Parametric Khintchine-like behaviour conjecture for iterated function systems

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Let UU be an open subset of Rk\mathbb{R}^k, and for each u∈Uu\in U let Φu={ϕi,u(x)=Ai(u)x+ti(u)}i=1l\Phi_u=\{\phi_{i,u}(x)=A_i(u)x+t_i(u)\}_{i=1}^l be an iterated function system with attractor XuX_u. Let m\mathfrak m be a slowly decaying σ\sigma-invariant ergodic probability measure, with entropy h(m)\mathfrak h(\mathfrak m) and Lyapunov exponents λ1(m,u),…,λd(m,u)\lambda_1(\mathfrak m,u),\ldots,\lambda_d(\mathfrak m,u). Write H∗H^* for the class of functions used in the source and UΦu(z,m,h)U_{\Phi_u}(z,\mathfrak m,h) for the corresponding limsup set. Parametric Khintchine-like behaviour conjecture. If

h(m)>−(λ1(m,u)+⋯+λd(m,u))\mathfrak h(\mathfrak m)>-\bigl(\lambda_1(\mathfrak m,u)+\cdots+\lambda_d(\mathfrak m,u)\bigr)

for Lebesgue almost every u∈Uu\in U, then, under some weak assumptions on the maps AiA_i and tit_i, both stated conclusions hold: for almost every u∈Uu\in U, every z∈Xuz\in X_u and h∈H∗h\in H^* give UΦu(z,m,h)U_{\Phi_u}(z,\mathfrak m,h) full Lebesgue measure in XuX_u; and for almost every u∈Uu\in U and every z∈Xuz\in X_u, some h:N→[0,∞)h:\mathbb N\to[0,\infty) with ∑n=1∞h(n)=∞\sum_{n=1}^{\infty}h(n)=\infty gives a set UΦu(z,m,h)U_{\Phi_u}(z,\mathfrak m,h) of zero Lebesgue measure. This is proposed as a generalisation from the parameterised families accessible to the paper's methods; the required weak assumptions are not specified.

References

Primary source

Simon Baker, “Overlapping iterated function systems from the perspective of Metric Number Theory”, arXiv:1901.07875 (2020).

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