Bouncing Cosmology and the Early Universe: From Theory to Observations

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Cosmology".

Deadline for manuscript submissions: 31 May 2026 | Viewed by 2754

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Interests: particle physics; high-energy physics; high-energy physics theory; theoretical high-energy physics; astroparticle physics; fundamental physics; theoretical particle physics; field theory
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Dear Colleagues,

Bouncing cosmology offers an alternative to the Big Bang by positing cyclic phases of contraction and expansion, avoiding singularities. Theoretical advances, such as loop quantum cosmology and \(f(R)\) gravity, provide mechanisms for a smooth bounce via quantum corrections and higher-order modifications. Ekpyrotic models using scalar fields address issues such as anisotropy, enhancing the plausibility of these scenarios.

Observations from the CMB and large-scale structure constrain bouncing cosmologies. Features such as suppressed power at large scales and specific non-Gaussian patterns could distinguish these models from inflationary paradigms. Data from Planck and BICEP/Keck collaborations already support aspects of certain bounce models. Upcoming missions, such as LiteBIRD, aim to refine these constraints further, testing the models' predictions against inflation.

Bouncing cosmology also connects with broader early-universe phenomena. Mechanisms for pre-bounce baryogenesis offer solutions to the matter–antimatter asymmetry. Links between bouncing models and late-time observations, such as cosmic acceleration and primordial string remnants, suggest a potential to address dark energy and dark matter within this framework. These developments demonstrate the potential of bouncing cosmology as a compelling alternative framework for understanding the universe’s origins.

Dr. Arnab Dasgupta
Guest Editor

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Keywords

  • bouncing cosmology
  • cyclic universe
  • cosmic microwave background (CMB)
  • matter–antimatter asymmetry
  • dark energy and dark matter

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Published Papers (2 papers)

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Research

10 pages, 1152 KB  
Article
Logamediate Warm Axion Inflation in Light of Planck Data
by Zahra Shamloui, Vahid Kamali and Saeid Ebrahimi
Universe 2025, 11(12), 410; https://doi.org/10.3390/universe11120410 - 10 Dec 2025
Viewed by 101
Abstract
Axion warm inflation is studied within the framework of Logamediate inflation. Using a novel approach, we constrain the parameter space of the model and find a reasonable region of free parameters compatible with the temperature, polarization, and lensing CMB data. We focus on [...] Read more.
Axion warm inflation is studied within the framework of Logamediate inflation. Using a novel approach, we constrain the parameter space of the model and find a reasonable region of free parameters compatible with the temperature, polarization, and lensing CMB data. We focus on an inflaton evolution characterized by a high dissipative regime, where particle production impacts the inflaton dynamics more than the expansion rate. Specifically, we consider the cubic form of the dissipation coefficient, Υ=Υ0T3, as proposed in minimal warm inflation. We show that this parameter remains large during the slow-roll epoch for a broad range of the free parameter Υ0, as indicated by our data analysis. Full article
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14 pages, 933 KB  
Article
Evolution of the Early Universe in Einstein–Cartan Theory
by Qihong Huang, He Huang, Bing Xu and Kaituo Zhang
Universe 2025, 11(5), 147; https://doi.org/10.3390/universe11050147 - 2 May 2025
Cited by 3 | Viewed by 1515
Abstract
Einstein–Cartan theory is a generalization of general relativity that introduces spacetime torsion. In this paper, we perform phase space analysis to investigate the evolution of the early universe in Einstein–Cartan theory. By studying the stability of critical points in the dynamical system, we [...] Read more.
Einstein–Cartan theory is a generalization of general relativity that introduces spacetime torsion. In this paper, we perform phase space analysis to investigate the evolution of the early universe in Einstein–Cartan theory. By studying the stability of critical points in the dynamical system, we find that there exist two stable critical points which represent an Einstein static solution and an expanding solution, respectively. After analyzing the phase diagram of the dynamical system, we find that the early universe may exhibit an Einstein static state, an oscillating state, or a bouncing state. By assuming the equation of state ω can decrease over time t, the universe can depart from the initial Einstein static state, oscillating state, or bouncing state and then evolve into an inflationary phase. Then, we analyze four different inflationary evolution cases in Einstein–Cartan theory and find that a time-variable equation of state ω cannot yield values of ns and r consistent with observations, while a time-invariant equation of state ω is supported by the Planck 2018 results. Thus, in Einstein–Cartan theory, the universe likely originates from a bouncing state rather than an Einstein static state or an oscillating state. Full article
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