Automatic continuity criterion for epimorphisms onto discrete groups

From papers

Let GG be a group such that every torsion subgroup of GG is finite, GG contains neither Q\mathbb{Q} nor the pp-adic integers Zp\mathbb{Z}_p as a subgroup for any prime pp. Let LL be a locally compact Hausdorff group and let LGL\twoheadrightarrow G be an epimorphism.

Automatic continuity conjecture. Every epimorphism from a locally compact Hausdorff group LL to GG is continuous if and only if GG has no non-trivial finite normal subgroups.

This conjecture would complete the known sufficient criterion for automatic continuity of epimorphisms onto discrete groups: under the stated torsion and subgroup hypotheses, the absence of non-trivial finite normal subgroups implies continuity. The converse follows from the existence of discontinuous epimorphisms onto groups with suitable finite normal subgroups, while the general equivalence is posed here as a conjecture.

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Primary source

Philip Möller and Olga Varghese, “On normal subgroups in automorphism groups”, arXiv:2208.05677 (2023).

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