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## Main Question or Discussion Point

This new paper by Magueijo and Singh discusses prospects for observational Loop Quantum Cosmology

http://arxiv.org/abs/astro-ph/0703566

Joao Magueijo, Parampreet Singh

10 pages

from the abstract:

"Quantum gravitational effects in loop quantum cosmology lead to a resolution of the initial singularity and have the potential to solve the horizon problem and generate a quasi scale-invariant spectrum of density fluctuations. We consider loop modifications to the behavior of the inverse scale factor below a critical scale in closed models and assume a purely thermal origin for the fluctuations. We show that the no-go results for scale invariance in classical thermal models can be evaded even if we just consider modifications to the background (zeroth order) gravitational dynamics. Since a complete and systematic treatment of the perturbed Einstein equations in loop cosmology is still lacking, we simply parameterize their expected modifications. These change quantitatively, but not qualitatively, our conclusions. We thus urge the community to more fully work out this complex aspect of loop cosmology, since the full picture would not only fix the free parameters of the theory, but also provide a model for a non-inflationary, thermal origin for the structures of the Universe."

the next is from the conclusions section:

Loop quantum cosmology has the potential to relate observational physics and quantum gravity, allowing concrete calculations to be made in the quantum gravity regime as long as a minisuperspace approximation is assumed to be valid. The approach is known to modify the equation of state of ordinary matter, thereby permitting a solution of the horizon problem without resorting to scalar fields. It is then natural to ask whether in such scenarios thermal fluctuations could be behind the observed structure of the Universe. In order to analyze this issue we have assumed in this paper that physics learned in the mini-superspace approximation (in the sense of modifications to inverse volume terms) will not change qualitatively.

There are positive indications for this hope from ongoing work [28], but we stress this important caveat in our analysis.

We showed that prima facie we are confronted by a no-go result in classical physics...

http://arxiv.org/abs/astro-ph/0703566

**Thermal fluctuations in loop cosmology**Joao Magueijo, Parampreet Singh

10 pages

from the abstract:

"Quantum gravitational effects in loop quantum cosmology lead to a resolution of the initial singularity and have the potential to solve the horizon problem and generate a quasi scale-invariant spectrum of density fluctuations. We consider loop modifications to the behavior of the inverse scale factor below a critical scale in closed models and assume a purely thermal origin for the fluctuations. We show that the no-go results for scale invariance in classical thermal models can be evaded even if we just consider modifications to the background (zeroth order) gravitational dynamics. Since a complete and systematic treatment of the perturbed Einstein equations in loop cosmology is still lacking, we simply parameterize their expected modifications. These change quantitatively, but not qualitatively, our conclusions. We thus urge the community to more fully work out this complex aspect of loop cosmology, since the full picture would not only fix the free parameters of the theory, but also provide a model for a non-inflationary, thermal origin for the structures of the Universe."

the next is from the conclusions section:

Loop quantum cosmology has the potential to relate observational physics and quantum gravity, allowing concrete calculations to be made in the quantum gravity regime as long as a minisuperspace approximation is assumed to be valid. The approach is known to modify the equation of state of ordinary matter, thereby permitting a solution of the horizon problem without resorting to scalar fields. It is then natural to ask whether in such scenarios thermal fluctuations could be behind the observed structure of the Universe. In order to analyze this issue we have assumed in this paper that physics learned in the mini-superspace approximation (in the sense of modifications to inverse volume terms) will not change qualitatively.

There are positive indications for this hope from ongoing work [28], but we stress this important caveat in our analysis.

We showed that prima facie we are confronted by a no-go result in classical physics...

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