Cosmological models with variable EoS

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The discussion centers on a new paper by Kumar and Xu that explores a cosmological model featuring variable equation of state (EoS) parameters for matter and dark energy. The concept of a variable EoS is not new, as highlighted by previous work from Ponce de Leon. The appeal lies in the model's continuity and its consistency with observational data from high redshift to the present. Participants are curious about the implications of this model, particularly regarding the EoS during the universe's early moments, specifically before 10^(-70) seconds. The conversation emphasizes the importance of observational constraints in validating cosmological theories.
Chronos
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An interesting and well presented new paper by Kumar and Xu:
"Observational constraints on a cosmological model with variable equation of state parameters for matter and dark energy" http://arxiv.org/abs/1207.5582
The idea of a variable equation of state for matter and dark energy is not revolutionary - e.g, "Cosmological model with variable equations of state for matter and dark energy" http://arxiv.org/abs/1204.0589 by Ponce de Leon. I find the continuity and consistency with observational evidence in modeling effects from high z to the modern era appealing.
 
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How was the EoS when the universe was younger than 10^(-70) seconds?
 
Abstract The Event Horizon Telescope (EHT) has significantly advanced our ability to study black holes, achieving unprecedented spatial resolution and revealing horizon-scale structures. Notably, these observations feature a distinctive dark shadow—primarily arising from faint jet emissions—surrounded by a bright photon ring. Anticipated upgrades of the EHT promise substantial improvements in dynamic range, enabling deeper exploration of low-background regions, particularly the inner shadow...
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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