I am an old (41-Years-old) physics graduate. I pretty much quit to "frequent physics" 10 years ago and my ability to manage physics is a bit rusty.
I was fascinated with Quantum gravity theory and especially with the model developed by Loll and Ambjørn and the related approach to quantum gravity that like loop quantum gravity is background independent.
https://arxiv.org/pdf/hep-th/0509010v3.pdf
https://arxiv.org/pdf/1105.5582.pdf
I was wondering what would be the minimum mathematical/Physical background required to study this theory given that as graduate I learnt the following arguments on modern physics

 - Nuclear physics

 - Quantum Mechanics

 - Special Relativity and Electrodynamics

 - Introduction to the Structure of Matter

I know this is a quite naive question but it is never too late to learn, it says.

Thanks