.

Emergent universe in $$D \ge 4$$ dimensions with dynamical wormholes

We present a flat emergent universe (EU) in Einstein gravity with non-linear equation of state (nEoS) in the usual four and in higher dimensions. The EU is assumed to evolve from an initial Einstein’s static universe (ESU) in the infinite past. For a homogeneous Ricci scalar we determine the shape function and obtain a new class of dynamical wormholes that permits EU. The nEoS $$p= A\rho -B \sqrt{\rho _o \rho }$$ p = A ρ - B ρ o ρ is equivalent to three different cosmic fluids which is identified with barotropic fluid for a given A. We obtain EU models in flat, closed and open universes and tested the null energy condition (NEC). At the throat of the wormhole which is recognized as the seed of ESU, we tested the NEC for a given size of the neck. As the EU evolves from an asymptotic past and approaches $$t=0$$ t = 0 , it is found that NEC does not respect. This triggers the onset of interactions at $$t=t_i$$ t = t i , and a realistic flat EU scenario can be obtained in four and in higher dimensions. The origin of the ESU at the throat of the wormhole is also explored via a gravitational instanton mechanism. We compare the relative merits of dynamical wormholes for implementing EU.

Particle creation in the context of the emergent universe

We study the mechanism of particle creation in the context of the emergent universe (EU) scenario which is privileged by certain important characteristics such as the absence of time-like singularity. EU asymptotically coincides with an Einstein static model in the infinite past and it approaches to a de Sitter expansion phase at late times. By introducing the conformal time, we obtain the solution of the Klein-Gordon equation and by applying the "in" and "out" states method, the total number of produced particles and the total energy associated with them are determined.

Emergent universe and Genesis from the DHOST cosmology

In this article, we present an emergent universe scenario that can be derived from DHOST cosmology. The universe starts asymptotically Minkowski in the far past just like the regular Galileon Genesis, but evolves to a radiation dominated period at the late stage, and therefore, the universe has a graceful exit which is absent in the regular Galileon Genesis. We analyze the behavior of cosmological perturbations and show that both the scalar and tensor modes are free from the gradient instability problem. We further analyze the primordial scalar spectrum generated in various situations and discuss whether a scale invariance can be achieved.

Observational constraints of emergent universe in f(R,T) gravity with bulk viscosity

Emergent universe (EU) cosmological models with viscosity in a modified gravity which contains a general function [Formula: see text], where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the energy–momentum tensor, respectively, are studied in a flat Friedmann–Robertson–Walker metric. Cosmological solutions are obtained in [Formula: see text] theory of gravity, which represented as [Formula: see text] with bulk viscosity that described by Eckart theory, truncated Israel Stewart theory and full Israel Stewart Theory. The physical and geometrical features of the EU models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are coupling parameters, with bulk viscosity are studied in details. Constraints of the EU models parameters in [Formula: see text] gravity with bulk viscosity are estimated from observational data set. The stability analysis of the equilibrium points admitting cosmological solutions of the dynamical system associated with the evolution in the modified gravity is studied in Eckart theory, truncated Israel Stewart theory and full Israel Stewart theory.

Cosmological singularities in conformal Weyl gravity

In this work, we study the issue of the past and future cosmological singularities in the context of the fourth-order conformal Weyl gravity. In particular, we investigate the emergent universe scenario proposed by Ellis et al., and find the stability conditions of the corresponding Einstein static state using the fixed point approach. We show that depending on the values of the parameters of the conformal Weyl gravity theory, there are possibilities for having initially stable emergent states for an FRW universe with both the positive and negative spatial curvatures. This represents that the conformal Weyl gravity can be free of the initial singularity problem. Then, following Barrow et al., we address the possible types of the finite-time future cosmological singularities. We discuss how these singularities also can be avoided in the context of this theory.