Cosmological footprints of LQG (Aurelien Barrau and Julien Grain)

[marcus]

It's important to be able to test LQG with observations, most likely using new data on the microwave Background (CMB) collected by instruments such as the Planck spacecraft .

It turned out to be impossible to derive a prediction of dispersion (energy dependent speed of light) at least so far. So that particular avenue of testing does not seem to work. However there have been a number of papers recently which discuss how the spectrum of gravity waves imprinted in the CMB could be tilted in a calculable way by LQG.

These papers have been coming from researchers in several different countries, many of them exploring LQG phenomenology for the first time. The newcomer's names are often not familiar to me. I have made a more or less arbitrary choice of one of these papers, so as to have an example to consider, and, if we choose, discuss.

The lead author Aurelien Barrau (CERN) has an excellent publication track record and has earlier done research in string and stringy cosmology.

http://arXiv.org/abs/0902.0145
Cosmological footprints of loop quantum gravity
J. Grain, A. Barrau
Accepted by Physical Review Letters, 7 pages, 2 figures
(Submitted on 2 Feb 2009)
"The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated holonomy correction should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity."

The journal reference is Phys.Rev.Lett.102:081301,2009

 

[Evan Fox]

This is an interesting paper. It looks like observations of the CMB can indeed be used to test LQG and its modifications on the power spectrum of the cosmological tensor perturbations. It's really exciting to see research progress in this area, and I'm looking forward to seeing what further developments come from it.

 

[Entropia]

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The work by Barrau and Grain on the cosmological footprints of loop quantum gravity (LQG) is an important contribution to the field of quantum cosmology. As mentioned, it is crucial to test LQG with observations and the CMB is a promising avenue for such tests. While the initial approach of using dispersion to test LQG did not prove successful, the idea of using the spectrum of gravity waves imprinted in the CMB is a novel and exciting approach.

The fact that this work is coming from researchers in different countries, including newcomers to the LQG phenomenology field, speaks to the growing interest and potential impact of this research. The choice of one paper as an example is a good starting point for further discussion and consideration of the implications of LQG on the CMB spectrum.

Furthermore, the impressive publication track record of lead author Aurelien Barrau, who has also studied string and stringy cosmology, lends credibility to the findings and adds to the significance of this work. It is also encouraging to see that this paper has been accepted by a reputable journal, further validating its importance in the scientific community.

Overall, the work by Barrau and Grain provides a promising direction for testing LQG with observations and adds to the growing body of research on the cosmological implications of this theory. It will be interesting to see how this field develops and what further insights can be gained from studying the cosmological footprints of LQG.