Cosmological Bounce Research Articles

Entanglement production through a cosmological bounce

In quantum cosmology, it is expected that the Big Bang singularity is resolved and the universe undergoes a bounce. We find that for Gaussian initial states, matter-gravity entanglement entropy rises rapidly during the bounce, declines, and then approaches a steady-state value following the bounce. These observations suggest that matter-gravity entanglement is a feature of the macroscopic universe and that there is no Second Law of entanglement entropy.

Primordial gravitational waves of big bounce cosmology in light of stochastic gravitational wave background

Primordial gravitational waves of big bounce cosmology in light of stochastic gravitational wave background

Matter bounce cosmology within Finsler-Randers geometry: A comprehensive study of anisotropic influences

In this study, we explore the dynamics of matter bounce cosmology within the framework of Finsler-Randers geometry, focusing on the role of the Finslerian correction term η(t). By integrating Finsler geometry into cosmological models, we introduce anisotropic effects that significantly impact the evolution of the universe, particularly during the bounce phase. The research examines various cosmological parameters, including the deceleration (qη(t)), jerk (jη(t)), and snap (sη(t)) parameters, highlighting the influence of the Finsler correction on these key indicators. Our results demonstrate that the Finslerian framework leads to more complex and abrupt transitions in the universe's expansion dynamics compared to traditional Riemannian models. The study also reveals that the Finslerian correction intensifies the violations of energy conditions, such as the null energy condition (NEC), which are crucial for the occurrence of a successful bounce. Furthermore, the analysis of the squared sound speed vs2 indicates that the model's stability is highly sensitive to the choice of the Finslerian parameters, with certain configurations leading to instability during the bounce. Our findings underscore the unique contributions of Finsler geometry to cosmological models, offering deeper insights into the behavior of the universe under anisotropic influences and providing a potential avenue for addressing longstanding challenges in cosmology.

Cosmological bouncing solutions in f(𝒬,𝒯) theory

This paper examines the behavior of the universe around the bouncing point in the background of [Formula: see text] theory, where [Formula: see text] is the non-metricity and [Formula: see text] is the trace of the energy–momentum tensor. We derive the field equations that describe gravitational phenomena in the existence of non-metricity and matter source terms. By applying the reconstruction method for the Hubble parameter, a phenomenon of the bouncing universe for homogeneous spacetime filled with perfect fluid is studied. We consider specific models of this modified theory to evaluate the behavior of various cosmic parameters such as the Hubble, deceleration, equation of state and fluid parameters. When the null energy condition is violated, it follows a bouncing behavior. It is found that spacetime is composed of isotropic fluid, where a big bounce can occur and the universe turns into extremely unstable. We conclude that [Formula: see text] gravity successfully explains the early and late time cosmic expansion and evolution.

Dual inflation and bounce cosmologies interpretation of pulsar timing array data

We explore a dual scenario of generalized inflation and bounce cosmologies, producing a scale-invariant curvature perturbation spectrum. Bayesian analysis with pulsar timing array data identifies, for the first time, viable regions from inflation and bounce that simultaneously explain stochastic gravitational wave background (SGWB) signals and CMB anisotropies. Bayes factor calculations strongly favor this dual scenario over conventional sources and provide initial evidence of a duality between inflation and bounce regarding SGWB, offering new insights for early universe model-building and future observations.

Viability of reconstructed bouncing cosmologies in f(T,𝒯 ) gravity

Cosmological reconstruction is a powerful technique in modified gravity invented to find the analogy of different cosmological epochs in modified gravity. In this paper, I present the modified holographic reconstruction scheme for [Formula: see text] theory of gravity where [Formula: see text] and [Formula: see text] are the torsion scalar and trace of energy–momentum tensor in the context of flat FRW universe. For this reconstruction, I consider Hubble horizon as an infrared cutoff and focus on a particular model [Formula: see text] (a correction to the teleparallel action depending on the matter content). Within this framework, I consider both the power law scale factor as well as the well-established cosmological bouncing scenario. Further, I explore various gravitational Lagrangians that can be reconstructed to yield analytical solution for symmetric, superbounce, oscillatory, singular bounce and matter bounce settings. The viability of these reconstructed models is then assessed through the EoS parameter [Formula: see text] and the [Formula: see text] plane [Formula: see text]. Notably, all the results align well with recent observational data.

Towards testing the general bounce cosmology with the CMB B-mode auto-bispectrum

It has been shown that a three-point correlation function of tensor perturbations from a bounce model in general relativity with a minimally-coupled scalar field is highly suppressed, and the resultant three-point function of cosmic microwave background (CMB) B-mode polarizations is too small to be detected by CMB experiments. On the other hand, bounce models in a more general class with a non-minimal derivative coupling between a scalar field and gravity can predict the three-point correlation function of the tensor perturbations without any suppression, the amplitude of which is allowed to be much larger than that in general relativity. In this paper, we evaluate the three-point function of the B-mode polarizations from the general bounce cosmology with the non-minimal coupling and show that a signal-to-noise ratio of the B-mode auto-bispectrum in the general class can reach unity for ℓ max=100 in the full-sky case, with and without the lensing B-mode added to cosmic variance. Considering additionally the LiteBIRD experimental noise, we obtain a SNR smaller than unity.

Cosmological bounce scenario with a novel parametrization of bulk viscosity

Cosmological bounce scenario with a novel parametrization of bulk viscosity

An investigation of inflationary and bounce cosmology within the context of f(Q) gravity

In this work, we have examined the metric affine-based geometric model [Formula: see text] to investigate inflationary cosmology and bouncing cosmology. The four bouncing models we have examined are the exponential, matter, symmetric and super-bounce models. Furthermore, in the inflationary situation, we have employed a scalar field to test whether or not kinetic energy is dominated and whether or not all of the bouncing models are consistent with inflationary conditions. We have investigated various energy conditions for various scale factors and verified whether or not these scale factors are consistent with inflationary scenarios within the framework of inflationary cosmology under [Formula: see text]. In the end, we have shown that the bouncing scale factor under the polynomial model ([Formula: see text]) of [Formula: see text] gravity in a single scalar field is compatible with the inflationary scenario.

Comprehensive study of bouncing cosmological models in f(Q, T) theory

The main objective of this article is to investigate the viability of bouncing cosmological scenarios using different forms of scale factors with perfect matter configuration in the framework of extended symmetric teleparallel theory. This modified proposal is defined by the function f(Q, T), where Q characterizes non-metricity and T denotes the trace of energy-momentum tensor. We investigate the modified field equations of this theory using different parametric values of the Hubble parameter and non-metricity to derive viable solutions. These solutions are relevant in various cosmological bounce models such as symmetric-bounce, super-bounce, oscillatory-bounce, matter-bounce and exponential-bounce models. Furthermore, we examine the behavior of energy density and pressure to analyze the characteristics of dark energy. A comprehensive analysis is also conducted to explore the behavior of the equation of state parameter and deceleration parameter to examine the evolutionary eras of the cosmos. Our findings show that the f(Q, T) gravity describes the cosmic expansion in the vicinity of the bouncing point during the early and late times of cosmic evolution.

Unruh-DeWitt particle detectors in bouncing cosmologies

We study semi-classical particle production in non-singular bouncing cosmologies by employing the Unruh-DeWitt model of a particle detector propagating in this class of spacetimes. The scale factor for the bouncing cosmology is derived analytically and is inspired by the modified Friedmann equation employed in the loop quantum cosmology literature. We examine how the detector response varies with the free parameters in this model such as the equation of state during the contraction phase and the critical energy density during the bounce phase. We also investigate whether such a signature in the particle detector survives at late times.

Reconstruction of the singularity-free f(R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f({\\mathcal {R}})$$\\end{document} gravity via Raychaudhuri equations

We study the bounce cosmology to construct a singularity-free f(R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f({\\mathcal {R}})$$\\end{document} model using the reconstruction technique. The formulation of the f(R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f({\\mathcal {R}})$$\\end{document} model is based on the Raychaudhari equation, a key element employed in reconstructed models to eliminate singularities. We explore the feasibility of obtaining stable gravitational Lagrangians, adhering to the conditions fR>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_{{\\mathcal {R}}}>0$$\\end{document} and fRR>0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$f_{{\\mathcal {R}}{\\mathcal {R}}}>0$$\\end{document}. Consequently, both models demonstrate stability, effectively avoiding the Dolgov–Kawasaki instability. Our assessment extends to testing the reconstructed model using energy conditions and the effective equation-of-state (EoS). Our findings indicate that the reconstructed super-bounce model facilitates the examination of a singularity-free accelerating universe for both phantom and non-phantom phases. However, in the case of the reconstructed oscillatory bounce model, two scenarios are considered with ω=-1/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega =-\\,1/3$$\\end{document} and ω=-2/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega =-\\,2/3$$\\end{document}. While the model proves suitable for studying a singular-free accelerating universe in the ω=-1/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega =-\\,1/3$$\\end{document} case, it fails to demonstrate such behavior under energy conditions for the ω=-2/3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega =-\\,2/3$$\\end{document} scenario. The reconstructed models accommodate early-time bouncing behavior and late-time cosmic acceleration within a unified framework.

Modified Friedmann equations from Maxwell-Weyl gauge theory

This study investigates the possibility of a homogeneous and isotropic cosmological solution within the context of the Maxwell-Weyl gauge theory of gravity. To achieve this, we utilize the Einstein-Yang-Mills theory as an analogy and represent the Maxwell gauge field in terms of two time-dependent scalar fields. We derive the modified Friedmann equations, integrating the contributions from the Maxwell gauge fields and an effective cosmological constant that depends on the Dirac scalar field. Our analysis reveals how these modifications influence various cosmological scenarios, including power-law evolution, de Sitter-like expansion, inflationary phases, non-singular bounce cosmologies, and cyclic cosmologies.

Parity violation in primordial tensor non-Gaussianities from matter bounce cosmology

It has been shown that primordial tensor non-Gaussianities from a cubic Weyl action with anon-dynamical coupling are suppressed by the so-called slow-roll parameter in a conventional framework of slow-roll inflation. In this paper, we consider matter bounce cosmology in which the background spacetime is no longer quasi-de Sitter, and hence one might expect that the matter bounce models could predict non-suppressed non-Gaussianities. Nevertheless, we first show that the corresponding non-Gaussian amplitudes from the cubic Weyl term with a non-dynamical coupling are much smaller than those from the conventional slow-roll inflation, in spite of the fact that there is no slow-roll suppression. We then introduce a dynamical coupling that can boost the magnitude of graviton cubic interactions and clarify that there is a parameter region where the tensor non-Gaussianities can be enhanced and can potentially be tested by cosmic microwave background experiments.

On the evolution of the volume in Loop Quantum Cosmology

The dynamics of the expectation value of the volume is one of the key ingredients behind the replacement of the Big Bang singularity by a bounce in Loop Quantum Cosmology. As such, it is of great importance that this quantity is mathematically well-defined in the space of physical states of the theory. A number of caveats have been raised about such a definition entering in conflict with the quantum evolution of states, motivated by the situation found in quantum geometrodynamics. We show that there are ways around these caveats, all of which are related to the existence of quantization prescriptions leading to a nondegenerate curvature operator in Loop Quantum Cosmology. Interestingly, the properties of the curvature operator that may allow for a good behavior of the volume are only possible thanks to the discreteness of the geometry characteristic of the loop quantization procedure.

Implementation of cosmological bounce inflation with Nojiri–Odintsov generalized holographic dark fluid

This work reports a study on bounce cosmology with a highly generalized holographic dark fluid inspired by Nojiri and Odintsov [Eur. Phys. J. C 77 (2017) 1–8]. The holographic dark fluid that is mostly used for late-time acceleration has been implemented to reconstruct toward realization of cosmological bounce. We first used the most generalized Nojiri–Odintsov (NO) cutoff to implement the holographic dark fluid. Accordingly, we have reconstructed this dark fluid via some solutions of scale factors. With those solutions, we have explored the evolution of different cosmological parameters. We have examined the effects of each reconstructed parameter in the context of the realization of the cosmic bounce. Next, we use the analytical inferences of the scalar spectral index, tensor-to-scalar ratio, and slow-roll characteristics of the model to study a bounce inflationary scenario. Since inflation is usually associated with the existence of scalar fields, we looked at a possible relationship between NO generalized holographic dark energy and scalar field models. Plotting the evolution of the potential results from the scalar fields against time. Finally, we investigated the GSL of thermodynamics in the pre- and post-bounce scenarios.

The dynamics of matter bounce cosmology in Weyl-type [formula omitted] gravity

In this work, we investigate the dynamics of bouncing cosmologies within the framework of Weyl-type f(Q,T) gravity. Here, Q represents the non-metricity of the space–time, is determined by the vector field wμ, while T represents the trace of the matter energy–momentum tensor. Our objective is to explore the feasibility of avoiding the Big Bang singularity by implementing a matter-bounce cosmology. To achieve this, we consider a specific model with the functional form f(Q,T)=αQ+β6κ2T, where α and β are model parameters. We analyze the dynamical parameters associated with this model and examine the influence of the Weyl-type f(Q,T) theory on these parameters. Moreover, we assess the stability of the proposed model to ensure its viability as a cosmological scenario. Through our analysis, we aim to gain insights into the potential implications and consequences of Weyl-type f(Q,T) gravity for bouncing scenarios, contributing to our understanding of alternative gravitational theories in the context of cosmology.

Dark torsion oscillations and bounces induced by Barbero-Immirzi and quantum correction on Einstein-Cartan gravity with very light inflatons

In this paper we present several examples of how to constrain loop quantum gravity Barbero-Immirzi (BI) parameter, either by using quantum corrections in Nieh–Yan (NY) modified Einstein-Cartan (EC) gravity with the Holst term. The reason why we introduce some extra terms in the actions, is that even when one adds both NY and Holst terms, being topological terms, they do not contribute to the dynamics of the problem and to the equations of motion (EOM). Examples run from quantum corrections and torsion mass in the dark universe with very light inflaton approximation to bouncing cosmologies in NY gravity. This follows similar model from Tukhashvili and Steinhardt (2023) of a bouncing cosmology induced by torsion condensates in EC gravity. The Lagrangian in this paper, is shown to be expressed in terms of NY polynomial form. The quantum one-loop correction is taken in NY Lagrangian as the inverse of BI parameter. This has been recently appeared in He et al. (2024) quantum corrections in Einstein-Cartan-Nieh–Yan one loop quantum gravity in Starobinsky inflation. We show that to have a cosmological NY dark universe one needs a real BI parameter. Inflation Hubble scale of the order of O(100eV) and very light inflaton of mass ∼10−12TeV are used due to its relation with dark matter. The very light mass character of inflatons and much heavier torsion are responsible to induced cosmological bounce in dark universe. When one introduces the quantum correction parameter b as second-order in front of the NY topological term in squared and introduce the NY term back into the ECH gravity, the EC gravity limit where BI parameter β→∞, yields a chiral fermion density ρ5. This result lies very close to the upper bound in the range of 0≤β≤1.185, previously obtained by Panza et al. Analysis of fermionic currents shows that Holst term can be eliminated by choosing β=0.288. Massive torsion oscillates in Einstein-Cartan gravity in the BI limit of β→∞.

A coupled-fluid approach to explore bounce and inflationary cosmology with Barrow holographic as the driving dark fluid

Assuming that viscous fluid in the form of Barrow holographic dark energy (BHDE) (a particular case of more generalized version of HDE elaborated in Nojiri et al. in Phys Lett B 825:136844, 2022; Symmetry 13(6):928, 2021) and pressure-less dark matter are present across the flat Friedmann–Robertson–Walker universe, we find the precise solutions of viscous BHDE models in non-interacting and interacting scenarios for different choices of scale factor. We show the evolution of the EoS parameters in the viscous non-interacting and interacting situations together with the deceleration parameters for observing the transition time frame. Afterwards, we investigate a bounce inflation model using the analytical results of model’s slow-roll parameters, scalar spectral index, and tensor-to-scalar ratio. We investigated an association between BHDE and scalar field models since inflation is typically attributed to the existence of scalar fields. The evolution of the generated potential from the scalar fields are plotted against time. Finally, we investigated the GSL of the thermodynamics.

Little rip, pseudo rip and bounce cosmology with generalized equation of state in non-standard backgrounds

The discovery of universe’s late-time acceleration and dark energy has overseen a great deal of research into cosmological singularities and particularly future singularities. Perhaps the most extreme of such singlarities is the big rip, which has propelled a lot of work into ways of moderating it or seeking out alternatives to it and two such alternatives to the big rip are the Little rip and Pseudo rip. Another possibility to consider the far future of the universe is through bounce cosmologies, which presents its own interesting ideas. So in this work we investigate the Little rip, Pseudo rip and Bounce cosmology in non-standard cosmological backgrounds with a generalized equation of state in the presence of a viscous fluid. In particular we discuss about Chern-Simons cosmology and the RS-II Braneworld and discuss how the exotic and non-conventional nature of gravity in such cosmologies affect universal evolution in these scenarios. We find out that there are very significant differences in the behaviour of such cosmic scenarios in these universes in comparison to how they appear in the simple general relativistic universe.