Gamma in Brans-Dicke framework

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Discussion Overview

The discussion revolves around the behavior of the parameter ϒ in the Brans-Dicke framework, particularly in relation to the empirical relation of the scalar field Φ and its implications for gravitational constant G over time. Participants explore the transition from positive to negative pressure in the context of cosmic expansion and the influence of different epochs in the universe's evolution.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant presents an empirical relation for Φ and claims that the parameter n indicates G increases over time, leading to a specific behavior of ϒ that transitions from positive to negative pressure.
  • Another participant questions the source of the claims and requests clarification on the terms Φ and ϒ, indicating a lack of context for the discussion.
  • Further clarification is provided that Φ represents the scalar field in Brans-Dicke theory and ϒ relates to the pressure-density relation.
  • Several participants request citation of the study referenced, indicating a need for verification of the claims made.
  • A participant expresses skepticism regarding the credibility of the publication source, suggesting that the claims may be based on outdated or incorrect parameters, particularly concerning the ω parameter.

Areas of Agreement / Disagreement

There is no consensus on the validity of the claims made regarding the behavior of ϒ and the referenced study. Multiple participants express skepticism and request further clarification and citations, indicating a lack of agreement on the foundational aspects of the discussion.

Contextual Notes

Participants highlight the need for citations and express concerns about the credibility of the research source. There are unresolved questions regarding the definitions and implications of the parameters discussed, particularly in relation to the empirical findings presented.

Apashanka
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IMG_20190215_215221.jpg

I take an empirical relation of Φ=Φ0(a/a0)n where n=-(dG/dt)/GH ,present study shows n is negative ,implies that G increases with time
And using this fact and taking a scale factor of the form sinh(t) ,evaluated ϒ and then plot it with respect to t and got the above figure which is consistent with many other work done.
Present study shows ϒ(n,t0)=-0.67 to -1.67
n is chosen in such a way in the above plot.
From the plot it is concluded the transition time of positive pressure to negative pressure and start up time of the accelerated expansion.
But if we consider our universe to be dominated by radiation at very early epoch followed by matter then ϒ decreases from 1/3 to 0 and then -ve but this study and many other study shows ϒ increases first and then transit to -ve value as shown in the plot??
Is there is something which I am missing
 

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Where is all this coming from? What "study" are you talking about? What are ##\Phi## and ##\Upsilon##?
 
PeterDonis said:
Where is all this coming from? What "study" are you talking about? What are ##\Phi## and ##\Upsilon##?
Φ is the scaler field of Brans-Dicke theory and ϒ is of pressure relation P=ϒρ ,ρ is the energy -density
 
Please cite the study also
 
Dale said:
Please cite the study also
Page 4731
 

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Research India Publications is a known predatory publisher. I would be highly skeptical of anything found only in one of their journals.

Current evidence places the ##\omega## parameter at somewhere greater than 40000. The paper talks about ##\omega## on the order of unity, so I get the impression that the author may be unaware of the evidence. This could be a likely reason that the paper wound up in a predatory journal. I would not spend too much time on it.
 
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