Variance and 2 point function in perturbation theory

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Discussion Overview

The discussion revolves around the relationship between statistical correlation in perturbation theory and the quantum 2-point function, particularly in the context of cosmological perturbations and vacuum fluctuations. Participants also explore the implications of the Bunch-Davies initial condition and its characterization as Gaussian.

Discussion Character

  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant questions whether the concepts of statistical correlation in perturbation theory and the quantum 2-point function are equivalent.
  • Another participant asserts that the discussion pertains to cosmology, specifically regarding cosmological perturbations during the early universe.
  • Some participants express agreement that the thread should be categorized under cosmology rather than quantum physics.
  • A participant suggests using the "Report" button to alert staff about the categorization issue.
  • One participant indicates they still require assistance with the topic.

Areas of Agreement / Disagreement

There is a lack of consensus on the appropriate categorization of the discussion, with some participants advocating for a return to the cosmology category while others have differing views.

Contextual Notes

Participants have not fully explored the implications of the Bunch-Davies initial condition or clarified the conditions under which vacuum fluctuations are considered Gaussian.

karlzr
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When we try to find the statistical correlation of some perturbation between two positions, we always calculate the quantum 2-point function. Are these two concepts really the same?
Also, people say vacuum fluctuation is gaussian. For normalized fields, we always use Bunch-Davies initial condition ##\frac{1}{\sqrt{2k}}e^{-i k \tau}##. So in which sense do we say it is gaussian?
Thanks! Any reference would be appreciated!
 
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It shouldn't have been moved to quantum physics. It is absolutely cosmology! Cosmological perturbations at very early times of the universe. I should have made it clear in the previous post.
 
Yes, I too agree that this should be moved back to cosmology.
 
I think you should try the "Report" button to get attention of somebody from the staff.
 
Still need help. Thanks!
 

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