The phantom menaced: constraints on low-energy effective ghosts

Guy D. Moore; James M. Cline; Sangyong Jeon

REVIEW

The phantom menaced: constraints on low-energy effective ghosts

James M. Cline, Sangyong Jeon, Guy D. Moore

High Energy Physics - Phenomenology · Submitted 24 Nov 2003 · 12 references

Pith's verdict: The Λ ≲ 3 MeV bound is a real, robust result; the soft spots are the EGRET extrapolation (weakly leveraged) and the asserted Fig. 2 cancellation (argued, not computed).

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arXiv IDhep-ph/0311312 (version 4)

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CitationGuy D. Moore, James M. Cline, Sangyong Jeon. "The phantom menaced: constraints on low-energy effective ghosts." arXiv:hep-ph/0311312 (2003). https://pith.science/paper/WUG3B554

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Editor's note

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Worth your time, and worth citing. The core of this one is a clean, model-independent observation: a wrong-sign kinetic term coupled only gravitationally still gives vacuum → 2γ2φ at a rate ~ Λ^8/M_p^4 (Eq. 3), and comparing the resulting diffuse photon flux to EGRET caps the Lorentz-violating cutoff at Λ ≲ 3 MeV. That is a genuinely new number relative to the phantom literature, and it does real damage to the idea that ghosts come from anywhere near the TeV scale. The eighth-root scaling is the reason to trust it: even a factor-100 error in the assumed flux at a few MeV only moves 3 MeV to about 5 MeV. The Lorentz-conserving chain in Eq. 9 is cruder — a formation-time cutoff θ(t0 − k0/k2) — but it is presented as the conservative case, and the conclusion (Λ ≲ 1 meV, gravity modified above 0.2 mm, excluded by torsion balance) follows from it. The correction of Carroll-Hoffman-Trodden is also useful: the point that their φ → gφφ rate is an artifact of noncanonical normalization is right, and the time-dilation criticism of at-rest decay rates is right too. The authors are upfront in the Remarks that Lorentz violation is required and that this sits badly with general covariance; that is acknowledged, not a new finding, so don't hold it against them twice. On soft spots: the EGRET extrapolation from E0 = 451 MeV down to a few MeV is real, but the reader overweights it — the eighth root blunts it, and the paper's flat-spectrum assumption below Λ is the natural one for a four-body phase space cut off at Λ. The more load-bearing soft spot for the paper's rhetoric is Fig. 2: the claim that the φ → gφφ amplitude cancels among the contact term and three other diagrams is asserted diagrammatically, with no vertex factors or symmetry argument. If that cancellation fails, the improvement over ref. [6] is less clean — though the 3 MeV bound itself does not depend on it. That is a paragraph-level gap, not a load-bearing flaw. Audience: anyone working on phantom dark energy, Lorentz violation in gravity, or vacuum stability in effective theories. It deserves a serious referee, mainly to make them write out the Fig. 2 cancellation explicitly.

Referee report

Significance

If correct, the result is a strong and essentially model-independent constraint on a widely discussed dark-energy proposal: it uses only minimal gravitational coupling, requires no knowledge of the ghost potential, and produces a falsifiable number. The Lorentz-invariant no-go is a clean and useful statement. The paper is appropriately explicit that Eq. (3) is a dimensional estimate and that the bound depends only on gravitational coupling, and the field-redefinition argument against ref. [6] is a genuine correction to the literature. The main observational input, however, is an extrapolation of the EGRET power law, and the exclusion of Lorentz-invariant ghosts rests on an unstated assumption about the universality of the cutoff; both should be made explicit.

Major objections (3)

[Eqs. (6)-(8)] The bound Λ ≲ 3 MeV compares the predicted flux at E ~ Λ ~ 3 MeV with the EGRET fit Eq. (7), which is quoted at E0 = 451 MeV. This is roughly two orders of magnitude below the reference energy and below the band EGRET actually measured. The manuscript should state the energy range over which Eq. (7) was fitted and should say explicitly that the bound assumes the power law continues down to a few MeV. The concern is real but weakly leveraged: combining Λ^7 from Eq. (6) with E^-2.1 from Eq. (7) evaluated at E ~ Λ gives Λ ∝ (flux)^{1/9.1}, so even a factor-100 error in the assumed flux at 3 MeV shifts Λ by only about 1.7. A sentence quantifying this, and ideally a cross-check against a direct few-MeV measurement such as COMPTEL, would make the headline number defensible.
[Abstract, Eq. (9), and the paragraph beginning ``If we demand Lorentz invariance''] The exclusion of Lorentz-conserving ghosts (abstract:s4) rests on the step ``Gravity would receive order 1 modifications at a length scale > 0.2 millimeters.'' That step assumes the cutoff Λ applies universally, including to the graviton sector. If the cutoff is a ghost-sector-only regulator (for instance a dispersion-based or Pauli-Villars cutoff acting only on ghost modes), the 0.2 mm torsion-balance constraint need not apply, and the exclusion of Lorentz-invariant ghosts would not follow. The manuscript should state this assumption explicitly and justify it, or weaken the claim from ``completely excluded'' to ``excluded under the assumption that the cutoff is universal.''
[Fig. 2 and the paragraph rebutting ref. [6]] The assertion that the φ → gφφ amplitude vanishes by cancellation among the contact term and three other diagrams is argued diagrammatically, without explicit vertex factors or a symmetry argument. Because this is a claim that a published bound is incorrect, it should be supported by an explicit calculation, or at least by the on-shell Ward identity that enforces the cancellation. The same field-redefinition argument that removes the φ g^{μν} ∂_μ φ ∂_ν φ vertex should also be reconciled with the survival of the 0 → 2γ2φ amplitude used in Eq. (3): the manuscript should state why the graviton-ghost coupling in Eq. (3) is physical (the ghost stress tensor) while the vertex in Fig. 2 is not. This does not affect Eq. (8), but it is a substantive claim about the literature.

Minor objections (6)

[Eq. (5)] The statement that ``Most of the photon pairs have been produced since redshift z = 1'' should be justified. For matter domination n ∝ t, so the fraction produced since z = 1 is about 1 − (1+z)^{-3/2} ≈ 0.64; a sentence showing this would make the claim transparent.
[Eq. (6)] The predicted spectrum is taken flat below Λ, whereas the actual four-body phase space is not flat. The manuscript should note that this is a rough approximation and that it affects the comparison at the factor-of-a-few level, which is harmless given the weak leverage of the bound.
[Paragraph on e+e− production] The constraint Λ ≲ 40 MeV from excessive rescattering of the microwave sky is quoted without derivation. The manuscript should either sketch the argument or cite a source for it.
[Ref. [9] and the UHECR bound] The statement ``less than 1 event per km^2 per century [9]'' cites the HIRES/Fly's Eye papers, which report the cosmic-ray spectrum rather than a flux limit at the relevant energy. The manuscript should confirm that ref. [9] supports this specific number or cite a more appropriate ultra-high-energy cosmic-ray flux limit.
[Eq. (9)] The powers of Λ and t0 in Γ ~ Λ^10 t0^2/M_p^4 are not transparent from the displayed integral, and the final 1 meV bound depends on them. A brief derivation, or a statement that the result is schematic up to O(1) factors, would help the reader.
[Eq. (6) and the surrounding discussion] Photons produced at z ~ 1 are redshifted before reaching the Earth, so the spectrum today is shifted relative to the production spectrum. For E ~ Λ this is a factor of about two and does not affect the conclusion, but a sentence acknowledging it would be appropriate.

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The paper

The paper claims

Phantom dark energy, the kind with negative kinetic energy, would make the vacuum decay into gamma rays unless its high-energy cutoff sits below about 3 MeV.

The reading

A scalar field with the wrong-sign kinetic energy — a 'ghost' or phantom field — is one candidate explanation for the observed late-time acceleration of the universe. The trouble is that such a field makes the vacuum unstable: graviton exchange lets the vacuum spontaneously produce two ghosts and two photons, with a rate that grows like the eighth power of the cutoff, $Γ ∼ Λ^8/M_p^4$. The authors ask how low that cutoff must be for the resulting photon bath to have escaped notice, and answer by comparing the predicted diffuse gamma-ray spectrum with the measured extragalactic background. They find $Λ ≲ 3$ MeV, and further show that if the cutoff respects Lorentz invariance the required value is so low that it would already have shown up as a deviation from Newtonian gravity at sub-millimeter distances. The upshot is that phantom dark energy, if it exists at all, must come from new physics far below the TeV scale and must break Lorentz symmetry.

What carries the argument

The load-bearing object is the vacuum decay rate $Γ_{0→2γ2φ} ∼ Λ^8/M_p^4$, obtained on dimensional grounds from the graviton-exchange diagram with two ghost and two photon legs, together with the cosmological evolution equation $d(a^3 n)/dt = a^3 Γ$ that converts a rate per spacetime volume into a present-day number density. Because the rate is so steep in $Λ$, the comparison with the EGRET differential flux $dF/dE = 7.3×10^{-9}(E/E_0)^{-2.1}$ (cm$^2$ s sr MeV)$^{-1}$ at $E_0 = 451$ MeV translates into a numerically tight ceiling on the cutoff. The second piece of machinery is the frame-dependence argument: a Lorentz-invariant cutoff on the virtual graviton's invariant mass still leaves a divergent integral over boosts, so only a Lorentz-violating cutoff renders the rate finite; imposing Lorentz invariance instead forces a formation-time restriction $γ < t_0√s$ that pushes the bound to the milli-electron-volt scale.

Extended reading notes

Core claim

The paper's central claim is a phenomenological bound rather than a model: any low-energy effective theory containing a canonical wrong-sign scalar must impose a Lorentz-violating momentum cutoff $Λ ≲ 3$ MeV on the final-state phase space of the graviton-mediated process $0 → 2γ2φ$. The argument is that the production rate scales as $Λ^8/M_p^4$, so the accumulated photon density today is roughly $Γ$ times the age of the universe, with a spectrum that is flat below $E ∼ Λ$ and peaks near $Λ$. Comparing $dn/dE ∼ Λ^7 M_p^{-4} t_0$ against the diffuse gamma-ray flux measured by EGRET forces the cutoff down to the few-MeV scale. Because the required cutoff singles out a preferred frame — naturally the cosmic microwave background rest frame — the theory cannot be made generally covariant. If one instead insists on a Lorentz-invariant cutoff, the authors estimate $Λ ≲ 1$ meV, which would mean order-one modifications of gravity at lengths above about 0.2 mm, already excluded by torsion-balance tests. Along the way the paper corrects an earlier bound: the amplitude for a ghost to decay into a graviton and two ghosts cancels to zero, so the previously quoted limits based on that channel do not apply.

Load-bearing premise

The 3 MeV number assumes the EGRET power-law flux, quoted at 451 MeV, continues unchanged down to a few MeV, roughly a hundred times lower in energy and outside the band where it was measured.

Editorial extensions

If this is right

Any phantom-dark-energy model must be embedded in a theory whose ultraviolet completion breaks Lorentz invariance below the MeV scale, which rules out string theory or any TeV-scale completion as its source.
The ghost sector must be essentially hidden from the Standard Model, communicating only gravitationally, since any additional coupling would strengthen the gamma-ray bound.
The bound is insensitive to the ghost potential and holds for any ghost mass below $Λ$, so the $10^{-33}$ eV masses typical of phantom cosmology are comfortably allowed.
Production of electron-positron pairs rather than photons gives a weaker but independent constraint, $Λ ≲ 40$ MeV, from rescattering of the microwave background by an intergalactic plasma.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

The bound is a statement about the cutoff, not about the ghost's existence, so it can be read in reverse: a future MeV-band gamma-ray telescope measuring a diffuse flux well below the extrapolated EGRET power law would loosen the ceiling proportionally, while a MeV excess would tighten it sharply.
Because the required Lorentz violation is communicated to ordinary matter through graviton loops, the same MeV-scale cutoff could in principle leave correlated imprints in precision tests of Lorentz invariance in particle physics, which would be a sharper probe than the gamma-ray flux alone.
The paper's correction of the earlier decay-channel bound suggests a general lesson: for theories with derivative couplings, at-rest decay rates can be artifacts of field normalization, and phase-space-integrated production rates are the safer diagnostic.
If ghosts are excluded, the remaining explanations for acceleration must either be a cosmological constant or a Lorentz-respecting scalar, so the argument indirectly strengthens the case for accepting a small vacuum energy rather than engineering it away.

Original abstract

It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum. We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff Lambda which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels. Assuming only that ghosts interact at least gravitationally, we show that Lambda < 3 MeV for consistency with the cosmic gamma ray background. We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded.

The compiled record

The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.

Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,223 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.04 · states limitation 0.42 · human participants 0.01 · controlled comparison 0.03 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.14 · mentions code or data availability 0.02.

The abstract, sentence by sentence

arXiv listing abstract v4. Results and the main claim are underlined; show every role.

It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration. Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum. We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff Lambda which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels. Assuming only that ghosts interact at least gravitationally, we show that Lambda < 3 MeV for consistency with the cosmic gamma ray background. We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	It has been suggested that a scalar field with negative kinetic energy, or ``ghost,'' could be the source of the observed late-time cosmological acceleration.	background 1.00	0.03	0.03	hedged possibility 1.00
s1	Naively, such theories should be ruled out by the catastrophic quantum instability of the vacuum.	background 0.99	0.04	0.03	hedged possibility 0.59
s2	We derive phenomenological bounds on the Lorentz-violating ultraviolet cutoff Lambda which must apply to low-energy effective theories of ghosts, in order to keep the instability at unobservable levels.	contribution 0.97	0.96	0.22	asserted 0.97
s3	Assuming only that ghosts interact at least gravitationally, we show that Lambda < 3 MeV for consistency with the cosmic gamma ray background.	result 1.00	0.94	0.68	asserted 0.98
s4	We also show that theories of ghosts with a Lorentz-conserving cutoff are completely excluded.	result 1.00	0.94	0.23	asserted 1.00

What kind of paper the classifier reports this is: theoretical result 1.00 · evidence from proof or derivation 0.99.

What was examined, and what was not

sources read

arXiv listing abstract v4

not examined

full text
figures and tables
references and citing sentences
relations to other papers

levels run

P abstract

not run

S sections
T body sentences
C citations
R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

Figures

**Figure 1.** Graviton-mediated decay of vacuum into two ghosts and two photons. An implicit excuse for even considering phantom matter at the classical level is perhaps the idea that, at long distances, the scalar field theory is merely an effective one, whose ultraviolet completion is well defined and respects unitarity. In this way, it might be possible to have a physical value for the cutoff in (3) which was small enough so that the rate of decay of the vacuum is slow on cosmological time scales. In this letter, we estimate just how low a cutoff Λ is required for consistency with…

**Figure 2.** Vanishing of the amplitude for a ghost to decay into graviton and two ghosts. Remarks. The stringent limit we have obtained from the diffuse gamma ray background, Λ <∼ 3 MeV, implies that any theory of low-energy effective ghosts must originate from new physics far below the TeV scale. Therefore we cannot invoke string theory, for example, as a plausible source for effective ghosts. Instead, we must imagine that they come from a low-energy sector that is completely hidden from the standard model, except for gravitational couplings. This makes ghosts look even more unlikely, in our

Figures reproduced from arXiv:hep-ph/0311312 by the authors.

References

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A non-local theory of massive gravity
hep-th 2013-05 conditional novelty 6.0 of 10

A covariant non-local massive gravity theory is constructed whose scalar ghost has mass equal to the graviton mass and decouples as m goes to zero, making its vacuum instability negligible for m of order H0.
Subluminal Galilean Genesis
hep-th 2012-09 conditional novelty 6.0 of 10

Adding a conformal-breaking quartic term to the Galilean Genesis Lagrangian yields a stable, null-energy-condition-violating background whose perturbations travel well below the speed of light.
The Effective Theory of Quintessence: the w<-1 Side Unveiled
astro-ph 2008-11 accept novelty 6.0 of 10

Dark energy with w < -1, and dark energy crossing w = -1, are not generically pathological; stability only requires the sound speed to be essentially zero on cosmological scales.
Ghosts, Instabilities, and Superluminal Propagation in Modified Gravity Models
astro-ph 2006-04 conditional novelty 6.0 of 10

In the CDDETT modified gravity model, late-time accelerating attractor solutions generically have superluminal tensor or scalar propagation, even when fourth-order derivative ghosts are absent.
Could dark energy be vector-like?
astro-ph 2004-05 conditional novelty 6.0 of 10

A set of three orthogonal vector fields with a tachyonic self-interaction can act as dark energy, reaching an equation of state below minus one with a conventional kinetic term, and it violates the scalar/vector/tenso...
Observational constraints on scalar-vector-tensor dark energy with phantom-divide crossing
astro-ph.CO 2026-09 conditional novelty 5.0 of 10

Current supernova, BAO, compressed CMB, and growth data are consistent with a stable phantom-divide crossing in a scalar-vector-tensor dark-energy model, with Bayes factors of 2 to 13 over flat LambdaCDM depending on ...
A Friendly Phantom: Late-time AdS-to-dS transition and cosmological tensions
gr-qc 2026-06 unverdicted novelty 5.0 of 10

Ph-Λ_sCDM realizes sign-switching dark energy via a phantom scalar on a tanh potential, enabling controlled AdS-to-dS transition without Big Rip.
Endpoint Logarithms in the NLO Mueller-Navelet Jet Vertex: Threshold Matching and BLM/MOM Prescription Sensitivity
hep-ph 2026-06 unverdicted novelty 5.0 of 10

A conservative BFKL-aware threshold matching scheme is constructed for the NLO forward jet vertex that resums ordinary endpoint logs, preserves NLO accuracy, and is tested against CMS azimuthal observables, showing in...
About electroweak domain walls in Majoron models
hep-ph 2025-06 conditional novelty 5.0 of 10

Electroweak instantons alone do not produce Majoron domain walls; a tiny instanton mass from B+L breaking is cosmologically negligible and can act as a bias or dark energy.
DHOST Bounce
gr-qc 2020-02 conditional novelty 5.0 of 10

Adding DHOST operators to a Horndeski bounce lifts the scalar sound speed above zero through the bounce, evading the no-go theorem for nonsingular cosmologies in Horndeski/Galileon theories.
de Sitter Swampland, $H_0$ tension & observation
hep-th 2018-07 conditional novelty 5.0 of 10

A two-parameter holographic dark energy model fits low-redshift H(z) data with a high H0 and predicts a turning point in H(z) at z* about 0.07, a feature low-z surveys can test.
Finite Conformal Quantum Gravity and Nonsingular Spacetimes
hep-th 2016-05 conditional novelty 5.0 of 10

Finite non-local quantum gravity is shown to be anomaly-free conformal gravity in a spontaneously broken phase, and conformal transformations map singular Schwarzschild, FRW, and BKL spacetimes to regular ones.
Aspects of Quadratic Gravity
hep-th 2015-05 conditional novelty 5.0 of 10

Pure R^2 gravity propagates only a massless scalar on flat space, with the graviton returning on curved backgrounds or when an Einstein term is added, and a string compactification is proposed as a UV origin.
Towards Anisotropy-Free and Non-Singular Bounce Cosmology with Scale-invariant Perturbations
astro-ph.CO 2013-03 conditional novelty 5.0 of 10

A ghost-free Galileon bounce with an Ekpyrotic-like negative potential gives w > 1 in contraction (suppressing anisotropy), and a coupled curvaton field supplies the nearly scale-invariant spectrum, with a reconstruct...
A Matter Bounce By Means of Ghost Condensation
hep-th 2010-07 conditional novelty 5.0 of 10

A ghost-condensate scalar field with a hand-chosen inverse-power potential yields a non-singular matter bounce whose observable-scale perturbations survive the bounce.
Non-singular cosmology in a model of non-relativistic gravity
hep-th 2009-06 conditional novelty 5.0 of 10

In a non-relativistic, power-counting renormalizable gravity model, a negative-energy 'dark radiation' term sourced by spatial curvature can replace the big bang singularity with a bounce and support a cyclic universe.
A Nonsingular Cosmology with a Scale-Invariant Spectrum of Cosmological Perturbations from Lee-Wick Theory
hep-th 2008-10 conditional novelty 5.0 of 10

In a Lee-Wick two-scalar cosmology, a nonsingular bounce converts vacuum fluctuations from a matter-dominated contracting phase into a scale-invariant spectrum of metric perturbations, without inflation.
k-Essence, superluminal propagation, causality and emergent geometry
hep-th 2007-08 conditional novelty 5.0 of 10

Superluminal sound speeds in k-essence do not produce closed causal curves on homogeneous, Friedmann, or black-hole accretion backgrounds, because a global time function still exists for the effective acoustic metric.
Quintom Model Perturbations
astro-ph.CO 2026-06 unverdicted novelty 4.0 of 10

A two-field quintom model reproduces w0waCDM perturbation features and is mildly favored over it in Bayesian fits to BAO, CMB, and SNIa data.
The Generalized Second Law and the Spatial Curvature Index
gr-qc 2025-10 unverdicted novelty 4.0 of 10

Generalized second law on the apparent horizon plus w ≥ -1 and the dominant energy condition rules out hyperbolic spatial sections for homogeneous isotropic universes.
Extended Dark Energy analysis using DESI DR2 BAO measurements
astro-ph.CO 2025-03 conditional novelty 4.0 of 10

Extended analysis of DESI DR2 data confirms robust evidence for dynamical dark energy with phantom crossing preference, stable under parametric and non-parametric modeling.
Quintom cosmology and modified gravity after DESI 2024
astro-ph.CO 2024-04 conditional novelty 4.0 of 10

A Gaussian-process reconstruction of the BAO expansion history yields a phantom-to-quintessence crossing of the dark-energy equation of state at 0.78 to 0.93 sigma, and the same expansion history is inverted into quad...
Quintessential interpretation of the evolving dark energy in light of DESI
astro-ph.CO 2024-04 conditional novelty 4.0 of 10

A canonical quintessence field can reproduce the DESI preference for evolving dark energy over the observed redshift range, with the phantom crossing falling beyond the pivot redshift where the data are most constraining.
Dynamics with Infinitely Many Derivatives: The Initial Value Problem
hep-th 2007-09 conditional novelty 4.0 of 10

Infinite-order field equations require two initial data per propagator pole, and a contour choice can remove ghost poles from p-adic and string field theory, at the cost of an ad hoc redefinition.
Effective Phantom Dark Energy: What Cosmological Reconstruction Does and Does Not Imply
astro-ph.CO 2026-05 unverdicted novelty 3.0 of 10

Effective phantom dark energy is a background-level reconstruction that does not imply fundamental pathologies such as ghost instabilities or null energy condition violation by the underlying stress tensor.
The Quintom theory of dark energy after DESI DR2
astro-ph.CO 2025-05 unverdicted novelty 3.0 of 10

This review traces the history of dynamical dark energy, presents the no-go theorem against single-field crossing of w = -1, and surveys viable Quintom constructions including multi-field models and modified gravity i...
Weakly-Coupled Trace Anomaly Action for Gravity
hep-th 2025-05 conditional novelty 3.0 of 10

The trace anomaly effective action for gravity is not a valid low-energy EFT unless a new sector with spontaneously broken scale invariance adds a kinetic term for the anomalyon scalar.
Effective Field Theory of Dark Energy: a Review
astro-ph.CO 2019-07 accept novelty 3.0 of 10

The review consolidates the effective field theory of dark energy: its action, its mapping onto known gravity theories, its stability conditions, and the cosmological constraints and forecasts obtained with it.
Dynamical systems applied to cosmology: dark energy and modified gravity
gr-qc 2017-12 accept novelty 3.0 of 10

A comprehensive review that catalogues fixed points and stability conditions for roughly a hundred dark-energy and modified-gravity cosmologies, ruling some out on purely theoretical grounds and flagging others for ob...
A Critical Review of Classical Bouncing Cosmologies
astro-ph.CO 2014-06 accept novelty 3.0 of 10

Most bouncing cosmologies do not yet match current data or avoid known instabilities, but a few, notably the super-bounce and S-brane bounce, remain viable research directions.
Exploring Bouncing Cosmologies with Cosmological Surveys
hep-th 2014-05 conditional novelty 3.0 of 10

Two bouncing-universe models, the matter-ekpyrotic bounce and matter-bounce inflation, can fit the combined Planck and BICEP2 data at least as well as standard inflationary cosmology, with bounce scales below the GUT scale.
The Matter Bounce Alternative to Inflationary Cosmology
astro-ph.CO 2012-06 accept novelty 3.0 of 10

A contracting, matter-dominated universe that bounces reproduces the near-scale-invariant primordial spectrum usually attributed to inflation, and this review lays out how and with what observable consequences.
Introduction to Early Universe Cosmology
astro-ph.CO 2011-03 accept novelty 3.0 of 10

Cosmological perturbation theory applied to inflation, a matter bounce, and string gas cosmology shows all three can produce a scale-invariant spectrum, with distinguishable predictions in tensor tilt and non-Gaussianity.

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How the literature uses it

122 arXiv papers cite this in 156 sentences

Each citing sentence is taken from the citing paper's LaTeX source and typed by Pith's classifier. A label appears at probability 0.8 or more (0.95 for support), a contest at 0.7 or more; the quoted words are the citing authors'. How each label was checked · JSON

Papers citing it · 129 sentences without a confident label

Compares with it 3 papers

However from the analysis in [ref] the associated bounds are less strict than the ones that we found here so we will not refer to them in the present work.] ($ϕ_1, ϕ_2$ and $χ$) 1/M_Pl^2 (h^ T^ϕ_2_ )(h^ T^ϕ_1_ ) ⇒ 0 →ϕ_2 + ϕ^*_2 + ϕ_1 + ϕ^*_1 1/M_Pl^2 (h^ T^χ_ )(h^ T^ϕ_1_ ) ⇒ 0 →χ+ χ^* + ϕ_1 + ϕ^*_1 1/M_Pl^2 (h^ T^ϕ_2_ )(h^ T^χ_ ) ⇒ 0 →ϕ_2 + ϕ^*_2 + χ+ χ^* where we have neglected processes arising from the term $η_ h^ ł_χ|χ|^2 |ϕ_1 - ϕ_2|^2 /M_Pl$ since it is $O(10^-5)$ times smaller than the rest due to our $ł_χ$ choice.

UV-complete and stable Quintom Dark Energy models in the light of DESI DR2 · Planck-suppressed gravity-phantom interactions · 0.99
which is somewhat weaker than the rough estimate originally derived in Ref. [ref] .

Phantom fluid cosmology: Impact of a phantom hidden sector on cosmological observables · Constraint on $Λ$ · 0.99
In particular, when $γ_tot≪m^2$, our result reduces to that in [ref] .

Causality, unitarity and stability in quantum gravity: a non-perturbative perspective · Fourier modes of the propagator: conditions for microscopic violations of causality and relation with (in)stability · 0.98

Cites it as support 7 papers

* Causality violation and vacuum instability in the case $γ_tot<0$: While the propagation does not display any tachyonic instability and the microscopic violation of causality might still be compatible with observations, the fact that the forward-propagating degrees of freedom with $γ_tot<0$ carry negative energy, implies that the vacuum is unstable [ref] : the decay of the vacuum in modes carrying opposite energies (and opposite signs of $γ_tot$) is entropically favored, unless a microscopic breaking of locality or Lorentz invariance takes place [ref] .

Causality, unitarity and stability in quantum gravity: a non-perturbative perspective · Fourier modes of the propagator: conditions for microscopic violations of causality and relation with (in)stability · 1.00
In addition, there is also a quadratic divergence in the integral over velocity [ref] .

The New Ekpyrotic Ghost · Ghosts, singularity and vacuum instability · 0.97
Such a choice is, anyway, the natural and consistent one [ref] .

UV-complete and stable Quintom Dark Energy models in the light of DESI DR2 · Planck-suppressed gravity-phantom interactions · 0.97

Cites it as background 15 papers

Whether NEC violation can ever be stable (free of ghosts and gradient instabilities) has been the subject of much discussion [ref] .

Unitary null energy condition violation in $P(X)$ cosmologies · Introduction · 0.94
One class of scalar field models that accommodates $w < -1$ is the phantom field [ref] , which carries a wrong-sign kinetic term; the standard quantum objection is that such a ghost triggers catastrophic vacuum decay at a rate that diverges in perturbation theory [ref] .

Ghost Degrees of Freedom Without Quantum Runaway: Exact Moment Bounds from an Operator Conservation Law · Introduction · 0.81
One can refer to Refs. [ref] for more details on the pathologies induced by ghosts or tachyons, i.e. vacuum instability and causality violation.

Exorcizing Ghosts from the Vacuum Spectra in String-inspired Nonlocal Tachyon Condensation · Monster Zoology: Tachyons, Ghosts & Co. · 0.98

Discussion

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