Simultaneously bounded and dense orbits for countably many diagonal flows

Let d≥3d\geq 3, let Xd=SLd(R)/SLd(Z)X_d=\mathrm{SL}_d(\mathbb{R})/\mathrm{SL}_d(\mathbb{Z}), and let Im,JnI_m,J_n be index sets. Choose nonzero vectors {v1,i}i∈Im∪{v2,j}j∈Jn\{v^{1,i}\}_{i\in I_m}\cup\{v^{2,j}\}_{j\in J_n} in the diagonal subalgebra of sld(R)\mathfrak{sl}_d(\mathbb{R}) such that v1,i≠v2,jv^{1,i}\ne v^{2,j} for every (i,j)∈Im×Jn(i,j)\in I_m\times J_n. Define gt1,i=exp⁡(tv1,i)g_t^{1,i}=\exp(tv^{1,i}) and gt2,j=exp⁡(tv2,j)g_t^{2,j}=\exp(tv^{2,j}). Countable simultaneous-orbit conjecture. The set

⋂i∈ImB({gt1,i}t≥0)∩⋂j∈JnD({gt2,j}t≥0)\bigcap_{i\in I_m}B(\{g_t^{1,i}\}_{t\geq 0})\cap\bigcap_{j\in J_n}D(\{g_t^{2,j}\}_{t\geq 0})

has full Hausdorff dimension in XdX_d. The cases with only bounded or only dense conditions are known in stronger forms, while the simultaneous general case is proposed as an open conjecture.

References

Primary source

Dmitry Kleinbock and Chengyang Wu, “Simultaneously bounded and dense orbits for commuting Cartan actions”, arXiv:2509.05272 (2025).

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