Maxim Kontsevich and Don Zagier defined the algebra of periods and conjectured that one can pass from a representation of a given period to another one using only three rules. Assuming this conjecture, can we define the automorphism group of a given period using only these three rules? Can it lead to a method to prove that two periods are equal? Has such a question already been investigated?  

Thanks in advance and happy new year.



automorphism group of a given period
The idea that periods should be subject to a "transcendental Galois theory" has been first advanced by Grothendieck, who sketched a beautiful (but extremely conjectural) relationship with his theory of motives and motivic Galois groups. The resulting Period conjecture is very closely related to the Kontsevich-Zagier period conjecture that you mention in your question. I could give more details, but instead I will recommend this short and beautiful [survey](http://arxiv.org/abs/0805.2569) together with this other [survey](http://user.math.uzh.ch/ayoub/PDF-Files/periods-GKZ.pdf) for some recent developments.


