LambdaCDM inflation model dependancies

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Discussion Overview

The discussion revolves around the various inflationary models that may underpin the \LambdaCDM cosmological model. Participants explore different inflationary scenarios, their classifications, and the relationship between these models and the initial conditions of the universe. The conversation includes theoretical considerations and references to prominent figures in cosmology.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express difficulty in identifying which inflationary models form the basis of \LambdaCDM, noting that multiple models may contribute.
  • Several inflationary models are listed, including tunneling models (e.g., double-field inflation, extended inflation, chain inflation) and rolling models (e.g., new inflation, chaotic inflation, hybrid inflation, natural inflation).
  • There is uncertainty regarding how to categorize slow roll inflation within the existing classifications of models.
  • One participant argues that there is no unique inflation scenario that is necessary for \LambdaCDM, suggesting that various scenarios could lead to the required initial conditions.
  • Another participant mentions Paul Steinhardt's shift away from supporting inflation as a necessary precursor for \LambdaCDM, proposing alternative scenarios instead.
  • Abhay Ashtekar's perspective is introduced, which includes a pre-inflation stage to explain slow-roll inflation, indicating a complex relationship between different stages of inflationary dynamics.
  • References to recent literature and papers are provided, suggesting that there are numerous inflationary models still consistent with observational data.

Areas of Agreement / Disagreement

Participants do not reach a consensus on which inflationary models are foundational to \LambdaCDM, with multiple competing views and ongoing debates about the necessity and role of inflation in cosmology.

Contextual Notes

Participants note the challenges in categorizing inflationary models and the potential for misleading information in existing literature. The discussion highlights the complexity of linking inflationary models to the \LambdaCDM framework.

Who May Find This Useful

This discussion may be of interest to those studying cosmology, particularly in understanding the interplay between inflationary models and the \LambdaCDM model, as well as the historical development of these theories.

Mordred
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I've been haqving a tough time tracking down which particular inflationary models form the basis of [itex]\Lambda[/itex]CDM.

the model I have discounted already is false vacuum A.Guth. some articles seem to suggest concepts from slow roll inflation. Others deal specifically with the inflaton field in the early universe inflation so I'm thinking eternal inflation is still used. I'm still looking for data on Roulette inflation just heard about it today lol.

Part of the problem with my search is that there is lots of misleading data on the search. Also the [itex]\Lambda[/itex]CDM model may derive from multiple inflationary models.

Any direction would be helpful, its more a curiosity on my part.

needless to say their is numerous inflationary models, I've been compiling a list of the variations
 
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So far my list of related include:

tunneling models:
(i) double-field inflation (Adams and Freese)
(ii) extended inflation (Steinhardt)
(iii) Chain inflation (Freese and Spolyar))

2) Rolling Models:
new inflation,
chaotic inflation,
hybrid inflation
Natural inflation (Freese,
Frieman, Olinto)

edit:: if my understanding of the group separation between otunneling models and rolling models, fundamentally it can be separated into degrees of freedom.

Still not clear on how to place slow roll. In terms of the above categories
 
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Mordred said:
I've been haqving a tough time tracking down which particular inflationary models form the basis of [itex]\Lambda[/itex]CDM.
...

The tough time does not seem so surprising to me because AFAIK there is no particular inflation that is basis for LCDM.

LCDM starts expansion with certain conditions, e.g. near flatness, near isotropy, a fluctuation spectrum appropriate for seeding structure.

People are free to imagine various scenarios calculated to produce these conditions. I don't think anyone has proven logically that ONLY SOME INFLATION scenario is capable of yielding these initial conditions.

I would say that so far there is NO one unique inflation scenario that "forms the basis" for LCDM.

People would do well to watch this talk by Paul Steinhardt, a world-class cosmologist who was one of the principle inventors of inflation. He seems to have now rejected it as a front-end prep for LCDM and is working on an alternative front-end scenario for LCDM.
http://pirsa.org/13030079/

Here's what Perimeter says about Steinhardt:
http://www.perimeterinstitute.ca/people/paul-steinhardt
"Currently the Albert Einstein Professor in Science, and on the Faculty of both the Department of Physics and the Department of Astrophysical Sciences at Princeton University, Dr. Steinhardt is one of the leading theorists responsible for inflationary theory. He constructed the first workable model of inflation and the theory of how inflation could produce seeds for galaxy formation. Among his awards is the 2002 Paul Dirac Medal of the International Centre for Theoretical Physics"

After being one of the principal inventors of inflation, he is now busy showing that LCDM does not require inflation.

Basically LCDM is a classic model of expansion cosmology once it got started.

People have speculations scenarios and opinions about how it got started (and these include various inflations and bounces) but they are not part of LCDM proper.
 
To balance the mention of Steinhardt with another major figure, consider Abhay Ashtekar.

The Springer press publishes a line of scientific Handbooks, and they are now bringing out a
Handbook of Spacetime, with Ashtekar as editor. From the looks of it this is going to be a massive project. Many top experts have been recruited to write chapters. the aim is to represent the state of the art in our understanding of spacetime geometry, gravity, cosmology.

Well, this his current take on a front end for the LCDM. He accepts a version of slow-roll inflation but then because THAT ITSELF NEEDS EXPLAINING he puts a pre-inflation stage in front of that to create the necessary conditions for a satisfactory inflation episode. And he is concerned with observational tests of this. Go figure :biggrin:

http://arxiv.org/abs/1302.0254
The pre-inflationary dynamics of loop quantum cosmology: Confronting quantum gravity with observations
Ivan Agullo, Abhay Ashtekar, William Nelson
(Submitted on 1 Feb 2013)
Using techniques from loop quantum gravity, the standard theory of cosmological perturbations was recently generalized to encompass the Planck era. We now apply this framework to explore pre-inflationary dynamics. The framework enables us to isolate and resolve the true trans-Planckian difficulties, with interesting lessons both for theory and observations. Specifically, for a large class of initial conditions at the bounce, we are led to a self consistent extension of the inflationary paradigm over the 11 orders of magnitude in density and curvature, from the big bounce to the onset of slow roll. In addition, for a narrow window of initial conditions, there are departures from the standard paradigm, with novel effects ---such as a modification of the consistency relation between the ratio of the tensor to scalar power spectrum and the tensor spectral index, as well as a new source for non-Gaussianities--- which could extend the reach of cosmological observations to the deep Planck regime of the early universe.
64 pages, 15 figures. Published version
 
There are hundreds of inflationary models, and you can read the latest Planck papers to see which are still consistent with the data. To start, this paper (http://arxiv.org/abs/1303.3787) compiles an encyclopaedia of solely single field inflation models, and splits them into different classes.
 
cristo said:
There are hundreds of inflationary models, and you can read the latest Planck papers to see which are still consistent with the data. To start, this paper (http://arxiv.org/abs/1303.3787) compiles an encyclopaedia of solely single field inflation models, and splits them into different classes.

Thanks for the link. The method you described is how I had generated the above list. I've been pouring over LCDM to inflationaty paradigm reviews. The above models are still considered good fits to observational data. Whether in part or overall.

Thanks for the above info on Steinhard Marcus. LQC I will eventually study if you happen to have a good step by step from the LQC original derivitaves to current development training articles. That will make my future LQC studies easier.

As you can see I enjoy studying the history of development. As if its done properly fills in the missing blanks in how this
formula or that derived.

Thus far the list above narrows down which of the multitude of inflation model alternatives to further study
 
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