Scale factors<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi><mml:mi /><mml:mn /><mml:mo>(</mml:mo><mml:mi>t</mml:mi><mml:mo>)</mml:mo><mml:mn /></mml:math>and critical values of the cosmological constant<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi></mml:math>in Friedmann universes

Scenarios of the cosmological evolution are studied by using an equation of state (EoS) having points where the specific enthalpy of the cosmological fluid vanishes. A large class of barotropic EoS's admits, depending upon initial conditions, analogues of the "Big Rip", as well as solutions describing exponential inflation followed by usual matter dominance; their classification is proposed. We discuss extensions to more general two-parametric EoS dealing with a pre-inflationary evolution and yielding stages with both increasing and decreasing energy density as a function of time. Possible cosmological scenarios with transitions from collapse to an expanding Universe or a closed oscillating one, without reaching a singularity are included.

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“…in Ref. [18]. Of interest is the connection of this phenomenon with the variable quark bag "constant" B considered in the present paper.…”

mentioning

confidence: 73%

Cosmological model with variable vacuum pressure

2014

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“…Recession velocities due to expansion have a different relation to the observed redshift [Eq. (19)] than do peculiar velocities [Eq. (18)].…”

Section: A Tethered Galaxy Has a Nonzero Redshiftmentioning

confidence: 99%

“…To obtain the z tot = 0 curve, we do the following: For a given v rec we use Eq. (19) to calculate z rec (for a particular cosmological model). Equation (17) then gives us a corresponding z pec and we can solve for v pec using Eq.…”

Section: A Tethered Galaxy Has a Nonzero Redshiftmentioning

confidence: 99%

Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects

Davis

Lineweaver

Webb

2003

American Journal of Physics

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We use the dynamics of a galaxy, set up initially at a constant proper distance from an observer, to derive and illustrate two counter-intuitive general relativistic results. Although the galaxy does gradually join the expansion of the universe (Hubble flow), it does not necessarily recede from us. In particular, in the currently favored cosmological model, which includes a cosmological constant, the galaxy recedes from the observer as it joins the Hubble flow, but in the previously favored cold dark matter model, the galaxy approaches, passes through the observer, and joins the Hubble flow on the opposite side of the sky. We show that this behavior is consistent with the general relativistic idea that space is expanding and is determined by the acceleration of the expansion of the universe -not a force or drag associated with the expansion itself. We also show that objects at a constant proper distance will have a nonzero redshift; receding galaxies can be blueshifted and approaching galaxies can be redshifted.

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“…Of the relativistic models (more precisely, Friedmann models), only those with a non-negative mass parameter (Ω M ≥ 0) and a non-negative curvature parameter (Ω K ≥ 0) and the corresponding critical dark-energy parameter (Ω Λ = Ω Λc = (4 Ω 3 K )/(27 Ω 2 M )) start expansion infinitely slowly from a value of R equal to (3 Ω M )/(2 Ω K ) (Bondi p.82). Felten and Isaacman (1986) have comprehensively reviewed all Friedmann models with non-negative mass density Ω M for all values of the cosmological constant Λ. The limiting (0,0,1) model is just the de-Sitter model.…”

Section: The 30/70 Modelmentioning

confidence: 99%

Can we observe galaxies that recede faster than light ? —A more clear-cut answer

Kiang

2003

Chinese Astronomy and Astrophysics

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Scale factorsR(t)and critical values of the cosmological constantΛin Friedmann universes

Cited by 82 publications

References 38 publications

Cosmological model with variable vacuum pressure

Cosmological model with variable vacuum pressure

Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects

Can we observe galaxies that recede faster than light ? —A more clear-cut answer

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