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arxiv: 2108.09524 · v3 · pith:7L45ZXPQnew · submitted 2021-08-21 · 🌀 gr-qc · astro-ph.CO· hep-th

Classical and Semiclassical Stability of Emergent Universes in Jordan-Brans-Dicke Theory

Pedro Labra\~na , Juan Ortiz This is my paper

Pith reviewed 2026-05-24 13:37 UTC · model grok-4.3

classification 🌀 gr-qc astro-ph.COhep-th
keywords Jordan-Brans-Dicke theoryemergent universeEinstein static statesemiclassical tunnelingWheeler-DeWitt equationclassical stabilityminisuperspace
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The pith

In Jordan-Brans-Dicke theory the Einstein static state resists both classical perturbations and specific semiclassical tunneling for suitable potentials and parameters.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper investigates the stability of the past-eternal Einstein static state that serves as the starting point in the emergent universe scenario, now placed inside Jordan-Brans-Dicke scalar-tensor gravity. It examines both linear classical perturbations around that state and the shape of the Wheeler-DeWitt potential that controls semiclassical tunneling to configurations with vanishing scale factor. For particular choices of the scalar potential and the theory parameters the static state remains an extremum with a positive barrier against the tunneling channels that respect the Hamiltonian constraint. This construction supplies a nonsingular, geodesically complete cosmological history that avoids the quantum decay channel identified in earlier work.

Core claim

The authors show that the Einstein static configuration in Jordan-Brans-Dicke theory can be rendered classically stable and protected from the representative semiclassical tunneling processes compatible with the Hamiltonian constraint by selecting appropriate forms of the JBD potential and suitable values of the model parameters.

What carries the argument

The Wheeler-DeWitt potential in minisuperspace, whose barrier height and shape determine whether tunneling from the Einstein static state to zero scale factor is suppressed.

If this is right

  • The emergent universe can begin from a classically and semiclassically stable Einstein static state inside Jordan-Brans-Dicke theory.
  • Quantum decay to zero scale factor is blocked for the analyzed tunneling channels when the potential and parameters are chosen appropriately.
  • Classical stability of the static solution is compatible with semiclassical protection in the same models.
  • Regions of parameter space exist where the Einstein static state does not suffer the instability discussed in prior literature.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Analogous stability might be achievable in other scalar-tensor theories if their potentials are tuned in a similar way.
  • The allowed parameter ranges could be confronted with observational bounds on the Brans-Dicke coupling.
  • A complete treatment would need to check whether additional tunneling channels beyond the Hamiltonian-constraint subset can still destabilize the state.

Load-bearing premise

The semiclassical analysis considers only representative tunneling channels that satisfy the Hamiltonian constraint and leaves other possible quantum processes unexamined.

What would settle it

Explicit construction of a JBD potential and parameter set for which the Wheeler-DeWitt equation admits a non-negligible tunneling amplitude from the Einstein static state to vanishing scale factor would falsify the claimed robustness.

Figures

Figures reproduced from arXiv: 2108.09524 by Juan Ortiz, Pedro Labra\~na.

Figure 1
Figure 1. Figure 1: FIG. 1: The pltos were obtained by using the Brans-Dicke potential in Eq. (47), considering [PITH_FULL_IMAGE:figures/full_fig_p010_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2: The plots were obtained by using the Brans-Dicke potential in Eq. (47), considering [PITH_FULL_IMAGE:figures/full_fig_p010_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: The plts were obtained by using the Brans-Dicke potential (48) considering [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: The plots were obtained by using the Brans-Dicke potential (48), considering [PITH_FULL_IMAGE:figures/full_fig_p012_4.png] view at source ↗
read the original abstract

The Emergent Universe scenario is based on the assumption that the universe originates from a past-eternal Einstein static (ES) state, subsequently evolving toward an inflationary phase and a hot Big Bang era. Such models are appealing as they provide nonsingular and geodesically complete cosmological histories. However, it has been argued by Mithani and Vilenkin that, even when the ES state is classically stable, certain models can admit semiclassical tunneling channels leading to quantum decay toward configurations of vanishing scale factor. In this work, we investigate the classical and semiclassical stability of the ES regime in the context of Jordan-Brans-Dicke (JBD) theory. We analyze the structure of the Wheeler-DeWitt potential in minisuperspace and study representative semiclassical tunneling channels compatible with the Hamiltonian constraint. We show that, for suitable choices of the JBD potential and model parameters, the ES configuration can be robust against both classical perturbations and the semiclassical tunneling processes considered here. Our results indicate that the quantum instability discussed by Mithani and Vilenkin may be avoided within certain regions of parameter space, while leaving open the possibility of more general tunneling processes beyond the scope of the present analysis.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The paper investigates the classical and semiclassical stability of the Einstein static (ES) state in Jordan-Brans-Dicke (JBD) theory as a foundation for the emergent universe scenario. Using minisuperspace Wheeler-DeWitt methods, it analyzes the structure of the Wheeler-DeWitt potential and representative tunneling channels compatible with the Hamiltonian constraint. The central claim is that, for suitable choices of the JBD potential and model parameters, the ES configuration is robust against classical perturbations and the specific semiclassical tunneling processes considered, potentially avoiding the quantum decay to vanishing scale factor identified by Mithani and Vilenkin, while noting that more general tunneling channels lie outside the analysis scope.

Significance. If the result holds with explicit support, the work would be significant for quantum cosmology by showing that JBD theory can stabilize emergent universe models against the semiclassical instability of Mithani and Vilenkin within restricted but representative channels. The application of standard Wheeler-DeWitt techniques to this modified-gravity setting is a strength, and the qualified scope of the tunneling analysis prevents overclaiming completeness.

major comments (1)
  1. [Abstract] Abstract: the central claim that the ES configuration 'can be robust against both classical perturbations and the semiclassical tunneling processes considered here' for 'suitable choices of the JBD potential and model parameters' is asserted without supplying explicit potential forms, parameter values, or numerical evidence of the resulting Wheeler-DeWitt potential barriers in the abstract; if the results sections do not contain concrete derivations or examples demonstrating stability, the support for the claim cannot be verified from the text.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their detailed review and constructive feedback on our manuscript. We address the single major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the central claim that the ES configuration 'can be robust against both classical perturbations and the semiclassical tunneling processes considered here' for 'suitable choices of the JBD potential and model parameters' is asserted without supplying explicit potential forms, parameter values, or numerical evidence of the resulting Wheeler-DeWitt potential barriers in the abstract; if the results sections do not contain concrete derivations or examples demonstrating stability, the support for the claim cannot be verified from the text.

    Authors: The results sections (particularly Sections 3 and 4) contain explicit forms of the JBD potential, specific parameter values, and derivations of the Wheeler-DeWitt potential, including the structure of barriers that demonstrate classical and semiclassical stability for those choices. The abstract is written in the standard concise style and summarizes the outcome of those calculations without repeating the explicit forms. If the referee finds the abstract insufficiently indicative, we are willing to add a brief clause referencing the existence of such explicit examples in the body. revision: partial

Circularity Check

0 steps flagged

No significant circularity identified

full rationale

The paper applies standard Wheeler-DeWitt minisuperspace methods to analyze classical perturbations and specific semiclassical tunneling channels in JBD theory for the emergent universe ES state. The central claims are explicitly restricted to the representative channels compatible with the Hamiltonian constraint, with open acknowledgment that more general processes lie outside scope. No derivations reduce to self-definitions, fitted inputs renamed as predictions, or load-bearing self-citations; the analysis references external work (Mithani-Vilenkin) as motivation without importing uniqueness theorems or ansatze from the authors' prior papers. The derivation chain is self-contained against external benchmarks and does not exhibit any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim depends on the existence of suitable JBD potentials and on the minisuperspace reduction being sufficient to capture the relevant tunneling dynamics.

free parameters (1)
  • JBD potential parameters
    Suitable choices are required to achieve robustness of the ES state.
axioms (1)
  • domain assumption Minisuperspace approximation
    Used to construct and analyze the Wheeler-DeWitt potential.

pith-pipeline@v0.9.0 · 5746 in / 1147 out tokens · 27265 ms · 2026-05-24T13:37:41.604034+00:00 · methodology

discussion (0)

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Reference graph

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