Is loop quantization in cosmology unique?

Understand

We re-examine the process of loop quantization for flat isotropic models in cosmology.

• In particular, we contrast different inequivalent `loop quantizations' of these simple models through their respective successes and limitations and assess whether they can lead to any viable physical description.
• We propose three simple requirements which any such admissible quantum model should satisfy: i) independence from any auxiliary structure, such as a fiducial interval/cell introduced to define the phase space when integrating over non-compact manifolds; ii) existence of a well defined classical limit and iii) provide a sensible "Planck scale" where quantum gravitational effects become manifest.
• We show that even when it may seem that one can have several possible loop quantizations, these physical requirements considerably narrow down the consistent choices.