A slight variant $\tilde Mot_{num}(k,\mathbb{Q})$ of the category of pure numerical motives $Mot_{num}(k,\mathbb{Q})$ is a Tannakian category equivalent to a category of representations of some algebraic group $GMot_k$:
In the sense of Galois theory, that algebraic group is called the motivic Galois group for pure motives. There is also a motivic Galois group of mixed motives.
That group is, or is closely related to, the group of algebraic periods, and as such is related to expressions appearing in deformation quantization and in renormalization in quantum field theory, whence it is also sometimes referred to as the cosmic Galois group. See there for more on this.
M. Levine, Mixed motives. (3.3 Motives by Tannakian formalism) In, Handbook of K-theory, Vol. 1, Friedlander and Grayson, eds., p. 429–521, Springer Verlag (2005).(pdf).
Joseph Ayoub, L’algèbre de Hopf et le groupe de Galois motiviques d’un corps de caractéristique nulle I, (pdf).
Joseph Ayoub, L’algèbre de Hopf et le groupe de Galois motiviques d’un corps de caractéristique nulle II, (pdf).
Joseph Ayoub, From motives to comodules over the motivic Hopf algebra, (pdf).
Joseph Ayoub, Lecture 1,Lecture 2,Lecture 3, The lectures were held within the framework of the (Junior) Hausdorff Trimester Program Topology and the Workshop: Interactions between operads and motives.
Ayoub’s weak Tannakian formalism applied to the Betti realization for Voevodsky motives yields a pro-algebraic group, a candidate for the motivic Galois group. In particular, each Voevodsky motive gives rise to a representation of this group. On the other hand Nori motives are just representations of Nori’s motivic Galois group. These groups are isomorphic.
the existence of a motivic t-structure (which renders the Betti realization t-exact) would imply the isomorphism of motivic Galois groups.
Matilde Marcolli, Gonçalo Tabuada Unconditional noncommutative motivic galois groups,(arXiv:1112.5422).
Matilde Marcolli, Gonçalo Tabuada Noncommutative numerical motives, Tannakian structures, and motivic Galois groups. J. Eur. Math. Soc. 18 (2016), 623-655. doi: 10.4171/JEMS/598
A quick survey is in
More is in
Jean-Pierre Serre, Propriétés conjecturales des groups de Galois motiviques et des représentations l-adiques, in U. Jannsen, S. Kleiman, J.-P. Serre (eds) Motives, Proceedings of Symposia in Pure Mathematics, AMS, vol. 55, part 1, 377 - 400 (1994).
Yves André, Groupes de Galois motiviques et périodes, (pdf), Séminaire Bourbaki, 68ème année, 2015-2016 n°1104.
AB Goncharov, Polylogarithms and Motivic galois groups, (pdf).
R Sujatha, Motives from a categorical point of view, (pdf).
Minhyong Kim, (Videos) Motivic fundamental groups and Diophantine geometry, I, II.
Annette Huber, Stefan Müller-Stach, On the relation between Nori motives and Kontsevich periods, arxiv/1105.0865
We show that the spectrum of Kontsevich’s algebra of formal periods is a torsor under the motivic Galois group for mixed motives over the rational numbers. This assertion is stated without proof by Kontsevich and originally due to Nori. In a series of appendices, we also provide the necessary details on Nori’s category of motives.
Mathoverflow, What are the possible motivic Galois groups over Q ?.
Mathoverflow, Why would the category of Motives be Tannakian?.
The Grothendieck-Teichmüller group is supposed to be a quotient of the motivic Galois group. This is a conjecture due to (Drinfeld 91).
A conjecture that the motivic Galois group naturally acts on the space of deformation quantizations of free field theories is in section 5 of
Regarding that this approach is related to Hodge theory periods, and that QFT can be attacked using the Batalin-Vilkovsky formalism, Barannikov has developed further the Batalin-Vilkovisky geometry and related Hodge theory in a direction which is probably a ground for better understanding of motivic Galois group as well.
An analogous statement, that a motivic Galois group naturally acts on structures in renormalization is in
For more along these lines see at cosmic Galois group.