Abstract
For a probability measure \( \mu \) on \( SL_d({\mathbb {R}}) \), we consider the Furstenberg stationary measure \( \nu \) on the space of flags. Under general non-degeneracy conditions, if \( \mu \) is discrete and if \( \sum _g \log \Vert g\Vert \, \mu (g) < + \infty \), then the measure \( \nu \) is exact-dimensional.
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Notes
We thank Yves Coudène for this observation.
cf. notations of the Introduction.
By convention, \( \log \left( \frac{{\mathbb {P}}_{(X,Y)}(A)}{({\mathbb {P}}_{X}\times {\mathbb {P}}_{Y})(A)}\right) {\mathbb {P}}_{(X,Y)}(A) =0 \) if \( {\mathbb {P}}_{X,Y} (A) = 0,\) the sum is \( +\infty \) if there is one \( A \in {\mathcal {A}}\) such that \( {\mathbb {P}}_{X,Y} (A) \not = 0\) and \( ({\mathbb {P}}_{X}\times {\mathbb {P}}_{Y})(A) =0\).
We will not discuss how, when restricted to \( T_Q\), our arguments would still hold under the hypothesis that the stationary measure is unique on \({\mathbb {R}}{\mathbb {P}}^{d-1}\) and that \( \chi _1 > \chi _2\). This would contain (and be very close to) [Rap21].
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Ledrappier, F., Lessa, P. Exact dimension of Furstenberg measures. Geom. Funct. Anal. 33, 245–298 (2023). https://doi.org/10.1007/s00039-023-00631-0
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DOI: https://doi.org/10.1007/s00039-023-00631-0