What does this paper say?

  • Thread starter wolram
  • Start date
wolram
Gold Member
4,235
553

Main Question or Discussion Point

We calculate the spectrum of density fluctuations in models of inflation based on a weakly self-coupled scalar matter field minimally coupled to gravity, and specifically investigate the dependence of the predictions on modifications of the physics on length scales smaller than the Planck length. These modifications are encoded in terms of modified dispersion relations. Whereas for some classes of dispersion relations the predictions are unchanged compared to the usual ones which are based on a linear dispersion relation, for other classes important differences are obtained, involving tilted spectra, spectra with exponential factors and with oscillations. We conclude that the predictions of inflationary cosmology in these models are not robust against changes in the super-Planck-scale physics.

Comment: 4 pages, 1 figure. One important correction in the Corley/Jacobson case with b_m>0 and some misprints corrected. To appear in Mod. Phys. Lett. A









http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0005432 [Broken]
 
Last edited by a moderator:

Answers and Replies

selfAdjoint
Staff Emeritus
Gold Member
Dearly Missed
6,764
5
Let's take it piece by piece:

We calculate the spectrum of density fluctuations in models of inflation
The density of matter in the universe will fluctuate depending on the physics; the fluctuations will come at various frequencies and the strengths of the fluctuations at each frequency form the spectrum. This can be estimated from the observations of the CMB.

based on a weakly self-coupled scalar matter field minimally coupled to gravity,
They introduce this simple field - it just has a magnitude, like a temperature, not any particle properties - as a surrogate for various microphysics theories (gravitons or quantum gravity theories).

and specifically investigate the dependence of the predictions on modifications of the physics on length scales smaller than the Planck length. These modifications are encoded in terms of modified dispersion relations.
Dispersion relations are the physicists' way to express things like scattering and refraction, typically of light, but also in this case the despersion of those density fluctuations, whose history we can estimate from the CMB data. By varying their field, they can represent different theories of gravity at the Planck scale, and calculate the resulting dispersion relations in each case.

Whereas for some classes of dispersion relations the predictions are unchanged compared to the usual ones which are based on a linear dispersion relation, for other classes important differences are obtained, involving tilted spectra, spectra with exponential factors and with oscillations. We conclude that the predictions of inflationary cosmology in these models are not robust against changes in the super-Planck-scale physics.
And they claim to find a strong effect; some microphysics changes the dispersion relations so that the history of the fluctuations doesn't match what we observe. While this COULD be due to their approximation (that scalar field), it is clearly a suspicious behavior caused by different kinds of microphysics. Thus a possible way to support some of them and falsify others.
 
Last edited:
wolram
Gold Member
4,235
553
Thank you SA,
nd they claim to find a strong effect; some microphysics changes the dispersion relations so that the history of the fluctuations doesn't match what we observe. While this COULD be due to their approximation (that scalar field), it is clearly a suspicious behavior caused by different kinds of microphysics. Thus a possible way to support some of them and falsify others.
 

Related Threads for: What does this paper say?

Replies
46
Views
16K
  • Poll
  • Last Post
Replies
12
Views
3K
Replies
2
Views
2K
  • Last Post
Replies
3
Views
3K
Replies
2
Views
2K
Replies
2
Views
1K
Replies
12
Views
4K
Replies
24
Views
17K
Top