Loop quantum cosmology vs string cosmology

[kodama]

which of the two is better supported by observational evidence and is more researched?

 

[Chalnoth]

Right now, they're both just paradigms for generating speculative models, and have no significant data backing them up. Which one a person thinks is better is largely down to personal preference.

 

[marcus]

There is a standard version of LQC used by major LQC researchers (e.g. Agullo, Ashtekar, co-authors...). It is consistent with the data, so far, on the early universe. And it also makes predictions which will be testable.
http://arxiv.org/abs/1509.05693
Detailed analysis of the predictions of loop quantum cosmology for the primordial power spectra
Ivan Agullo, Noah A. Morris
(Submitted on 18 Sep 2015)
We provide an exhaustive numerical exploration of the predictions of loop quantum cosmology (LQC) with a post-bounce phase of inflation for the primordial power spectrum of scalar and tensor perturbations. We extend previous analysis by characterizing the phenomenologically relevant parameter space and by constraining it using observations. Furthermore, we characterize the shape of LQC-corrections to observable quantities across this parameter space. Our analysis provides a framework to contrast more accurately the theory with forthcoming polarization data, and it also paves the road for the computation of other observables beyond the power spectra, such as non-Gaussianity.
24 pages, 5 figures

I think it adds to the confusion to lump "superstring cosmology" and LQC together and suggest that they are in the same boat--or essentially the same situation testing-wise. Actually Kodama's question is a reasonable one to ask and we ought to be able to distinguish, not blur the differences.

 

[kodama]

String Cosmology: A Review
Liam McAllister, Eva Silverstein
(Submitted on 16 Oct 2007 (v1), last revised 16 Jan 2008 (this version, v2))
We give an overview of the status of string cosmology. We explain the motivation for the subject, outline the main problems, and assess some of the proposed solutions. Our focus is on those aspects of cosmology that benefit from the structure of an ultraviolet-complete theory.
Comments: 55 pages. v2: references added
Subjects: High Energy Physics - Theory (hep-th); Astrophysics (astro-ph); High Energy Physics - Phenomenology (hep-ph)
Journal reference: Gen.Rel.Grav.40:565-605,2008
DOI: http://arxiv.org/ct?url=http%3A%2F%2Fdx.doi.org%2F10%252E1007%2Fs10714-007-0556-6&v=4882558e
Report number: SLAC-PUB-12782, SITP-07/17
Cite as: arXiv:0710.2951 [hep-th]
(or arXiv:0710.2951v2 [hep-th] for this version)
Submission history
From: Eva Silverstein [view email]
[v1] Tue, 16 Oct 2007 03:31:49 GMT (60kb)
[v2] Wed, 16 Jan 2008 02:48:12 GMT (61kb

 

[kodama]

marcus can you summarize 2-3 testable predictions?

 

[marcus]

Hi Kodama, thanks for asking,
I'll just have to go to the Agullo+Morris paper
http://arxiv.org/abs/1509.05693
Detailed analysis of the predictions of loop quantum cosmology for the primordial power spectra
and paraphrase or summarize some. Just saw your question and I'm on my way out but will see to it when I get back.

 

[kodama]

Hi Kodama, thanks for asking,
I'll just have to go to the Agullo+Morris paper
http://arxiv.org/abs/1509.05693
Detailed analysis of the predictions of loop quantum cosmology for the primordial power spectra
and paraphrase or summarize some. Just saw your question and I'm on my way out but will see to it when I get back.

sure. any chance u can also look at
String Cosmology: A Review
Liam McAllister, Eva Silverstein

and compare LQC with string cosmology

 

[marcus]

I think I'd prefer to continue focusing on the Agullo Morris paper (and the Ashtekar et al papers that led up to it by setting out and establishing this form of LQC).
Agullo and Morris are using notation and a set of equations governing the pre-inflationary era that were developed by Ashtekar and others in earlier papers which they cite. You might have a look yourself.

I see they use natural (planckian) units with c = G = hbar = 1 and they base everything on a parameter space (φ_B, m)
where m is the inflaton mass, and φ is a scalar field which evolves according to a given equation and assumes the value φ_B at the bounce.

Predictions for all the observable quantities (which might be used in testing) are then derived from particular choice of (φ_B, m).

So there are allowed regions of the parameter space which are consistent with what has been so far, and regions which have been excluded. You may be familiar with all this if you have already taken a look at the Agullo Morris paper.