In mathematics, the Dawson–Gärtner theorem is a result in large deviations theory. Heuristically speaking, the Dawson–Gärtner theorem allows one to transport a large deviation principle on a “smaller” topological space to a “larger” one.

Statement of the theorem

Let (Y_j)_j∈J be a projective system of Hausdorff topological spaces with maps p_ij : Y_j → Y_i. Let X be the projective limit (also known as the inverse limit) of the system (Y_j, p_ij)_i,j∈J, i.e.

${\displaystyle X=\varprojlim _{j\in J}Y_{j}=\left\{\left.y=(y_{j})_{j\in J}\in Y=\prod _{j\in J}Y_{j}\right|i<j\implies y_{i}=p_{ij}(y_{j})\right\}.}$

Let (μ_ε)_ε>0 be a family of probability measures on X. Assume that, for each j ∈ J, the push-forward measures (p_j∗μ_ε)_ε>0 on Y_j satisfy the large deviation principle with good rate function I_j : Y_j → R ∪ {+∞}. Then the family (μ_ε)_ε>0 satisfies the large deviation principle on X with good rate function I : X → R ∪ {+∞} given by

${\displaystyle I(x)=\sup _{j\in J}I_{j}(p_{j}(x)).}$

References

• Dembo, Amir; Zeitouni, Ofer (1998). Large deviations techniques and applications. Applications of Mathematics (New York) 38 (Second ed.). New York: Springer-Verlag. pp. xvi+396. ISBN  0-387-98406-2. MR  1619036. (See theorem 4.6.1)