Cosmological Evolution with Negative Energy Densities

Saharian, A. A.; Avagyan, R. M.; Mello, E. R. Bezerra de; Kotanjyan, V. Kh.; Petrosyan, T. A.; Babujyan, H. G.

doi:10.1007/s10511-022-09751-1

Cited by 5 publications

(2 citation statements)

References 27 publications

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“…Unlike dS spacetime, however, in AdS spacetime the negative cosmological constant corresponds to a negative energy density but with a positive pressure. Cosmological evolution with negative energy densities was previously studied in details in [73]. 6 This phantom crossing is achieved by exhibiting a pole/singularity in their equation of state parameter, which is quite different from the more well-known quintom models.…”

Section: Notesmentioning

confidence: 99%

An Effective Sign Switching Dark Energy: Lotka–Volterra Model of Two Interacting Fluids

Ong

2023

Universe

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One of the recent attempts to address the Hubble and S8 tensions is to consider that the Universe started out not as a de Sitter-like spacetime, but rather anti-de Sitter-like. That is, the Universe underwent an “AdS-to-dS” transition at some point. We study the possibility that there are two dark energy fluids, one of which gave rise to the anti-de Sitter-like early Universe. The interaction is modeled by the Lotka–Volterra equations commonly used in population biology. We consider “competition” models that are further classified as “unfair competition” and “fair competition”. The former involves a quintessence in competition with a phantom, and the second involves two phantom fluids. Surprisingly, even in the latter scenario it is possible for the overall dark energy to cross the phantom divide. The latter model also allows a constant w “AdS-to-dS” transition, thus evading the theorem that such a dark energy must possess a singular equation of state. We also consider a “conversion” model in which a phantom fluid still manages to achieve “AdS-to-dS” transition even if it is being converted into a negative energy density quintessence. In these models, the energy density of the late time effective dark energy is related to the coefficient of the quadratic self-interaction term of the fluids, which is analogous to the resource capacity in population biology.

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Section: Notesmentioning

confidence: 99%

An Effective Sign Switching Dark Energy: Lotka–Volterra Model of Two Interacting Fluids

Ong

2023

Universe

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“…where ρ + n is the familiar positive energy density and ρ − m is the negative cosmological energy density. The cosmic evolution with negative energy densities has also been studied in [11] where they mentioned vacuum polarization as an example for a gravitational source with ρ < 0 that may have played a significant role in early cosmic expansion.…”

Section: Introductionmentioning

confidence: 99%

Revisiting scalar field cosmology with $Λ(t)$ in $f(R,T)$ gravity

Ahmed¹

2023

Preprint

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Two scalar field cosmological models in f (R, T ) gravity with cosmic transit and varying cosmological constant have been investigated. The time-dependent cosmological constant Λ(t) is positive and tends to a very small value at the present epoch. The scalar field pressure p φ shows a sign flipping for normal scalar field. For the phantom field, the scalar potential V (φ) is negative and the energy density ρ φ = E k + V takes negative values when the equation of state parameter ω φ < −1. While the weak energy condition WEC implies that the total energy density ρ = i ρ i ≥ 0, we still can have a negative ρ term as long as the total ρ is positive. In the current work we argue that the WEC, ρ = i ρ i ≥ 0 and p i + ρ i ≥ 0, is not violated. For a scalar field φ, The conditionThe cosmology in both models has been probed using a given function a(t) deduced from the desired cosmic behavior which is the opposite of the conventional viewpoint.

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