A Quintessence field equation of state

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The discussion centers on the equation of state parameter w for a quintessence field with a potential of m²Phi², questioning why it does not fall between 0 and 1/3 based on particle energy relative to field mass. It highlights that the scalar field is treated differently from usual matter and radiation because it is considered a classical scalar field rather than a collection of particles. This distinction arises from the understanding that scalar fields used in inflation are viewed as pure classical fields, challenging the notion that all modern physics must be quantum. Additionally, there is speculation that the treatment of the scalar field as classical may relate to its extremely low mass and large wavelength, similar to fuzzy dark matter, though this reasoning is not commonly applied to inflation fields. Overall, the conversation emphasizes the unique treatment of scalar fields in cosmological models.
fhenryco
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Quintessence field equation of state
Why the equation of state parameter w for a quintessence field with potential m²Phi² is not in between 0 and 1/3 depending on the energy of its particles relative to the mass of the field instead of the w resulting from formula 9 of https://arxiv.org/pdf/1504.04037.pdf which seems to be assuming that the field is classical ? !

In other words why is the scalar field treated differently than usual matter and radiation field when we want to compute it's w ?
 
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Because it is a classical scalar field, not a collection of particles.
 
It's also what i suspected but i wanted confirmation because i did not realize before that the scalar fields used for instance in inflation are understood as pure classical fields: i believed that in modern physics everything was always quantum and that nobody would accept a field which is not a quantum field !
 
fhenryco said:
It's also what i suspected but i wanted confirmation because i did not realize before that the scalar fields used for instance in inflation are understood as pure classical fields: i believed that in modern physics everything was always quantum and that nobody would accept a field which is not a quantum field !
Another possibility i was thinking about is that they treat it like a classical field because of it's extremely low mass (extremely large wavelength) ... this is what they do for fuzzy dark matter ... but i found nowhere the same argument for inflation fields
 
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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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